Inorganic Chemistry CHEM 3111
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Date Created: 11/02/15
Zeolitic Materials Ion Exchange and Shape Selective Catalysis Angus P Wilkinson School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta GA 303320400 Overview o Introduction 0 Zeolite structure 0 Zeolite synthesis 0 Zeolite application What is a zeolitic material o Zeolites are inorganic crystalline solids With small pores 120 A diameter running throughout the solid 0 They are aluminosilicate framework structures made from comer sharing SiO4 and A104 tetrahedra related structures can be made from AlPO4 and other compositions Building up zeolite structures sodalite or cage Secondary building units 41 651 52 5 1 1 4 41 5 3 Spiro 5 Fig 78 The various zeolite structures can be classi ed according to their secondary building units containing four or more tetrahedra the more common of which are illustrated here after Meier and Olsong The LTA framework Fig 72 for example can be constructed entirely by linking 4 4 units and see Table 71 Pentasil zeolites Fig 74 Projections along principal crystallographic directions of eight zeolite structures that contain 5ring units The structures drawn as straight lines connecting adjacent Tsites in each case are based on reported crystal structures The unit cell outlines are indicated by the dashed lines Pore connectivity ZSMS ZSMAll r 51 51 A Figure 510 A penlasil unit in colour together ml 3 slice of the stmcture of t X l 54 X 55 A LEM5 showing a linked chain of pentasll units highlighted m colour mquot 5 The immomecmg Chaml swam in ZSMS and ZSMJL Chiral zeolites o A chiral zeolite would allow enantioselective synthesis and separations Very dif cult to get optically pure chiral zeolite a bee b beb Fig 711 Representations of the two frameworks drawn as straight lines connecting adjacent T snesoxygen atoms are omitted and unit cell outlines are drawn of Wthh the structure of zeolite beta can be viewed as a disordered intergrowth 39 What is special about zeolites 0 They have pores with molecular dimensions leads to shape selectivity o There is a narrow range of pores sizes in the solid because the materials are crystalline crystalline gives better selectivity than non materials Pore sizes in zeolites Pen 5qu 3 Zeolite A ZSMS and Beta ZSMS Zeolite A 8 rings ZSMS 10 rings What types of applications are zeolites used for o Drying agents used for drying solvents 0 Shape selective separations eg devvaXing diesel fuel 0 Shape selective catalysis predominantly acid catalysis but also redox o Selective ion exchangers water softeners radioactive waste treatment Shape selectivity U U c T ransitinn state selectivity d Exterior cake formation Key structural features 9 You can make materials with a Wide range of pores sizes and shapes 9 Composition can be varied to tailor a materials properties pure SiO2 zeolites tend to be hydrophobic high alumina zeolites have a lot of charge balancing extraframework cations and have a very high af nity for polar molecules Extraframework cations o Extraframework cations are undercoordinated by the framework like to bind molecules in pore system to increase coordination number Sodalite unit Extraframework cations in Fauj asites Supercage Sodalite cage Undercoordinated cations 3A 4A 5A etc o What are 3A 4A 5A and 13X The number denotes the accessible pore size the letter denotes the framework changing cations tunes the pore size ALPOs O O O Q Microporous aluminophosphates can also be made Synthesis is usually at low pH with organic additives ALPOs have no framework charge SAPOs have a negative charge on the framework ALPOs limited to ring systems with alternating aluminum and phosphorous Titanosilicates o It is possible to make Zeolite frameworks that include tetrahedral titanium o A class of materials containing octahedral titanium has also been prepared 9 These titanosilicates are useful catalysts for selective partial oxidation reactions using peroxide oxidizing agents Zeolite synthesis 9 Zeolites and aluminophosphate microporous materials are made hydrotherrnally reactants are heated in water 100 250 39C For an aluminosilicate zeolite silica source Cabosil sodium silicate or SiOEt4 alumina source high surface area aluminum oxyhydroxide AlOEt3 sodium aluminate Al3 salts base pH 12 alkali metal hydroxide quaternary ammonium hydroxide etc template organic cation hydrated metal ion etc Templating agents o Pore size and shape can be controlled by growing the zeolite around templates r 19 I quot fquot 6quot f n W s zg l D a b TMA in ZK4 TPA in ZSMS Typical zeolite products Characterization 0 Most zeolite do not grow into large single crystals 9 Structural data can be obtained from 7 i powder diffraction techniques 7 ii electron microscopy 7 iii solid state NMR spectroscopy Zeolites and powder diffraction LAMBDA 12856 A I XIOE COUNTS O 0350 AND DIFF PROFILES I I quot o n I Iquot Iquot II I INVIOIII H I IIIcaInuluu 1 j J I l J A T J l l I i0 20 30 4 O ZTHETA DEG XIOE t quot39u lt IIn Ln 1 Flat 3 Highrrnlu don elmmn micaagain d39amlite hei vicwid dune u an Fug m 35 EC39 39le39 1 L llulu alin saruraure immu Imuiuim In an hr l39quotnnr 71h 1 i39rlnir nufg ructure u 1 lur wquot 0239 Ihirkmrs and dcr mui Thr umumnun Fumble mygr or my Phihrn ILEJT iFEI39 annmmion ele mn mmrmyg Du k39i39 29Si MAS NMR of zeolites A Al Al Al Si 0 O 0 0 0 Mosiom AIOSiOSI AlOSIOSiSEOSAOSI siosios o 0 g 0 O x Si 51 54Al SIGN 5ZAI S1Al 50Al 40 31 22 m on Si0Al 70 7100 t Figuge 514 Si MAS NMR spectrum al 796 MHz of the Rome analcnev Showing ve a sorpuons char clensuc of the ve possible pennumtions 0 Si and Al atoms anacth a the corners of the 50 tetrahedron as indicated Ion exchange With Na A o More sodium zeolite A is produced than any other zeolite o It is used as a water softener in powdered laundry detergents o In countries with low waste water treatment standards it is more environmentally friendly than polyphosphate Other ion exchange applications 0 Zeolites with good selectivities for Cs and Sr are available used to remove 137Cs and 90Sr from radioactive waste streams gtgt concentrate waste prior to disposal more robust than organic ion exchange resins gtgt not susceptible to radiation damage Separations 0 Gas separations such as 02N2 0 Straight chain hydrocarbons from branched chains using CaA straight chains are a problem for diesel fuel straight chains are useful for detergents 0 Water from organics extraframework cations coordinate to the water and remove it from the organic phase Silicon to aluminum ratio and hydrophobicity o Zeolites can be prepared with varying silicon to aluminum ratios 9 High silica zeolites are hydrophobic they are not wet they can select hydrocarbons from mixtures 0 Low silica zeolites are hydrophilic Hydrocarbon separations o Zeolite A can be used to separate straight chain hydrocarbons from a mix 0 Straight chains used to make detergents 5 nH lane 8 CaN a A Molecule in each case 0 1 2 3 4 5 6 7 8 9 10 Sodium ions replaced per unit cell O2 N2 separations 0 N2 is adsorbed more strongly than 02 in zeolites with a low SiAl ratio 0 This is a consequence of the quadrapole moment of N2 interacting with the extraframework cations 0 Used for gas separation but it has the disadvantage of being a batch process Catalysis o Zeolites are frequently used as acid catalysts ion exchange zeolite so that extraframework cations are protons ion exchange zeolite so that high charge extraframework cations bind water and release protons Lewis acidity at defect sites 0 Can do carbenium ion chemistry Catalysis with zeolites o The majority of the applications make use of the acidic properties of zeolites 6 Acid sites can be introduced by ion exchange for NH4 followed by thermal decomposition 0 Alternatively acid sites can be introduced by ion exchange for La3 followed by cation hydrolysis reactions 7 Ln3 H20 gt Ln0H2 H Dewaxing o Unbranched hydrocarbons have high melting points and tend to form waxes o Wax forming compounds in fuels are undesirable o Unbranched hydrocarbons can be selectively cracked in the presence of branched hydrocarbons using ZSM S Xylene isomerization o pXylene is needed for the production of polyesters o Xylenes can be rearranged over ZSMS can selectively obtain pXylene C5 AromCIIiCS 0 Isomerization is used as part of a cycle that separates pXylene from other compounds mm o4mz szm P4Iam mm OH EWAA P m mmN mmgo mmnpmam Retycre Xylene Transalkylation With xylenes o Transalkylation is an unwanted side reaction during xylene isomerization C C c c Acid catalyst Q 5 K c c c C r c in a Q l ca 1 a HTquot caa d c c as Transalkylation using toluene o Toluene can be converted to a much more valuable mixture of xylenes and benzene over ZSMS ooo Alcohol dehydrations 1AA luv 0 Alcohols can be lt icwH dehydrated to give alkenes lt 4 lt nC4OH selectivity depends on pore size 50 Conversion 39C CH n l I I 4 2 0 C 300 C Gasoline and zeolites 0 Most gasoline is processed using Fauj asite type zeolites high molecular weight materials are cracked second largest application of zeolites o Gasoline can be made by the dehydration of methanol over ZSM5 Mobile MTG process only used in New Zealand Molecular orbital theory OWe would like a theory of bonding that can be Visualized and is at least semiquantitative OWe have a picture of atoms with an electronic structure described by orbitals Why not do the same thing for molecules O Employ the orbital approximation l r1r2r3 wr1vr2wr3 How do we arrive at an approximation to the orbitals OThe electron density distribution for an electron in the Vicinity of a nucleus in a molecule should be similar to that found in the free atom OUse the idea of Linear Combination of Atomic Orbitals LCAO OWhat orbitals do we combine 0 Start with a minimal basis just the valence orbitals Page 1 Bonding in H2 9 Take two ls orbitals as the basis 9 Get two MO s V 1sA 1sB V 1sA 39 1sB m M What holds the molecule together 9 There is nothing magic about the molecule being bonded 7 Electrons preferentially spend time between the two nuclei They act as electrostatic glue 7 12 ltgt1SAl2 150902 1sA 1sB 1sB 1sA gtgt First two terms are electron density on original atoms other terms correspond to density between atoms Page 2 lnteratomic potentials 0 Molecular potential energy CHTVC 7 the equilibrium bond length corresponds to the minimum energy bond length 7 D8 is the depth of the potential well Vthe UVPES OHow do we know if the energy level diagrams have any meaning 9 We can compare to experiments that directly measure the orbital energies o Illuminate a sample with high energy radiation usually 212 eV in the UV and measure the kinetic energies of the ejected electrons Page 3 The PES expen39ment Kman mm 7 sinusme annnem n nu womanquot Photow uclmn mensz 1 W tum photon hi m m phawckclmn upomnt m trimming phumn ha my rm my in ms minim Alum 7 mm at nnmnn quotmy I on mm mm a km w Nagy MI I mulmmdrr drum mr mtme m phlvmdcdmnswlh durum mm min The PES spectrum of N2 Vibrn onal evais N r ISEeV N2 u r 167W Uri The W Dhulnctmirnn Spuuum of 313 The alternahvr ordering a nvbixai N quot 5quotquot mm 39 V nager found In harmnuclear dl tamlt amt mm the cxcrnnon at vmratmus m mm mm l N hccaxmn tamed by phmocjetltun 39 I2 0 1 Note nitrogen atoms have a first ionization energy of 145 eV Page 4 Construction of MO diagrams for other diatomics 9 We need to select a basis set 7 usually use valence orbitals 9 We need to categorize the basis orbitals according to their symmetry 7 only orbitals with the same symmetry have nonzero overlap 9 Figure out the relative energies of the orbitals 7 this may require help from spectroscopic data Classifying orbitals by symmetry O Orbitals in diatornics can be classi ed according to their rotatio s e characteristics as G 7 or These classi cations are strictly only valid for diatornics but we also 0 describe bonds between pairs of atoms in polyatomic molecules G orbitals 7t orbitals 5 orbltals Found in quadruply bonded I I 127 Page 5 MOs in first row diatomics 314 The molecular Glbi tal energy level iod 2 3l8 The alternative ordering of urbnal lnevgirs found in hamonuclear diatomic diagram should he used for 02 and F7 Dr C I f L N m cues mm I2 0 2 molecules Ungerade 0r gerade O MOS in molecules that are centrosymmetric can be classi ed as g or u 7 Useful for predicting spectroscopic transitions etc 7 g implies that the wavefunction does not change sign on inversion through the center of the molecule 11 means that it does change sign w u 21 rug and nu orbitals 20 g and rs orbitals Page 6 Experimental MO energies 1quot In mam m mum Enrvglu rm Palm 2 Momnnudmr mammm molecule as m E r Determining electron con gurations O The lling rules are essentially the same as those for atoms 7 Two electrons per orbital 7 Fill from the lowest energy up 7 If orbitals are degenerate go for the electron configuration with the highest spin Hund s rule 9 Consider O2 7 2 2 2 4 2 log 2039 36g 171 271g Page 7 Hetronuclear diatomics O The contributions to the MO from each of the atoms is unequal 7 w cA A cB B O The more electronegative atom contributes strongly to the bonding orbital O The less electronegative atom contributes strongly to the antibonding orbital 7 gives rise to polarity Orbital mixing Q The difference in energy between orbitals on different atoms leads to reduced mixing 7 The reduced mixing does not imply weaker bonding W C A AC s m via 5 WCA ALWa cA gt a 310 When two atomic orbitals with same energy in the atom Page 8 Hydrogen uonde Mamty F 321 The molecular orbital k magma lur HF The retat we rgy tvel usman af h axomic orbllals mum the inmzzhctn energies of the amms Carbon monoxide 322 The ma ncutzr mmtal enemy ch diagrim of co Note that the HOMO and LUMO are largely on c Important for metal 39 u m mm Wm H m nutmm by m at m WW Page 9 1C1 an interhalogen compound 324 A sthemaxm mmemlar uvhvml energy um Mugmm m m mluhzlogcn mnlncuk m as ca rumrd by an ab mmu pmcedulz Bond order 9 BO 12 X No bonding e No antibonding e 2 Band may w 2 Band order 15 m autumn of mm svmglh 125 In madman a hand mm and mu mm mm mm emu m key m m pn39mu 5 m samlt as mm Hg 3 25 Page 10 Bond strength bond length man 21 m mvvllztmn at band myth and mm mm m in rm 0 nmnls 5 m Sam 15 in Fly 3 25 H3 9 This species is postulated as an intermediate in some reactions ilt is the simplest triatomic molecule Page 11 Linear H3 16 1215A 212lt1215B 1SC 25 15A 39 1sc 39 2 3G 1SA 212431503 1SC In 12 Hu mu mmmm mum s 0 a uuposuu slum m We wavLumlmm Triangular ar 15A 431503 lsc yr 15A lsc 15A2 15B 15c 2 n M m m um mm mm Wm y hum W4 mm m Page 12 Correlation diagram Walsh diagrams 9 There is a relationship between the orbitals in the linear and triangular species This relationship how the orbital energies evolve on bending from linear to triangular is shown on a Walsh or correlation diagram I y 211 5 mm 31 uma a ea 330 The orb39ltal Curvtlzllun dlagram for an H3 molecu e s ows how rhe energies of Ihe orbltals change as rhe linear molecule becoma equllaleral tllangulav Three center two electron bonds O The orbitals in H3 are delocalized over the entire molecule 9 In H 2 electrons hold the molecule together 7 this is an example of a three center two electron bond Page 13 MO s for Polyatomic chains cm Constructing MOS for polyatomic chains Page 14 MOS for rings E E a m 388 Orbitals in more complex molecules O In general we form MOS from linear combinations of AOs with the correct symmetry properties 9 The energy of the MOs increases as the number of nodes increases 9 MOs made up from low energy AOs also have low energies Page 15 MOS for NH3 OThe basis set consists of 3 Hls orbitals and the N 2s and 2p orbitals O The molecule is known to have three fold symmetry O The N 2s and 2pZ orbitals have cylindrical symmetry also have three fold symmetry OThe linear combination H lsA lsB lsC has three fold symmetry a1 MOS for NH3 9 Combine orbitalsLCAOS with cylindrical symmetry to form MOS Page 16 e MOS for NH3 Q A combination of N 2pX and 2py orbitals and linear combinations of Hls orbitals have 6 symmetry T 2 Composition of NH3 MOS 2 g u I 8 2 Ali g v a Q 9 Page 17 MO diagram PBS for NH3 15 Ionization energy5V 331 The UV photoe cctron spectrum of NH using helium 21 cV radiation 313 m mm mm mm km mm a w m the mm M a cum mm W mm and mm mm SF6 and hypervalence A schema c mo ccular uvbnal enzrgy level diagvam for SFSV Page 18 d and f block organometallic compounds Shriver and Atkins Chapter 16 Why study transition metal organometallics OThere are an enormous number of known organometallics many of which show unusual structural and bonding motifs We have an opportunity to expand out chemical horizons OThey can be very useful catalysts synthetic reagents precursors The 18 electron rule and stability OMany stable organometallic compounds obey the 18 electron rule That is they have 18 valence electrons on the metal 18 electrons corresponds to an inert gas configuration for the metal gtgt althernatively you can view this number as being associated with complete lling of the bonding orbitals but none of the antibonding orbitals 18 electron rule can be used to predict stability Electron counting 0T0 count the valence electrons break the molecule into fragments so that each fragment is neutral sum up the number of metal valence electrons the number of electrons from the ligands and the charge on the complex MnCO539 gtgt Mn contributes 7e SCOs contribute 106 and the charge 1e The total electron count is 18 e Examples 9 Do the following species obey the 18 electron rule 7 Fec06 R CH3CO5 7 FeCO4239 Hapticity 9 To use the 18 electron rule we have to know how many electrons a ligand contributes to the bonding O This is not always a xed number as many ligands can bind in more than one way to a metal center 9 The number of atoms in the ligand which are directly coordinated to the metal is referred to as the hapticity of the O Hapticity is denoted n 9 Q Cquot c 00 l 50 5 b a S Mnm eHancou 7 mntcsugyzwicsusyz BwnylcsHsuqicsHsncml Types of ligand w l v Examples of electron counting M m bun 7 ml M 1 Wm a u u m u m Hr a m y A m Exceptions to the 18 electron rule 9 It is quite common for compounds of the late transition metals to form stable l6 electron compounds These are usually square planar d8 species 9 It is also common to nd early transition metal compounds that have fewer than 18e 7 Metal is too small and electron deficient to accommodate enough ligands so that it can achieve 18 electrons Scope of the 18 electron rule Usually less than 18e Usually 18 e 16 or 18 e Sc Ti V Cr Mn Fe Co Ni Y Zr Nb Mo Tc Ru Rh Pd La Hf Ta W Re Os Ir Pt Oxidation numbers 0 Oxidation numbers are not very important for organometallics except when considering oxidative addition and reductive elimination 0 To determine metal oxidation states we treat ligands such as CO as neutral but alkyl groups and hydrogen are treat as though they are anionic even though this sometimes seems contrary to their chemical behavior 0 Many organometallics have very low oxidation numbers Calculation of oxidation numbers 0 Just like any other compound OBreak the molecule ion up into fragments that are charged use electronegatiVity to guide you in doing this OIrCOClPPh32 IrI compound OWMe6 WVI compound OFePF35 Fe0 compound Oxidation number examples OWhat oxidation state is the metal in VCO639 MnPPh3CO4COMe HMnCO5 Carbon monoxide as a ligand 0 Carbon monoxide is one of the most important ligands in organometallic chemistry 7 A03 as a sigma donor and a 1 acceptor capable of stabilizing low oxidation states ML i c c i 7 6 donation Synthesis of carbonyl complexes 9 Direct reaction of the metal ot practical for all metals due to need for harsh conditions high P and T 7 Ni 4co 9 Nico4 7 Fe sco 9 Feco5 O Reductive carbonylation 7 Useful When Very aggressive conditions would be required for direct reaction of metal and CO gtgt Wide Variety of reducing agents can be used 7 Crci3 Al 6C0 A1C13gt Aici3 Crco6 7 3Ruacac3 H2 12CO gt R113CO12 HIngnssure gas supply Thamncmple Mela thermocouple well Glass container Stainless steel pleswre vessel IR spectroscopy and carbonyls O Vibration spectroscopy can tell you a lot about the structure and bonding in carbonyl complexes 7 CO vibrational frequency tells you about the electron density on the metal and how good other ligands are at removing electron density from the metal gtgt CO stretch frequency drops as the metal becomes more electron ric 7 CO stretch frequency tells you if the carbonyl is bridging or terminal 7 The number of CO stretching bands tells you What symmetry geometry the complex has gtgt This is an application of group theory CO stretch frequency 1 Q As the CO bridges more metal centers its stretching frequency drops 7 More back donation emu 2am 19m mm mm mom rm CO stretch frequency 2 Q As the metal center becomes increasingly electron rich the stretching frequency drops CO stretch frequency 3 Q The CO vibrational frequency can be used to measure the 71 acceptor ability of other ligands 7 Make complexes containing CO and another 7 acceptor ligand gtgt These ligands will compete for the metals 7 electrons As the 7 acceptor ability ofthe other ligand increases the CO stretch frequency will increase 9 7t acceptor series 7 CN39 NN lt CNR lt CO lt CS lt NO MISS Slmngar M 51mg Wankel Symmetry from Vibrational spectroscopy 0 IR and Raman spectroscopy can be used to deduce the ii a naslliliission shape of carbonyl complexes 7 Using group theory you can calculate how many IR can Raman active CO stretch bands you should have for a glven Shape IR spectrum ofliquid FeCO5 shows only two stretching bands Raman shows three bands This is consistent with group theory predictions for a trigonal bipyrarnidal shape Symmetry from Vibrational spectroscopy 2 L p L K x l U l u L x t x v M t x V u l 7 r x Example 9 IR spectrum shows bands in the bridging and terminal regions 9 Bridging IR band is single implying that the two COs 06 EC so are almost colinear 72mm 190m 300 i701 mm Cu 9 Two terminal IR stretch 53 bands implying that the two COs are not colinear Carbon 13 NMR of carbonyls O The 13C NMR of carbonyl complexes can tell you how many different environments are present if the molecule is not fluxional 7 Fluxional means that the COs or other groups exchange positions with one another rapidly 9 Many carbonyls are uxional 7 IR and Raman spectroscopy tell you about the structure at any one time gtgt They probe structure on a short time scale 7103912 see so you get a snap shot of What the structure is 7 NMR has a different much longer time scale and tells you about the time averaged structure Substitution reactions of carbonyls 0 Replacement of CO by another 2e donor say PPh3 can be carried out thermally or photochemically 7 This makes them versatile intermediates for the synthesis of other species 7 Can be enhanced by bubbling gas through the reaction to remove the CO 7 Photochemical approach can be very effective 0 The reaction usually occurs by dissociation of CO giving a solvated intermediate that then reacm with the nucleophile 7 In some cases the nucleophile participates in the rate limiting step Apparatus for photochemical reaction LWater cooled L lamp jacket K N2 C0 3 7 Ligand carbonyl solution 7 Mercury vapor UV Iamp Reactivity towards substitution 0 Reactivity varies from metal to metal NiCO4 readily looses CO CrCO6 needs to be driven gtgt high temps and N2 ush gtgt irradiation and N2 ush O The bulk of other ligands effects the rate of substitution big ligands enhance the rate of dissociative processes gtgt Because dissociation relieves the strain in the starting material Steric bulk and cone angles Cone angle 9 and dissociation Toman developed the constanth for Ni complexes idea of a cone angle to L e0 KdmolL39l quantify the bulk of a PCH33 118 lt109 ligand PCZH53 137 12 x105 9 Cone angles can be PCH3PhZ 136 50 XIO39Z correlated With rates of Pth3 145 large substitution and dissociation constants MB 182 large For NiL4 NiL3 L in benzene at 25 C See text for reference Electronic considerations 0 Most 18 electron carbonyls substitute Via a 16 e intermediate dissociative OHowever 16e complexes like IrCOClPPh32 go Via an 18 e species associative mechanism 0 Some 18 e compounds substitute Via an associative mechanism 7 they can avoid a 20e intermediate by ring slip one of the exiting ligands changes its bonding mode so that it is donating two fewer electrons or a similar mechanism The in uence of ligand type on substitution rate Q The presence of basic ligands coordinated to the metal center reduces the rate of CO substitution 7 Basic ligands in the metals coordination shell provide electrons that tend to strengthen M CO bonds 9 The basicity of phosphine ligands is 7 PF3 ltlt POAr3 lt POR3 lt PAr3 lt PR3 gtgt Note PF3 is a Very good 7 acceptor ligand even though it is not a Very good 0 donor 7 basic phosphjnes in the coordination shell Will M inhibit co substitution 1 a F The synthesis of carbonylate anions 0 Direct reduction of a carbonyl FeCO5 NaTHF9 FeCO4239 co 0 Reductive cleavage of a metalmetal bond 2Na Mn2CO10 9 2NaMnCO5 ODisproportionation by use of a good donor 3C02CO8 12W 9 2C0PY6C0CO42 8C0 gtgt Disproportionation is driven by the af nity of the metal cation for the added good donor ligand OReaction of bound CO with base 3FeCO5 40H 9 Fe3COH239 CO3239 2H20 3C0 Basicity of carbonylate anions Acidity Constant for demeial hydride in MeCN at 25 C 9 Many carbonylate anlons are Hydride pKMIH capable of acting as Bronsted HWCO 83 T T D Pb 113 bases HzFeCO ii 4 M1CO5aq Haq9 HCpCrcogt1 13 3 HllnCO5 HCpMoco3 13 9 9 Transition metal carbonyl W ltc gts 151 HoocoPigth3 15 4 hydrlde spec1es are o en best Hcpwcwi 161 regarded as H Mquot rather HCpMoCO3 171 than H Mt HzRuCO 187 HCpFEKCO2 194 O HCoCO4 has a s1m11ar ac1d Hcpmcwz m strength to HCl H205coo 208 7 note data in the text are for HReltCOgts 21 1 MeCN not water HCpFeltcogt2 263 HCpWCO2PMed 26 6 Nucleophilicity of carbonyl anions O Carbonylate anions are not only bases they can act as good nucleophiles making them useful reagents for the synthesis of a variety of organometallic species o MnCO539 Mel 9 MeMnCO5 1 CoCO439 MeCOI 9 CoCO4Ac 1 MnCO5 ReBrCO5 9 CO5MnReCO5 Br39 Reactions of bound CO OWhen CO is bound to a metal center that is not electron rich it is susceptible to nucleophilic attack at the carbon MeLi MoCO6 9 LiMoCOMeCO5 OWhen CO is bound to an electron rich metal the oxygen can become quite basic leading to reactions with lewis acids Migratory insertion 9 Mixed alkyl carbonyl systems can undergo migratory insertion reactions 7 A ligand bound to the metal center moves onto the carbon of a CO o lLnCO5Me PPh3e MnAcCO4PPh3 O O s ll H Lnn nico LHIYI 70 Me Lgt LrMM C Me Sol Me Sol Alkyls 9 Many transition metal alkyls are unstable 7 the metal carbon bond is weak compared to a metal hydrogen 0nd Q Alkyl groups with 3 hydrogen tend to undergo 3 elimination 7 M CHZCH3 9 M H CHZCHZ Fischer carbenes O CrCO6 PhLi OC5CrCOPhLi 7 Similar to enolate but the oxygen is nucleophilic O OC5CrCOPhLi Me3OBF4 OC5CrCOMePh 7 This is Fischer carbene It has a metal carbon double bond 9 Such species can be made for relatively electronegative metal centers 7 mid to late TMs 9 Fischer carbenes are susceptible to nucleophilic attack at the carbon Carbene reactivity Q Fischer carbenes act effectively as c donors and 7t acceptors Q The empty antibonding MC 7r orbital is primarily on the carbon making it susceptible to attack by nucleophiles 39 M c o 7 391 R R 7C Appropriate M um c a 6 for Fischer I a R OR I carebne quotquot A LUMOb1 V 29 M 0 IL 4 O R Appropriate R C for Schrock M lt b 5 iiiA carebne OR A R 6 W HOMOa 30 Schrock carbenes O The early TMs can be used to make carbenes that have nucleophilic carbons 7 CpZTilleCHZ Me3SiBr 9 CpZTiCHZSille3Me r Br39 Appropriate R C for Schrock 5 A carebne OR A Alkenes as ligands O Alkenes can bind to a metal center and act as both a 6 donor and 7t acceptor 0 One of the earliest such complexes was Zeise s salt 7 KsztCh HZCCHZ SnClZ9 KPtCl3nZCZH4 KCl 0 Species can also be prepared by abstracting a beta hydrogen from an alkyl ligand using the trityl Ph3C cation l R l R R 34 Alkene binds face onto the metal center DewarChatt model for bonding O Bonding in alkene complexes is often described in terms of o donation from the 71 bonding orbital of alkene to a quot the metal and 71 acceptor behavior involving the 71 M antibonding orbital on the alkene 7 This is the DewarChatt model The synthesis of TE allyl complexes o 2C3H5MgBr NiCI2 e Nin3C3H52 2MgBrCl H 0 c C 0 H CH CH 1 C A 2 2 H2C CHCHZCI 8 oc Mn CH2CHCH2 gt 06 Mn co 1 1 V V Mnco51quot 0C c cr 0C Co C o C0 Isome sm and 7 allyls Q lnterconversion of syn and anti is often observed 7 Probable mechanism involves n3 9 n1 9 n3 a ma admin nnnn ni mum i m x mm nnmi Ins s i awnWin Kmmmnl Alkyne complexes 9 Alkynes can also act as ligands 7 Sometime as 4 electron donors notjust as 2e donors r isu Wilmile min in n rimna in Slum I u suwm M L mm r I o n mam n iimwinin mi m Mini quotWm mu Reml uuu na minim I an m a l Ligand behaving w as a 2e donor quotC E C Ligand behaving DECK 1an sa4e donor I d a c a o 41 cannangpnncon Metallocenes O quot wld metal center 0 The most common ring ligand is Cp cyclopentzdienide but many other le rings are possib Q g e m o e F 1531 Some examples or kmwn melallncencs cnnlammg four vc m wvcn mm eighhmumburul rinsx The synthesis of Cp complexes ONan is a good source of nucleophilic Cp 9 2Nan MnCl2 9 Mnsz 2NaCl O This approach works for Fe Co and Ni Reactions of ferrocene Q Ferrocene Fesz is very stable and the rings can be modified by electrophilic substitution or by metallation to produce a nucleophile that can then be reacted with a wide range of electrophiles m Cchucl FequCEHalz 7 pa t l us Fehr39ecshsl 7 Fe cm 0 Ll Bent sandwich compounds and triple deckers Q It is possible to construct stacks of metallocenes to form triple decker complexes 9 The earlyTMs often incorporate other ligands along with the two 7 IN I39CM ngs to form bent sandwich WWW compounds I m 7 Other ligands help raise the electron n9 Ynltcl countcloser to 18 e c k 939 Mm malva 7 Can View these species as sandwhiches with 3 forbitals projecting out of the sandwich that are available for chemistry Bonding in ferrocene Q Ferrocene s most stable conformation is eclipsed V 39 rather than staggered f e conesponols to lling a11 ofthe bonding and V nonbonding orbitals gtgt a is effectively nonrbondlng duetova39ypoor overlap of ill with the ring orbitals new 99quot Correlation of electron configuration and properties Electron con gurations and MVC bond lenghs in O The reactivity and MC 9 mm um bond 1amp1ng In Msz Compound Va e Electron RMC compounds Q be electrons con g U correlated With the orbital Y2 q occupation if e is View as VC5Hs2 15 94 al 228 antibonding a is non 3 bonding and ez is bonding MCSHS 16 e a 23917 e an sometl es think MmCSHACH zi 17 91133 ml about e and aquot as being analogo o the t7 Fe C H 18 via o orbitalsin an octahgedral 5 5 e complex and the e being C C H 19 via vie quoti like the eg orbitals 5 5 e gtgt Have high an low spin lb 12 7 possibilities N C5H52 2 9 a 9 Cp complex is high spin Metal Vapor Synthesis MVS 9 Individual metal atoms are very reactive They can be used to prepare things that would otherwise be very difficult to make 7 Can produce metal atoms by evaporating pieces of metal 9 MS 9 Mg 9 MT6C6H62 at Is 41 Am lepzlnlu39 ubmuuh um mvnnl him i mm mmer mpmm w Mmmmaemmhm mmkuun mm m mszkle u I mman MIAyxu u I 1 W m J u I Immmmmml Fluxional polyenes 0 Rings in metallocenes as Fe quite mobile There are very low barriers between different conformers 0 Many polyenes undergo I s 4 I I I rapid hoping Via 12shifts Shem3 l CH 5 FluXionality and NMR 9 The mobility of the ringspolyenes can be studied N R in many cases At hig T you get spectra that re ect a time average structure and at low T you get spectra that represent the instantaneous structure 7 From the changes with temperatureyou can leam about the mechanism associated with the mobility and the activation barrier to mobility s i 9 e lt I 2 A H spectra are for RumAcgngxcoh At high u see an average signal Atlow Tyou see the 4 distinct types ofproton su Reactivity of early TM organometallics 9 Early TM organometallics are oxophilic 7 tend to form compounds with O or some other hard donor bound to the metal 9 Early TM organometallics tend to undergo CH bond cleavage reactions 7 CH bond activation is a potentially useful property Methane is a very abundant feedstock Reactions of early TM organometallics Cp Cp C Cp H H2 0CH3 Zr CO gt Zr H gt Zr H H Cp Cp H Cp Cluster compounds 0 Metal cluster compounds are widespread in organometallic chemistry OAny molecular species that has metalmetal bonds can be regarded as a metal cluster compound 9 For the dmetals metalmetal bonding is stronger for the heavier metals 4d and 5d more 4d and 5 d clusters than 3d clusters Examples of cluster compounds Electron counting rules O The stability and geometry of many cluster compounds can be predicted using Wade MingosLauher rules 9 These are closely related to the rules used for electron counting in boranes 9 Stable clusters have their bonding orbitals lled and vacant antibonding orbitals 7 Cluster Valence Electron count CVE should just fill these orbitals Examples of stable geometries For different VFs Syntheses of clusters O Pyrolysis of lower molecular weight species 7 2C02CO8 heat9 Co4CO12 4C0 7 not a clean route 9 Redox condensation F63CO112Jr FCCO5 9 F64CO132Ur 3CO 9 Base promoted CO loss Rh4CO12 8OOCiPI39OHHz9 Rh13co25H32 Rh15co27l339 Electronic spectra of TM complexes Chapter 13 Atkins and Shriver Electronic spectra 0 Transition metal complexes often av absorption bands in the V1 their interesting coloration 7 These bands come from a combination of dd excitation involving just the metal d orbitals and charge transfer transitions 0 e Studying spectra provides structure in these species 7 Transition metal spectroscopic industrial pigmentrs display devices lasers etc h 3915 w m Trr Ana lughr thal Lm H Maqmlled amornimn sun Mnm 2m 39 Ana laconnem39l lzsuuucm39l manom l m lursvulmmlll llvi il mmitlu mum b wlmlv llswimmutanttsunami a a The bandlabeled CTis a charge transfer transition all the other absorptions are dd MO diagram for an octahedral complex 9 Possible transitions include ones between 1 orbitals between ligand based orbital and d orbitals LMCT and between the metal d orbitals and ligand orbitals MLCT Complex Ligands Anti bonding Non bonding Bonding dd transitions O The spectra of complexes with more than one 1 electron usually contain more than one dd band This is because the electrons in an atom or ion feel each others presence and interact gtgt They repel each other 9 For example a d2 electron configuration ion gives rise to five different energy terms five energetically distinct ways of arranging these electrons even in the case of a free ionatom In the presence of a ligand eld even more distinct terms are possible leading to many possible transitions Coupling of angular momenta O For lightish elements the energetically distinct ways of arranging electrons in a free ion are characterized by different orbital L spin S and total angular momenta J The orbital angular momenta of the individual electrons l couple with one another to produce a state with well de ned total orbital angular momentum L For two electrons with angular momentum quantum numbers 11 and 12 o L 11121112 1 11 12 The spin angular momenta of the individual electrons s couple with one another to produce a state with well de ned total spin angular momentum S Spin orbit coupling O The orbital and spin angular momenta L and S couple together in a vector fashion to give a total angular momentum J Different values of J have different energies SI III 10 13 ForLl andSl wecan ForL2 andSl wecan achieve J values of 2 l and 0 achieve J values of 3 2 and l Free ion terms O For a free ion we can label all the energetically distinct ways of arranging electrons using Term Symbols 25 LJ where S is the total spin angular momentum for the term or state L is the total orbital angular momentum of the state and J is the total angular momentum for the state gtgt Note L is usually denoted by a letter where S P D F etc correspond to L 0 l 2 3 etc gtgt ZSl is called the multiplicity singlet doublet triplet etc 0 Several different terms can arise from a single electron configuration 9 Each term has a different energy Hund s rules O Hund proposed a set of rules to help decide which term is lowest in energy 0 The ground state term always has the highest possible multiplicity 0 If there are several terms with the same multiplicity then pick the one with the largest value of L Deriving free ion term symbols 0 If the electrons are in different type of atomic orbitals all possible combinations of l and n1S are possible and life is easy 0 If more than one electron occurs in a given type of orbital 2p2 3d2 3d3 4f21 etc then care must be taken as some terms will be forbidden by the Pauli principle Deriving term symbols 2 Q If the electrons are different orbitals all possible terms can be arrived at by considering all possible combinations of l and s for the available electrons 7 Consider sld1 gtgt SpinScanbe 2 2or 2i 2 o ie S 1 or 0 gtgt L can be 20 or 20 gtgt Possible terms are 3D and 1D neglecting different values of I Deriving term symbols 3 7 Consider pld1 gtgt SpinScanbe 2 2or 2i 2 o ie S 1 or 0 gtgt L can be 21 2 or 21 all possibilities between the two extremes derived by adding or subtracting the individual 1 s gtgt Possible terms are 3F 3D 3P 1F 1D and 1P 7 Consider pldlf1 gtgt SpinScanbe 2 2 2or 2 2 2 o ie S 32 or 2 gtgt L can be 32l 5 4 3 2 1 321 all possibilities between the two extremes derived by adding or subtracting the individual 1 s gtgt Possible terms are 4I 4H 4G 4F 4D 4P 4S and 2L 2H 2G 2F 2D 2P 2S Microstates 0 To work out the possible terms for a case where more than one electron is in a given set of orbitals we need to set up a table showing the allowed microstates 0A microstate is a specified set of values of m1 and n1S for each electron OWe then associate the possible microstates with terms Microstates for atomic carbon 9 Atomic carbon has a ls22s22p2 electron con guration We can set up a chart showing all of the possible ways of arranging the pair of p electrons showing all the microstates ML 2 0 2 H 0 39I l 0 l I 0 39l 1 0 H H H H H H t H ll 11 l quot H H H ll 11 M3 0 0 0 l 1 1 l quotl l 0 0 0 0 0 0 Microstates for atomic carbon 2 0 We can collect these possible microstates into a chart set up accordmg to total MS and ML for each microstate left below Mu 1 0 139 M 2 I x 1 0 1 l x xx X x x X ML 0 x xxx x ML 0 x x x From 3P x n x H x x x 2 x 2 We now have to figure out which terms these microstates correspond to We start to do this by considering the microstate with highest MS and highest ML with this MS in this case MS 1 and ML 1 This microstate must belong to a 3P term We now eliminate from the table all of the other microstates that would come from this term and work on what is left Microstates for atomic carbon 3 0 We now examine the microstates that are left after eliminating the first term and try and figure out the next term and so on The remaining microstates above left after eliminating those from the 3P term can be broken down into a set that must come from a 1D term middle and another set that must belong to a 1S term right Energies of different carbon terms 5 W I 216484 1 Note the large energy 39 differences that can I arise between terms just due to electron electron repulsion Differences due to E 1 In 5 1 10mm cmzmpz changes in J are small compared to those due i 435 to changes in S and L 3quot a 3 This is generally true T 396quot for light atoms i I 5 E0 SEHCE lquotltr1u h Spallllllllg In the groundstate IJILt ZpZ con guration of carbon All ener W mst lm Qil ir39Tii 39S toenlnszare split a a result of electron electron repulsion Th 39 r I as a resu t of spinorbit cou lin Th ILCl39BlS crammed In this gure From DeKock R L Gray HPB ghemjcfz lgfronh m ondmg BenjamInCummings Menlo Park CA 1980 Reproduced with pennis dl Microstates for a 12 con guration a E E n Term 0 We can go through a similar process of examining microstates for a d2 electron con guration i wmlt02 xx xx ww rnunun N m OMMOg w 9139 A ID1 hallmark un t M H 39l Y M l 11 011 1Ul 4 3 3 a m a Mcrostates 1n come from F term mrcrostates 1n come from a 2 m 39239 2390quot 3P term microstates in a box come from a 1G term and microstates in a l 2 m cum 2 I m0391 circle come from 1P term There is 1 0 ro one other microstate that comes from 18 term 2 2 1 1 2 2 2 2rr o o I 1 1 9390 The Racah repulsion parameters O The different free ion terms for an electron con guration have different energies due to variations in electronelectron repulsion O The different energies can be expressed using a small number of electrostatic parameters A B and C These parameters are integrals related to the extent of electronelectron repulsion The larger they are the greater the repulsion is 9A B and C are called Racah parameters Energies of d2 free ion terms OECS A 14B 7C OE1GA4B2C OE1DA3B2C O E3P A 7B O E3F A 8B 9 Note that the difference between any pair of these terms is purely a function of B and C not A Q If we can measure the energies of two properly chosen spectroscopic transitions between these terms we can calculate B and C Values for Racah parameters O The Racah parameters depend on ion size 7 The smaller the ion the larger B and C get Essentially as you con ne the electrons to a smaller Volume they repel each other more 9 The ratio CB is almost constant and close to 4 Table 12 Racah patzvncms lo sumr dmm lUnS39 Iv 2 1 4 H mm 71 v 7050 9 43 0 mm H mmum mama I gt Mu mum mmm r Co nzuu v N 122w U 124m xv 39ln mm rims me u nnrzmnrr wzvh m Va no u mu m parcmhvscs u is m cmquot Ligand field transitions 9 When a spherical ion is placed in a lower symmetry environment the degeneracy of some of the terms is broken 9 For an octahedral field 7 s gt A1g 7 P gt T1g 7 D gt Eg ng 7 F 77gt T1g ng A2g O Transitions from the ground state to all of these new states are possible 7 This leads to quite complicated spectra Predicting the loss of degeneracy OThe way in which the degeneracy of a state is broken by lowering the symmetry of a species can be predicted using group theory Going from a spherical ion point group R3 to an octahedral complex is just a symmetry lowering as far as group theory is concerned OThe results from these predictions are tabulated in tables for descent of symmetry Descent of symmetry tables 0 0 71 Th D42 Du A Al Al Ag A A A2 A2 A2 Ar Bl A20 5 E E E9 A19 Bio Ea T1quot T1 T1 tr A2 E A E T1 T2 T2 T 329 13 7 A1 E Aiu Al A2 Au A A A2quot A2 A1 Au Bra 31 E E Eu A1 Btu Eu Tlu T1 T1 Tu A21 Eu A214 E T2 T2 T1 Tn 3214 Eu Am Eu Other subgroups T D4 D24 C4quot C4 21 D3 C3 5395 Cu 54 3C2u20212C2h5 C352C21S2 Cr R3 0 D4 D3 5 A1 A1 A1 P Tl A1E A2E D ET2 A1BIBZE A2E F AzTITz A2B1Bz2E A2AZZE G A1ET1T2 2A1A2BlBz2E 2A1A23E H E2TT2 A12A2BBZSE A12A24E d1 correlation diagram for Oh O The energetic effects of the loss of degeneracy generated by symmetry lowering can be illustrated on a correlation or Orgel diagram Here the ground state 2D term of a d1 isolated ion is split into two different states by the octahedral field 2E29 A0 Energy 2 0 T29 Increasing ligand field strength gt 133 Correlation diagram for a free ion left and the strong eld terms right of a d1 con guration d2 correlation diagram for Oh O The free ion terms for a 12 metal 933A2 2A are also split by insertion into an 153 octahedral eld 3F into 3A2g 3T2g and 3T1g 3P into 3T1g no split 0 We can work out the electron Increasing gand ems enmh con gurations corresponding to 134 Common diagram for a free ion these states using group theory Selef a g39 e39d term right f Note that on the left hand side of the diagram weak eld limit A is extremely small relative to B and C the splitting is expressed purely in terms on B and C On the right hand side of the diagram strong eld limit A is very big compared to B and C the splittings can be expressed purely in terms of A In the middle the diagram the relative energies of the states depend on B C and A Energy Deriving the possible states from the strong eld limit OFor two parallel spin d electrons in an octahedral complex we can have three different electron con gurations t2g 1g t e gt 3T 3T 2g g 2g 1g 2 gt 3 eg AZg OPossible states are derived using group theory using direct products or determined by examination of a direct product table Direct product table 7 FothOt T0 7 O The possible states A A2 E T Tz that you can get by A1 A A2 E n T2 havrng electrons 1n A A a r r two different orbitals E 35 T2 T2 can be read off from a T1 hymn g 2 direct product table T AIE T1T2 To use this table select the orbital symmetry of one electron across the top and orbital symmetry of the second electron down the side At the intersection of the row and column you are given the allowed symmetries of the states involving the pair of electrons For example if you have two t2 electrons you can get a 3T1 state and 1A1 1E and 1T2 states If you have an e and a t2 electron you can 1T1 1T2 3T1 and 3T2 states Tanabe Sugano diagrams 9 Correlation diagrams are not quantitative They just show in a general sense what happens to the energies of terms as a function of A O TanabeSugano diagrams illustrate the relative energies of states in a quantitative fashion They are drawn for a xed ratio of BC 4 The ground state always lies on the xaxis They can be used along with spectra to estimate both A and B for a given complex Tanabe Sugano diagrams 39A1 1 3A1 O TanabeSugano diagrams include the effect of mixing states with the same 1 symmetry 3T Electronic states with the same symmetry 3T can not cross they always mix 1A This introduces the curvature seen for many of the lines on the plot State 2 gt U 39 a a 5 T 10 20 30 1 AoB 135 The TanabeSugano diagram for the Changiw parame e d2 con guration A complete collection of 136 The nonerossing rule states that if diagrams for dquot con gurations is given in two states of the same symmet ar Appendix 5 at the back of the book The likely to cross as a parameter is changed d f as shown by the thin Iin l they will in par39ty SUbscnpt g has beequot omme mm fact mix together and avoid the crossing the term symbols for clarity 85 Showquot by the my quotml Using a TS diagram 0 We can use a TS diagram by first trying to assign the observed spectrum decide which transitions are responsible for the bands V 112 00472M VlClo llHCIO I K 5 a Mr ld l roseM MMCIDAII L a lull 393 l 39 i First two bands in V3 spectrum probably involve transitions to the 3T2 and 3T1 states 3A2 also seems possible but does not work out in the later part of the analysis 1E and 1T2 are not likely as the nal states as transitions involving a spin state change are extremely weak as in the Mn2 spectrum Using a TS diagram 2 0 Having identified two bands take the ratio of their transition energies 25500 17000 1 5 and find the point along the AB axis on the TS diagram that corresponds to this ratio AB27 gives the right ratio 0 Using this AB value for one of the transitions read off across onto EB axis This gives you EB for this transition As you know E you can calculate B for the complex and you can then use this to calculate A EB 255 for the rst band suggesting that B is 665 cm39l This would give A 17950 cm391 Tanabe Sugano diagrams 9 d2 and d3 1A 1E 3A2 70 60 g n 7quot o 10 20 30 39 1 A235 3 AoB 0 Tanabe Sugano diagrams Old4 am 15 A2 A2 10 1G 3Pquot 5T2 is 50 T 1 l 1 i F A D a I n 340 2 I G 1 g 2 1 3E 3039 IA ads I H 2039 E 3912 1039 I E 136 5 53 E 3T 1o 30 f ADB 4 d39 with c 44775 4 A1 E I H IA quotE F 2A1 Tanabe Sugano diagrams 9 d6 and d7 3A1 A2 1A1 1o 20 AoB 30 39E 1 39quot E E 32 A 39T2 is 5T rga 39I 5 T t 28 3T2 3T A z 10 2 A 34 A2 AZIIQZA T 3 thze 2mg Tanabe Sugano diagrams d8 70 1A 11392 1E 3T1 60 1s a s 2 Aztze Highspin lowspin transitions and Tanabe Sugano diagrams 9 Note that the abrupt change in slope at about AB 22 occurs because the ground state changes from 4T1 to 2E and everything is plotted relative to the energy of the ground state This is a highspin to low spin transition occurring as the ligand eld strength is increased 70 2A 3 4 2 A2t2 2 25tge The nephelauxetic effect O The Racah repulsion parameters for a metal complex vary as the ligand is changed As the complex becomes more covalent the electrons are to some extent spread over the ligands so the electronelectron repulsion is reduced This reduction is repulsion as covalency increases is called the nephelauxetic effect literally cloud expanding O A nephelauxetic series can be set up based on 3 the nephelauxetic parameter B BComplex Bfree ion F39gtH20gtNH3 gtCN39gtB1 This series is consistent with uoride complexes being the most ionic and bromide complexes the most covalent Distortions 0 If a complex distorts from regular octahedral geometry this will show up as extra bands or shoulders on bands Perfectly octahedral TiH2063 should only give one dd trans1tion Band has structure indicating distortion due to the J ahn Teller effect Geometry changes to eliminate the degeneracy of the 2T2g ground state 5 Tiquotd39 E 0143MTiCla O llllllllllllllllll lililll lL39 5 10 WM 35 u Charge transfer transitions O In addition to seeing transitions between states that are essent1ally based on metal dorb1tals you can get trans1t1ons that 1nvolve 11gand based orb1tals and metal dorb1tals Called charge transfer CT transitions as an electron is transferred from the metal to the ligand or viceverso Charge transfer transitions often change in energy as the solvent polarity is varied solvatochromic as there is a change in polarity of the complex associated with the charge transfer transition gtgt This can be used to distinguish between dd transitions and charge transfer bands 138 A summary of the chargetransfer transitions in an octahedral complex MLCT Ln LMCT LMCT LMCT O Ligand to metal charge transfer LMCT bands are responsible for the colors of species like CdS and MnO439 O The energy of a charge transfer band depends upon the energy gap between the metal acceptor and ligand donor orbitals this is a function of the metal the oxidation state and the ligand OEnergies MnO439 lt TcO439 lt ReO439 Optical electronegativities o The energies of the ligand and metal orbitals involved in a CT transition depend on the electronegativity of the ligands and metal So the energy of a charge transfer band depends upon this difference in electronegativity For a species such as CrXNH352 see below The energy of the LMCT band will change as the halide X is changed A LMCT 7 75 5 i 1 quot d d 2 0 i i 138 A summary of the chargetransfer 1500331 saggim moan transitions in an octahedral complex In The zbsorplion smuum m CrClNH3 in mm in me visible m uimvmm kgmnx m peak covmpon ing m m tvansilion zEuA s not visible at this 39 mignl mliun Optical electronegativity 2 0 As the energy of a charge transfer band depends upon the difference in electronegativity between ligand and metal we can de ne optical electronegtivities based on v N C Xligarid Xmetal gtgt C is a constant chosen to give values for X that are approximately the same as the Pauling electronegativities Note we have separate Iable 13A Uphia L l tt lHJNE BElVIEItS values for 7 and o Metal Uh rd ligand 7 7 n a mm is m p H F x This is because the 5 i mm 23 L 3 34 symmetry ligand based 39Jijlll 3 1 Br 3x 11 mm 1 31 i I 5 3 orbitals are lower in a w 2 M10 35 energy than the TE al L l 2 NH 1 l symmetry lone pairs on im in v u Aw5 w m these ligands see Fig 138 MLCT transitions O Complexes that have ligands with low lying 75 orbitals often show MLCT transitions 0 They are very common with complexes involving bipy and phen MLCT absorption 3MLCT emission 1quot r Absorption 400 500 600 Anm 25 000 20 000 18 000 mquot m mquot 1311 The absorption an d phosphorescence spectra of Ruhipy3 6 Hurbipyiaizt 138 A summary of the chargetransfer transitions in an octahedral complex Resonant Raman O The nature of the ligands involved in a charge transfer transition can be elucidated using resonant raman spectroscopy If the incident laser frequency is chosen to be coincident with the charge transfer band energy resonant the intensity of some of the raman active vibrational modes is enhanced gtgt The vibrations that have an enhanced intensity are ones that involve motion of the ligands associated with the charge transfer transition The above resonant Raman data shows that both the phenanthroline and the CO ligands are involved in a MLCT transition for the above complex as vibrations for both of these ligands gain intensity when the Raman spectrum is collected on resonance Raman spectroscopy 9 Laser excitation source is used Intensity of inelastically scattered photons is measured 5mm 3 mm m nmuw lumian mm Mnnachmmnlm wmal39 mumM m exmlrd 5mm qu lhr mum at m mm m a mm mm m H mm pmmmm m annn sprrlmynm m Trans1tlon 1ntens1ty 9 Not all electronic transitions in coordination complexes have equal intensi 7 Charge transfer bands are often very strong m 2 1000 50000 L molquot cmquot 7 Transitions involving nal and initial states With different spins eg Mn are very weak a lt l L mol391 cm39l for rst row transitions metals and weak for heavier transition metals 7 dd transitions are intermediate in intensity trosymmetric complexes 2 20 100 L molquot cmquot 50 L molquot cm gtgt cen 2 nderstand these differences gtgt others 2 Q How do weu Selection rules spin 0 There are quantum mechanical selection rules governing how probable intense a transition is going to be 9 As photons do not have spin they can not in general induce transitions that involve a change in spin S Hence transitions that involve a change in S are very weak spin forbidden 7 However this rule can broken if there is strong coupling between orbital and spin angular momentum spinorbit coupling and for heavy elements this coupling is large leading to some intensity for spin forbidden transitions Selection rules Laporte O The intensity of a transition depends on the symmetry of the 0 states involved For centrosymmetric species free ions and octahedral complexes 7 g 9 g transitions are forbidden u 9 u transitions are forbidden u 9 g and g 9 u transitions are allowed The above rules are the Laporte selection rules This means that all dd transitions in octahedral complexes are formally forbidden as they are g 9 g gtgt Hence all dd transitions in octahedral complexes are weak For tetrahedral complexes there is no center of symmetry and this selection rule does not strictly ap 1 gtgt d d transitions in tetrahedral complexes are typically stronger than those in octahedral complexes Why does symmetry mater 0 For a transition involving the absorption of a photon IR optical etc there must be a change in dipole moment on oin from the round to the excited state This occurs when the fol owing integral as a none zero value PI and 1412 are the ground and excited state W1 ljzd Z wavefunctions u is the dipole moment operator and the integral is over all space This integral can only be none zero if the function being integrated has a component With symmetry like that of the highest symmetry irreducible representation of the molecules point group As H transforms like the functions X y and z u symmetry for a centrosymmetric species this in practice means that you only observe a transition When PI and 1412 differ in symmetry With respect to being centrosymmetric g or anticentrosymmetric u as the overall product 1411 uwz must have g symmetry Selection rules CT bands OAS long as a charge transfer band does not Violate the no change in spin rule it is likely to be very strong as there no other demanding restrictions on its occurrence Vibronic coupling 9 If dd transitions in centrosymmetric complexes are forbidden by the Laporte selection rule why do we see them 7 Complexes undergo vibrational motion Some of these vibrational modes can distort the complex so as to remove its center of symmetry 7 Coupling between modes that break the center of symmetry and the electronic transition leads to the transitions being weakly allowed essentially we excite the complex to a final state that is both electronically excited and vibrationally excited in such as way that the vibration removes the center of symme ry gtgt This interaction is called vibronic coupling gtgt Vibronic coupling leads to the rather broad nature of most dd transitions o You excite into a range of different vibrational levels and this range of levels adds breadth to the transition Luminescence OWhen a species is excited by absorption of a photon it can loose energy by nonradiative decay radiative decay luminescence 0 There are two types of radiative decay uorescence spin allowed emission phosphorescence spin forbidden emission O Luminescent behavior can lead to technological applications Lasers and phosphors Ruby Laser O The rst optical laser to be developed was based on luminescence from Ruby crystals Ruby is Ale3 doped with Cr3 Transitions associated with the octahedrally coordinated Cr3 are responsible for the laser action Poplulation inversion is achieved by exciting to 4T2 or 4T1g Internal conversion and intersystem crossing leads the population of 2E states These are long lived as ra iative decay to the ground state is spin forbidden Putting the crystal in a laser cavity can lead to lasing from the 2Eg to 4A2g transition T1 23 39 Internal conversron ng 39 lntersystem 9 EnergyeV Violet absorption Green absorption Red emission 4 A29 1310 The transitions responsible for the absorption and luminescence of Cr3 ions in ruby Lanthanide compounds O Lanthanide compounds are widely used as phosphors long lifetime luminescent material 9 The spectra of lanthanide compounds are very similar to those of the free ions as the ligands interact very weakly with the f electrons Very small ligand field splittings O This leads to weak transitions and bands that are very narrow weak vibronic coupling Get rather pure colors along with pastel shades Absorption 20 600 30 600 Wom 1 10 600 1312 The spectrum of the f23H Pr3aq ion in the visible region The Cotton effect 9 The Cotton effect includes Circular Dichroism CD and Optical Rotatory Dispersion 0RD O 0RD is the change in optical rotation from a chiral species as function of wavelength 9 A CD spectrum gives the difference between the absorption coefficients for left and right circularly polarized light as a function of wavelength 7 CD spectrum only exists for chiral species The polarization of light 9 Electromagnetic radiation can be polarized 7 either in a plane y gtgt Used for measuring 0RD 39 e or ellipticallycircularly gtgt Used for measuring CD spectra ma leh upper and quotgm lowcrk circularly polarized rumpnnent uf kctmmagntnt radvahmh 0an Mr mun mm 15 shown Use of CD and ORD spectra 9 CD and ORD spectra can be used to identify which enantiomer of a chiral species you have Compounds with similar structures give similar ORDCD spectra if they have the same absolute con guration 0 CD and ORD spectra can provide slightly better effective spectral resolution than an absorption spectrum and can be used to aid band assignment The CD spectrum of Coen33 a 0 The CD spectra suggest the presence of another absorption band at 24 20 000 24 000 28 000130 000 34 000 17cm cm391 that is not obvious from the absorption spectrum 1314 a The absorption spectrum of Coen33 and b the CD spectra of the two optical isomers 39 Assigning absolute con 9 Tris chelate complexes prepared using the amino acid alanine exist as two geometrical isomers both of which are chiral O The absolute con guration of the optically pure alanine complexes can be assigned by comparing their CD spectra to those for optically pure Coen33 Note the absolute configuration of Coen33 had to be determined first for this to work guration lui I a 39I I I I It I 39 II 39 39 I a who 39u u u 3221 J I39H R s r 39 4 r39 39 axw 3 R I I quot a 20 000 24 000 28 1001 30 000 34 000 30 000 We rn391 1314 la The absorption spectrum of Corfenjis1 and lb the CD spectra of the two optical isomers CD spectrum for Coedta39 4N NF 3c 39 Absorption cm391 300 200 I3 100 E AsL mol391cm391 N O v 4 16 20 24 28 171000 cmquot 1316 The absorption and CD spectra of 546Coedta39 referred to in Example 136 Assign as A based on comparison with Coen33 CD spectra iii 039 oquot o39 20 000 24 000 28 000 30 03900 34 000 173mm 1 3 E 1314 a The absorption spectrum of Coen33 and bl the CD spectra of the two optical isomers Relationship between ORD and CD O ORD and CD spectra are 7 related to one another quot39 mathematically Maxima in the CD spectra correspond to rst derivative like shapes in an ORD l spectrum of the same species ORD spectra for cobalt complexes O ORD spectra can also be used to assign absolute con guration by N Nltltn comparison with reference quot N quotw jjcg compounds f quot T r quotis Note that these spectra 39 Z emphasize the importance 39 E of specifying your 396 m m m 3 m m m wavelength when you talk um mm m I a c about a Slmple Optlcal Fig 1725 The absolute con gumions and mm specm arm A lcuenmquot m ACMS a121 s m union 0 S LHJaninei c AlC enhtS glnn Sglu Ihe di 39 r rotatlon measurement somch acid All or Ihcse complexes have me A or n con gumiun amquot a EPR or ESR spectroscopy 9 Electron spins behave in a similar way to nuclear spins when in a magnetic field You can ip the electron spin magnetization if there is any SgtO using radiation and do EPR electron paramagnetic resonance which is the electron equivalent of NlVIR 9 Typical frequencies of ESR transitions are much higher than those for NlVlR transitions 9 GHZ for a 03 T magnetic field Transition energy is given by AB g uBB B is the applied magnetic field uB is a fundamental constant g 20023 for a free electron it is a kind of chemical shift for the electron Hyperfine structure 0 Nuclear spins in a compound can couple to the electron spin 7 Coupling between electron and nuclear spins leads to splittings effectively because the nuclear spin changes the magnetic eld experienced by the electron l gtgt hv guBB AmI 1 proton gtgt A coupling constant measures strength of coupling O Coupling only occurs if the electron spin is delocalized into 2mm the part of the molecule where the nuclear spin is located 3 pm 0 Simple example for SiH3 radical aelectron on the silicon can couple to all three protons leading to a quartet 7 4 29Si 1 12 also couple giving pairs of satellites around the quot5 main pe s O The strength of the coupling value of Acan be used as measure of how delocalized the electron is 1 Th gnaw on hyper ne 7 For CuII complexes the following values of A coupling mm W 5quot SIPWU39quot 0quotquot 5 V39 radical SiHJi The origin of the lines Is between Cu and the electron spin were determined for damn iquot the wt different ligands ILigand H20 02 s2 IAmT 9898 85 l69 Magnetic eld gt Coupling constant drops as the electron is better delocalized off the CuII Complex example of hyper ne splitting 0 0 cu N Nw H H H H 8 Eislsalicylaldehyde imine copperlll 0 63Cu I 32 14NI 1 0 Basic spectrum has 4 lines due to coupling with Cu Each line is further split by coupling to 14N and H O Substitution of NH with D does not change spectrum No delocalization onto N H O Substitution of CH to give CMe does change the spectrum Collapses to 5 lines in each component due to coupling with two equivalentl l 14N Indicates delocalization onto CH groups 39 decreasing gt 1318 The EPR spectrum of copperlll bissalicylaldehydeimine diluted 1200 with the isomorphous nickell chelate The copper is isotopically pure copper63 The strong absorption at applied eld on the left is a radical marker DPPH used to calibrate the spectrum As is common in EPR the spectrum is displayed as the rst derivative of the absorption with respect to applied eld so each line has a shape like that of the strong DPPH absorption Bonding and spectra in MLS species 0 An understanding of the bonding and spectra of a complex with ML5 stoichiometry can be gained by thinking about what happens when a ligand is removed from an octahedral species pkgL L L L 1319 An orbi1a correlaliun diagram fair the lL L L m L l t L I L e or CuLb1 9 a 2 Lu He 5 sh own conversion of an ML octahedral complex into an Ml5 fragment Onl39y39 lhc frontier orbitals are Shape of ML5 species O The shapes of ML5 complexes can sometimes be predicted by considering an orbital correlation diagram Note that we would predict a at base square pyramidal geometry for species with 6 d electrons or less but some distortion once the dz2 orbital becomes occupied 10 d Lyg JV 171 a b c E l a 11 a l l I L 112 e 12 dmdy 71 dx b2 l l 93 100 110 120 a 1320 The correlation diagram for the metal 4 orbitals in an MLS fragment as the basal ligands bend away from the metal and the angle 4 increases from 90 to 120 The arrows show the location of la lowspin d oxyhemoglobin b low spin d3 NiCN53 and lc a d tetradentate macrucyclic complex of Cull with an axial CO ligandr Mixed valence compounds 0 Mixed valence species are often encountered in both the solid state molecules in solution 11360123 NH3 15 H3N FLUN 3 NHS HN N N NHS 3 NHa HaN I NH 12 RuleHalmlpyzlf Mixed valence IIIII Overview of Metal Chemistry Angus Paul Wilkinson School of Chemistry and Biochemistry Georgia Institute of Technology Topics to be covered OAn overview of the properties of the metallic elements 0 s metals 0 d metals Op block metals of block lanthanides and actinides The occurrence of metallic elements U 91 The msmhuunn a mum elements shown ham m me yuludic um Enthalpies of vapo zation 12 m nmzlplcs nl vapu mm m kxlujm 5 per male 15 m mum lzmtns m me p m mll quotMacks Reactivity 0 Most metals are reactive towards reagents such as oxygen 0 The noble metals Au Pt show no tendency to react with oxygen and are generally of low reactivity 0 Reaction of a metal with a reagent can produce compounds that still display metalmetal bonding Examples of metalmetal bonding O Rb902 Cs4O OReCl3 MoClZ ZrCl O FeZCO9 Occurrence of cluster formation vnsnnmnlalhc I chmm N a 1 mm mm Mnlal mm my Hm r W araccepmr quotWe immune Mm g4 mmmeizmnmusummmg mum39s Note that mm is m m mm um um i u m c mm mm mm Mmgusan m Wll imamquot in mmquot tummy manic Hall Engkwaud cum 195m 1 i a S block metals 9 Very reactive 9 Compounds tend to be ionic 7 much of their chemistry can be explained using the ionic model 9 Do not form a wide variety of complexes 9 Their chemistry is predominantly that of species in the group oxidation state Complexes of sblock metals 0 Complexes of alkali and alkaline earth cations are restricted to polydentate ligands 7 crown ethers 7 cryptands 7 EDTA and its relatives Redox properties of sblock Lt g e 0 Standard electrode potentials are quite uniform 0W decrease invaporization c519 e and ionization enthalpies is counter alance by a decrease in hydration 452 955 Table 92 Standard poienuals lor tbs x hlack omens EaV Cstg Gmup I 670W 2 Z LE 731 z 7 97 5515 Na 7271 Mg 7235 24 K 7294 c 72147 C W Rb 7232 Sr 7290 s aq 4 e c 73 05 Ba 7292 L lam a Note that lithium is widely used in the fabrication of batted es Why Crown ethers and cryptands 0 of axe I Q a E f KNd LEVNV 3222 crypt 2 221 crypt O 1 18 crown 6 The macrocylic chelate effect O The efficient binding of chelating ligands is typically argued to be a consequence of entropic effects 6 Chelating ligand displaces several monodentate ligands 0 With macrocyclic ligands there is a thermodynamic advantage over more open chelating ligands that is enthalpic g 25k l2 N Na39 K 351 I A mu 4 if n on it I M I 1 2 a u sun 4 74 A l h H 4 f In T in r 1 K IX 4 19 r L T J U 39n n a J 1 i ll 39llmril xk R I Lxlvll l39 yum Munun Jvmwrx m mm H moi Size selectivity 9 Crown ethers and cryptands show quite high selectively for ions that fit the ligand well p 222 crypt D Yenpl O a Li39 Na39 K39 Flb J 11 13 15 17 19 rA 97 lhc stabmty of complexes of melazs wrlh trypland ligands shown as a pm of mu logamhm I the umumquot rummnt m wntrr versus cation radius Note that me smaller 392 777 crypt favors complex lnrmauon wuh Na39 and me Fun 77 7 crypt favors X39 Suboxides O A range of alkali metal oxides can be prepared that have the metal in oxidation states of less than one They are often electrically conducting and can be Viewed as materials where 0239 is occupying holes in a metallic structure Liquid ammonia solutions O Dilute solutions of Na in liquid ammonia are blue ONaS NH3gt Nam e39m O The color is due to solvated electrons 9 More concentrated solutions take on a metallic appearance 9 The solutions are metastable Solvated electrons can also be produced in water based glasses by irradiation but they are not as stable Color centers O Electrons can also be metastably trapped in solid matrices 7 Called color centers 9 Irradiation of salts With Xrays or other ionizing radiation produces colored defects The color of the defect depends on the nature of the host lattice I l K h KCl KBr N acl L L 39 39 The wnn 39 by using electron in a box arguments As the box gets smaller the energy 1 CA Jul Luci I lU 4 6 Alkalide ions 9 If alkali metals are dissolved in alkyamines alkalide ions M39 are formed 7 The color of the solution in only dependent upon M39 That er cation does not mat Q Alkalides can be isolated if the counter cation is complexed with a cryptand 7 Na222Na39 Electrides Q It is possible using macrocyclic ligands to prepare electrides from solutions of alkali metals 7 Csl8C6Zquot e39 9 An electride is an ionic solid where the anlon IS 95 Aquot om may a M W xxmcmv 01 BUErnmwnG r39 quot1 an electron mm um mark m we all m r mm anan and m mam In The transition or d metals 9 Extraction of the metals 9 First row versus heavy transition metals 7 Stability of high oxidation states 7 Coordination numbers 9 Oxocomplexes O Polyoxometallates 9 First row versus heavy metals 7 Low oxidation state compounds Extraction of the metals um Ru l n Du39wm cm than rm m umwwm Muwmr Mnk mus nut quotin mm m rilh MnUJ 2r r m w in mm rin own wn L H Wme xMulWLMz lulhmm Whip qlhlt7 v lim ll mm w mm m Mu m m M liNyvll39Clr v w m Mynvomzr 0 mm m 1mm WWW mm in mm its ms m lt m Au m rm mummn mx mm m i an 4 mm m mu m First row metals versus the heavy transition elements OThe chemistry of the 4 and 5 d metals is similar 0 The first row TMs differ from the heavy metals 3 d metals often have oxidizing maximum oxidation states the heavy metals often display metalmetal bonding when they are in low oxidation states 3 d metals often show lower coordination numbers than their heavier brethren Trends in size O In going across a transition metal row ionic radii tend to decrease O In going down a transition metal group ions of the 3 d metal are often much smaller than the 4 and 5 d ions the 4 and 5 d ions are frequently similar in size Ionic radii of the 3d metals Fig 15 Radii of the divalen a above and the trivalen ions 0 C T Acta Cryst 1970 826 1076 Ionic radii down a group O Tetrahedral CrVI 40 pm MoVI 55 pm WVl 56 pm 9 Octahedral TiIV 745pm HfIV 85pm ZrIV 86pm 0 Square planar Nill 63pm Pdll 78pm Ptll 74pm 9 Low spin octahedral CoIII 685pm RhIII 805pm IrIII 82pm 3d metals in high oxidation states 9 Typically oxidizing power of highly oxidized species drops on going down a group High oxidation states for heavy metals are often quite stable 5 6 7 1 2 3 4 Oxidation number N 911 A has lzgrzm for the 1mm gruup m the dblunk Group 6 m acidic solution pH ov The maximum possible oxidation states for the halides of TMs 9 Note that the group oxidation state is only achieved in the early part of the transition block Higher oxidation states are o en achievable With the heavier metals 4d 5d 9 Fluorine o en facilitates a higher oxidation state than other halides 9 Table 94 Highcsi oxidation stak rlrblock bmary haimes39 Group 4 5 6 7 B 9 I0 I I iii VF my Mum RBI Cor1 NIF ciitii2 zii MaiS MoFB TcClE RuF we m AgF Hll Tag warE w oars lan m5 AuCIs 10 mars for wvcml days 1 mom Icmp awk m a passivakd Monti caniaincr Fluorides and oxides 9 Several metals only achieve their maximum possible oxidation state in oxides 7 0504 is readily prepared but there is no corresponding uoride 7 W0439 exists but there is no corresponding uoride 7 CrO4239 is easily prepared but CrF6 is difficult to prepare and is not very stable Variation in coordination number on going down a group Q The coordination numbers heavy metal complexes are often greater than those of the 3d metals Table 95 Coordination numbers of some tavly dblock fluoru and cyan Cnmplrxzs Complex coordination numhtr rm graup 3 4 5 1d NHngSch 6 NaleiFsJ 6 KlVFsl 6 KzMCNleZH20 7 M W a 9 Naallrhl 7 Klethl 7 KslNNCNJsl 8 54 Namfg 9 NialeFyl 7 KJITBFE 8 Aquo ions O Aquo ions of 3d metals are common 0 Aquo ions of the heavy TMs are rare 7 PdOH24 RuH2062 Oxocomplexes O Metals in high oxidation states particularly at high pH tend to form oxo or hydroxo complexes ra er than aquo species 7 MnOA39 CrOAZ39W04139 VOL 9 Oxo ligand effectively has a double bond to the metal There is considerable 7 interaction between the metal and ligand 9 It is quite common to nd the site trans an oxo ligand to be vacant or occupied by a we y bound ligand due to this 7 interaction Oxocomplexes of Ru O Pourbaix diagram shows 7 high pH favors conversion ofan aquo ligand to a hydroxo ligand and conversion of hydroxo to oxo 7 Increased oxidation state favors conversion of an aquo ligand to a hydroxo ligand and conversion of hydroxo and oxo W 1 fll lt5 m s rllRuLCll Nlll rMRuW IDDLCIll39 mmmroncu39 m lmt Ltnoupr a n m A Puuvhmx mm la n W mum M mm M0 in mm L Mm m w W m 6 u n 39 W m m xrv Wm H mm mcw MM Mm m unrwu m was ussvll Polyoxometallates Q Oxo species of the early 4 5 5 7 transition elements often 1 WWI crtvl Mn undergo condensation reactions at low pH to form Zr NblV Mist Tc Hi Tam WM Re polyoxornetallates 2 s s Elcmrms in nn new uni form crO4 2H quotquot39gt pniynxnmexsuntrs The shaded eimnem 2 term we mam may 2 Cr207 H20 pniynxnmmnaus o 6MoO4239 10H M06019239 SHZO Examples 7 7 1a lanoyi s u WUBWiDNhlw Not only comer sharing is found for polychromates built from tetrahedra but edge m shining ofpolyhedm is OK 0 M0 an W built m in mi from octahedra This is due to distance between W quotawn n m m MD Heteropolyanions O The polyanions produced on condensation can incorporate nonmetal species such as phosphorous and silicon in which case the resulting clusters are referred to a heteropolyanions 1 5 PM0120401339 Low oxidation state cations of the 3d metals 0 Low oxidation state ions of the early 3d metals are either strongly reducing or unknown T12 Ti3 V2 Cr2 O The 11 oxidation state becomes increasing more stable on going across the row Low oxidation state ions of the heavy transition metals O The early heavy transition metals do not form simple compounds with electronegative elements when they are in a low oxidation state 7 ReCl3 is metalmetal bonded 9 Low oxidation states IIIII become progressively more stable on going across a row Metal metal bonding 9 Many low oxidation state compound of the heavy transition metals display metalmetal bonds 9 For the earlier metals these compounds usually involve 7t donor ligands like halide or alkoxide O For the later metals 7t acceptor ligands are usually present CO PR3 etc Sheet and chain structures 9 ZrCl and Sc7Cl10 917 The structure of 5cm x showing the 918 The structure of ZrCI c0n5Ists of single Chain Oneammsat W W and layers of metal atoms in graphite like multiple chains at the bottom From JD Corbett Acc Chem Res 14 239 hexagonal nets 1931 MoCl2 and it s relatives 0 MoCl2 contains octahedral 2 clusters of molybdeum m This motiff is found in variety of compounds F39 mu 1 22 Msxuli39 represenulium nflhc Mason chum and Lh 0323 Can be produced Mom m WELL from MoCl2 by hum o reactlon Wlth HCl chlorine Atoms to s layer in Note faces are capped Part of MoCl2 structure Chevrel phases 0 Similar face capped octahedral clusters are found in a family of chalcogenide materials called Chevrel phases PbMo6S8 etc Fig 11 Association 139 M0558 clusters In the C E phase PbMossa Nb and Ta clusters Halide X 9 Edge bridged clusters l M Ta x KH M E rather than face xx capped with the fgkf formula M6X182 are Eigm x found for Nb and Ta X7 X 23 Mexmlz ReCl3 Q RcCl3 is a metalmetal bonded compound containing Re triangles 7 Discrete Re3Cllz339 triangles can be produced by treatment With Cl39 919 the suucturc at ml m m sulld stak in mm hands mrrcspnnd n Intcmctmn mm a Cl mm mlnngmg m an adjacent clusm ReZClgz39 OClassic example ofa species with a quadruple bond CI CI 72 5 cu cu a 104 15 RR Re I l Cl Cl Cl Cl Z 18 ReZCIB 0 a WM Other metalmetal bonded dimers Can achieve a wide variety ofbond or ers Nobel metals 9 Not readily attacked by aqueous H4r 7 Dif cult to oxidize 9 However there is an extensive chemistry of these elements 7 Dangerous to assume quot392 I mmals they are truly inert 921 The location of the platinum and cuivmgv m als m m periodic table Nobel metal complexes 0 These metals occur in a variety of relatively low oxidation states 0 Many of their d10 complexes are linear 0 Many of their d8 complexes are square planar Metal sulfides O The transition metals become softer on going from left to right across the periodic table OPolysulfide species are quite common 9 Highly oxidized metal cations do not occur as sulfides FeS2 is an FeH compound Monosul des Table 910 Structures of d block MS compounds Group 4 5 6 7 B 9 10 Nickelarsenide structure shaded 1T3 39 Mn l Fe C39CL Rocksalt structure unshaded Zr Nb Metal monosulfides not shown here for Group 6 some of the heavier metals have more complex structures TMnS has two polymorphs one has a rock sait structure the other has a wurtzite structure SourcesAf Wells Structural inorganic chemistry p 752 Oxford University Press 1984 Disulfides Table 911 Structures of d block MS compounds Group 4 5 6 7 8 9 10 1 I Layered shaded Fe Co NI Cu Pyrite or marcasite Ru Rh unshaded 1 Us Ir quotflats quotMetals not shown either do not form disulfides or have disul des with complex structures Source AF Wells Structural inorganic chemisml p 757 Oxford University Press 1984 The pyrite and CdI2 structures 925 m swam of pyrie 5 9 24 the db Shunuv mum by man msul dns me 1mm hav adjaunl sul dc lavas m pm of m l atoms Applications of layered disul des O MOS2 7 used as a lubricant 7 used in desulfurization CoMoSzAle3 O TiS2 7 battery electrode material 7 xLi Tis2 LixTiSZ Group 12 11B OThe elements Zn Cd and Hg are not classified as transition elements as there is chemistry does not involve valence d electrons OThese elements are not Noble like their neighbors due to low lattice energies Redox reactions OZn and Cd are reactive compared to their neighbors Cu and Ag Zn2 076V Cu2 034V Cd2 040V Ag 080V OThe chemistry of Zn and Cs is dominated by divalent cations OMercury has a significant chemistry in both I and II oxidation states Hg22 O Hg is a metalmetal bonded species 0 Mercury 1 can be easily persuaded to disproportionate Ongztaq Hga Hg w K 6 X10393 0 ngzaq ZOH39WD gt Hg HgOs H200 The p block metals O HeaVier pblock metals often occur with an oxidation state 2 less then the group value 7 This is the Inert pair effect Pbo2 NEeV NEGv Pb o Snz Sno D V quotV 7 39 o n 2 3 4 Oxrdalmn number N Oxidation number N 93925 Fmstmagrm Vernc quv allquot 927 valdiagvamsf rtht mup uw ubluck mums w some mlmmn quotrum mutils in audit sululinn Group 13 111A oAluminum chemistry is dominated by an oxidation state of III 9 Gallium and indium form compounds showing both I and III oxidation states InI and GaI are reducing O Thallium forms compounds in oxidation states I and III T1IH is oxidizing MIII chemistry OMX3 M B A1 Ga X Cl Br I are Lewis acids OFor hard donors the Lewis acid strength is Bx3 gt Alx3 gt Gax3 OFor soft donors the Lewis acid strength is Gax3 gt Alx3 gt Bx3 MI chemistry 0 Ga and In form a number of mixed valent and low oxidation state compounds GaCl2 is GaGaCl4 0 However some Gall compounds have metal metals bonds GaS and TMA2C13GaGaCl3 O Tll has some similarities with both KI and With Agl TlX X halides insoluble TlOH soluble Tin and lead chemistry 0 Both metals form compounds in oxidation states 11 and IV 0 Sn II is reducing in aqueous solution 0 PblV is oxidizing O MII compounds often have a stereochemically active lone pair Stereochemically active lone pairs Sn Cl CI CI 32 SnClar Bismuth O Bismuth chemistry is dominated by BiIH O BiV is a powerful oxidant OBi3aq 3e39 gt Bis E0 032V O Bi5taq 2639 gt Bi3taq E0 N 2 V O BiIII compounds often have stereochemically active lone pairs Factors favoring distorted geometries 0 Low coordination numbers favor a stereochemically active lone pair BiF3 and SnCl339 O Lighter elements show a stronger tendency than their heavier relatives to be distorted Sb gt Bi 0 Small ligands favor the presence of a distortion F and alkoxides rather thanl Lanthanide chemistry O The lanthanides are technologically important 9 Their chemistry is simple dominated by the 3 oxidation state the M3 ions are hard Overview of lanthanide properties Tahl 914 szgs svmbois and pmptmts cf m unmanms z 3333i 22 23 Nam Lamhanum Canum Praseudymium Neuuymmm Promclhmm Sa Svmhul E Canngumiun or M E av 230 rMquotK NI AA F7 gt9 n 3 3D 3 unmauquwumugyy a 39lnnlr vadu lo CN 3 from RD Shannan Arm ErysmHoyr A32 75 15761 a and nonaqumus Kn mm are aisu mum tn Applications of lanthanides 9 They are widely used in ceramics synthesis 7 High Tc superconductors 7 Conducting oxide electrodes 9 They are used in phosphors for devices such as TV sets 9 They are used in lasers 7 NdYAG Compare oxidation states of the lanthanides and actinides Symbol 2 3 4 Symbol I 2 3 4 5 639 i39i LII c k I III I I I P I I I I I d I I I Nd I I I I v I I I Pm Np I I I Sm I 1 I I I I Nu Am I I I I I I I in I m I l I I l l h i I I Bk in I I I I I I I I I IN Hu I I ix l39l I II I r P Fm I m I I MI I I Yb I Nu I Lu l I I IhhrcaIIIIIIIIu w IIl In Ulllllwlk I II Inuml In I Ild LIII IIIIII Iquot I L ilyquotIL run quotIn Hh dJHHILKC d HIIIII I rqIIIwnla live mmI ml lc IIzIdJIIIxII lI l 39III I IIIIIrhAmIlIx u 034 j I mm In I It 1 HF f t l NIIIHIIU L39k39 luv J J ll I k iml m i I In J N39IHHH III IF mu LfI mum K4112 J J Suburn i A39IIJ I IR I II n Pde 39hmpnmn and HIIH London l l lu quotIII 2 l39huplcr Id The lanthanide contraction Ionic ndjus pill 1 ll I0 ll 12 13 14 Number Ifelectron 3 Fig 145 Ionic radii CN 6 ofSc Y La Ln and An Ions Separations O Lanthanide ions are dif cult to means as there sizes and charges are so similar 7 Can separate elements that readily do to 2 or 4 9 Liquidliquid extraction used for large scale separation 9 Ion exchange chromatography used When high purity is needed gt Vulume M sluam Cnmmmmn 911 mum m in mm lanmamd mm H Complexes O The lanthanides cations are all hard and form complexes With hard donor ligands O The complexes o en have high coordinationan ers 10 and irregular geometries O Ligands interact very weakly With the electons 7 Crystal eld splitting is extremely 39gible O Complexes have some applications including NMR shift reagents CH3KCJk CFZCFZCF3 fod Actinide chemistry 9 Much more complicated than that of the rare earths O The early actinides can attain a variety of oxidation states Overview of actinide properties hm 5 15 Names swam m pmpzmd at my umus as 2 Mam Symhm numbu rfMJ 1X om Anmmm Ac 221 2x y I 25 x mm m 232 m x 10 quot y 7 a w Pmtammum Pa 23 mny 11 45 2 Unnium u 22 4mm m 34 m Ncplumum Np 231 2mm us 145 94 Ptulnnium Pu 244 lx my m 34 5 Amtm mm Am 243 uxxlmy m a Cunum Cm 2n usme Ill 91 BUR m Bk 247 1mm x m 3 A ax Camommm Cr 249 y m 3 99 Emsxem m 5 254 277m 107 a mevum Fm 257 mud 2 m Mendckwum Ma 25 554 mm 2 m2 Nondmm Nu 259 m 23 m is Vencmm u 60 1mm 22 3 my 0 M m must mwwm mick mm mmrmdu mch a him an 9 2quotme mmuayr m 75 my Emmam m yarcmhmalc mm W Bvurmm M imam uw 5m JV mm x Wm n m w quotmm at m A Hundusnn m in warmquot mm mm Am us 257 new 1mm an in aqueous mum m yvmummzm Maw mm is m mu Vzm39 rm sr 5mm and w mm The dunan banM1 mammm u 34 www inmmm NM m was Applications of actinide chemistry ONuclear fuel weapons material processing ONuclear fuel reprocessing 9 Nuclear waste remediation Stable oxidation states of actinides j L i LL gmmm 7 nunn NE w Aqueous solution chemistry of the actinides O The formation of 0X0 species is commonplace O U02 U0 9 Pquz PuOf O The nature of species present in solution is strongly dependent upon both pH and reduction potential Fission Q In a conventional nuclear reactor 235U nuclei capture neutrons This leads to the 235U nucleus splitting to give fission products a lot of energy and additional neutrons which can go on and propagate the nuclear Fisslan yield per 2an 1 mm 1 as reaction so so use 120 no 16v 150 I I Mass numbm A 7 FISSIOH products span a very 9 5mm mmmunun rm nu Wide range of elements windsme quotrimmm mmmn indumd 05mm nl quot U Flam 5 T Scalmrg and Wu mvklzn 1m mm mm ummum Wulgy New York man Mesoporous materials Overview Why mesoporous materials Self assembled templates and the structures that can be formed using them Control of pore size Mechanism of formation Absorption properties Why mesoporous materials Zeolites are limited to pore sizes of l 5A Materials characteristics similar to zeolites but with larger pores would be very useful 7 Separate larger molecules 7 Perform catalysis on larger molecules gtgt Crack higher MW hydrocarbons to form gasoline etc Self assembled templates offer a way to produce oxides with larger pores Self assembled templates In zeolitic materials the template is a single molecule or ion Self assembled aggregates ofmolecules or ions can also serve as templates 7 Surfactants aggregate into a variety of structures 115 depending on conditio L Mid r rm Self assembled surfactant structures In solution surfactants can self assemble to form micelles rods sheets and 3D structures 7 All of these can in principle be used as templates 7 Rod like surfactant aggregates have provided some of the most interesting structures A lot of work has been done exploring the formation of silicate structures using self assembled templates 7 Other inorganic oxides have also been examined Materials containing rod like assemblies Lamce Image 4 m Xray Dltlraclion Panern Possible Structure r lnlensily dU ml m H m n m 20 11 h mule K m 1 N H L quot J l I l 1 0 Degrees 24mm MGM41 silicate structures Material is highly ordered and gives a diffraction pattern but the silicate walls are not crystalline they are glass like A typical MGM41 synthesis MCM4l contains rod like surfactant aggregates MCM4l materials can be made in many ways Aluminosilicate materials have been prepared as follows 39 C16H33NMe3OH catapal alumina TMA silicate and amorphous silica stirred in water 39 Heated in autoclave for 48 hours at 150 C 39 Recover by ltration and remove template by heating in nitrogen to 540 C for 1 hour and then heating in air for 6 hours I Surfactant decomposes by Hoffman elimination reaction Pore size distribution The pore size distribution in MCM4l is usually quite narrow as well ordered materials can be made but it is not as tightly defined as that for a zeolite as MCM4l is not a crystalline product I 5 my 5 uA Scrptlon 39 5 1 Arbitrary I I Unit i 20 so Pore Dlameter A 3D porous silicate structures Lam quotquot395 Xray Diffraction Pattern Pugh 5quotquotc u39e Intensin L Wquot m m A T20 250 an m T m an m m m 132 m 7 l6 1 m y 1 v v 2 4 0 Degrees 2mm 3D porous networks can also be prepared Once again the silicate is glass like but the pores are ordered Lamella structures Xray Diffraction Pattern Possible Structures W am and mu 1 A 2m 9 a Slllca Sheets Intensny v5 20 2395 u 1 Damn 2mm Lattice Image A Variety of different layered structures can be formed These data apply to MCMSO a stabilized layered structure Unstabilized structures contain surfactant bilayers and collapse when the surfactant is removed Controlling the type of self assembled structure Changing the composition of the synthesis mixture can change the type of self assemebled structure that is formed CTAB A c cubic Ian H lhexa gonal 08 L ame ar 39 Fig 17 SyntheSisspace diagram of mesophase HZOS39Oz 100 structures established by XRD measurements Tetraethoxysilane TEOS was added in different concentrations to basic aqueous solutions of 06 CTAB such that each mixture overall had a H20 VA SiO2 molar ratio of 100 The mixtures were stirred V13 at room temperature for 1 hour before being heat ed at 100 C for 10 days Firouzi et al Science 267 1138 1995 Control of pore size All the early work on mesorporous silicates was done using MeCH2n1NMe3 surfactants Increasing the chain length produces materials with bigger pores Swelling the surfactant assembly by the use of an organic additive such as trimethylbenzene also gives bigger pores After a material has been made the pore size can be reduced by modifying the interior surface In uence of chain length Increasing the surfactant chain length increase the pore to pore spacing and the total fraction of the material that is open space 100 21 C Total Gas Flow 190 cclmin 80 C16 MGM41 12 39 60 C14 012 wt mom41 14 4o i MGM41 16 20 I 5 0 I I I I I I 0 1 15 0 1o 20 30 4o 50 60 70 Degrees Two Theta Vapor Pressure torr Pore size and chain length Surfactant Lattice Ar pore size Maximum chain length constant A A benzene 11 uptake at 50 CnHZHthMe3 torr wt 8 3 l l 8 l 6 9 32 21 3 7 10 3 3 22 32 12 3 3 22 3 6 l4 3 8 30 54 16 40 37 64 From Beck et al J Am Chem Soc 114 10834 1992 Swelling using auxiliary organics Hydrophobic Micelie Interior n 5 Auxiliary Organic I WI 39 J CH5 CH4 39 Hydrophilic Mesi lene Syvelled Exterior CH ty Mlcelle 75 15 65 I 55 I 60 60 XRD d m 55 I 55 Pore srze 39 0 by Argon s cm pa 9 so I 50 physlsorptlon 45 I 45 I 40 i l 40 as 35 30 I I I I I I I I I 30 o 05 10 15 20 25 Moles of MesityleneMoles of Surfactant Fig 6 Powder Xray diffraction d100 spacing and Horvath Kawazoe pore size as a function of mesitylenesurfactant molar ratio from 7 Post synthesis modi cation Silylation of hydroxyl groups in MCM4l using reagents such as Me3SiCl can be used to reduce the effective pore size Parent MGM41 394A 16 Silylated MGM41 12 304A Sorption 03 04 39 0 I I I 20 25 30 35 40 45 50 Pore Diameter A Fig 8 HurvathKawazoe pore size distribution for MCM741 having a pore diameter of 40 A and the silylated version from 7 Mechanism of formation for MCM4l Quite some controversy 7 Does the surfactant self assemble and then get coated in silica or does the interaction between the silicate species and surfactant play an important role in self assembly Hexagnnal Away Sunaclam Mmellar Mmelle am l x gtl g 3 gt 4 v 4 x quot MCMM 3mm Q m a Even layered intermediates have been proposed Some layered silicates can be converted to MCM4l like materials by treatment with a surfactant 7 Supports notion that there may be a layered intermediate in the formation of MCM4l 0 I39 9 4 Role of silicate Interactions between the silicate and the surfactant play an important role in the self assembly process Ordered structures are formed in the presence of silicate that are not formed in pure surfactant solutions under similar conditions Fig 2 Small angle neutron scattering data for a dilute 1 CTAB HZO solution with and without 10 W 11 3500 dissolved silica Filled circles inset outline the 2 8000 0 2500 5quot 391CTABinD0 scattering pattern in the absence of dissolved sil E 39 o 1500 I 2 tea which reveals a single broad peak indicative of E 6 000 spherical micelles The open circles indicate the 5 500 scattering from the precipitated phase that forms 2 4 03900 0 0 03905 01013115 0 20 0 25 when SiOZ NaOH in a molar ratio of 1521 is S 7 o o m i added to the solution This phase exhibits a dii 2 23900 o o 1 fraction pattern characteristic of an ordered hex g 7 Rawquot agonal array of rodlike aggregates with a d spac E 0 0 1 3 0 4 O 5 ing of 45 r 02 rim Gait1 o Firouzi et al Science 267 1138 1995 Mechanism involving silicate surfactant interactions Fig 4 Schematic diagram of the cooper A precursor solutions ative organization of silicate surfactant w M mesophases A Organic and inorganic 39 3910 39 0 392 D precursor solutions Depending on the 39 o quot o o D concentration of the surfactant the initial 39 3 39 39 g a 390 3 a 395 Pf139 4 organic precursor consists of spherical or Cyhndngal or37hPSOIdaD mlgenes that are In Micelles and isolated cailonic Inorganic silicate anions dynamlc equll39bnum W39th Single SurfaCtant surfactant molecules for example D4R oligomers molecules The inorganic precursor solu tion at high pH contains predominantly multiply charged silicate anions for exam B Ion exchange pie D4R oligomers see Fig 58 B lm mediater after the two precursor solutions 39 W 43b are mixed silicate oligomers ion exchange 39 39 with Br and OH anions to form inorgan icorganic aggregates whose structure can be different from that of the precursor micelles C Multidentate interactions of oligomeric silicate units with the surfactant molecules has several implications in par ticular the screening of the electrostatic doublelayer repulsion among aggregates can induce self assembly of SLC me sophases The processes of ion exchange and selfassembly appear to occur on comparable time scales HM or o 0 o o transformation H Lamellar SLC Hexagonal SLC Firouzi et al Science 267 1138 1995
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