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Download Metal-Ligand Binding in Transition Metal Complexes
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Crystalfieldsplittingsforhexa-auacomplexesofand3 2 + E onfiguration 0cm1 0kJmol1 +III Electronic 0cm1 0kJmol1 4 6 8 9 12600 (11) 12600 11 13900 (166) 800 93 10400 124 9300 111 800 102 1 20600 243 2 18900 226 3 1830 213 4 21000 21 1300 164 6 18600 222 8 –3 10 Dq [Cr(CN)6] +3 10 Dq [Cr(NH3)6] 10 Dq [Cr(dtp)3] t2g –3 eg 10 Dq [CrCl6] Relative energy Increasing ligand field strength Metal-Ligand Binding in Transition Metal Complexes eg t2g Eletrononiurationoa wkchdfd. yssgs Wk f 3 fu U S f FSE 3 3 3 3 1 2 3 4Dq 8Dq 12Dq Dq Dq Dq Dq Dq Dq Dq 3 fu U FSE 1 2 3 4Dq 8 Dq 12Dq Dq Dq Dq Dq Dq Dq Dq 3 3 3 3 CRYSTAL FIELD STABILIZATION: STRONG FIELD CASE eg t2g A Summary TETRAHEDRAL COMPLEXES Metal-Ligand Binding in Transition Metal Complexes dxy dxz dyz t2 D tet dx2 – y2 dz 2 dxy dxz dyz Free ion 2 2 2 e dz dx – y Tetrahedral field fu Nub f u FSE Dq Dq Dq Dq Dq Dq Dq Dq Dq Dq 2 x –y 2 z 1/2 d1 d1 1/2 d1 2 2 1/2 d1 eg 1/2 d1 10 Dq 2 z x –y M d1 2 10 Dq Z-out (elongated) (a) xy d2 2/3 d2 1/3 d2 xz, yz (a) xz, yz t2g 1/3 d2 d2 10 Dq M 2/3 d2 xy (b) Z-in (compressed) (b) 22 orbitalhasfourlobeswhilstthe2hasonlytwolobespointing attheligands.Tominimizerepulsionwiththeligands,thesingle 2 orbitals. This is euivalent to splitting the degeneracy of the 2isoflowerenergy,i.e.,morestable,and22isofhigherenergy, i.e.,lessstable.Thus,thetwoligandsapproachingalongthe H + A z2 2 2 x –y v1 v2 xz, yz xy Absorption 400 400 Wavelength –1 Relative intensity Frequency (cm ) 18000 15000 12000 10000 500 600 700 800 900 1000 1100 "Hole" "Hole" 2 2 x –y b1g eg a1g 2 x xy b2g t2g eg xz, yz eg b2g a1g b1g tal-ligandditancinCIIandnIIcompound 172 r2 4200 129 224 Kr 2200 129 4214 14 M 2179 108 2191 120 2209 18 M(H) 4188 115 220 157 CH2 — CH2 H2N NH2 bite H2 O N N N N Cu N N Strain N Cu + en N + 2H2O N N H2O 10 – pK 8 6 4 K1 2 K2 K3 0 Mn +2 +2 +2 Fe Co +2 Ni +2 Cu +2 Zn H2O N N Cu N N N N N H2O Cu N N N 2 x –y 2 x –y 2 2 10 Dq 2 z 10 Dq xy xy xz, yz Cu(II) z 2 xz, yz Au(II) Absorbance 400 500 600 Wavelength (nm) 700 2 2 dx – y dz 2 Energy dxy dxz dyz Ground state Excited state kJ mol – 1 3000 F 2900 2800 Cl Lattice energy 2700 Br 2600 l 2500 2400 2300 2200 2100 Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn 4800 2200 4600 2000 4400 1800 4200 1600 (a) M Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga 4000 2+ (b) M 3+ +3/5 – 2 /5 – 2 /5 – 2 /5 100 Ionic radii (pm) 90 ? 80 ? 70 ? 60 2+ 2+ 50 Ti Ca 1 0 2 Ionic radii (pm) 80 2+h 2+ Cr Mn 2+ 2+ 2+ Fe Co 4 3 5 6 7 Number of 3d electrons 2+ 2+ 2+ Ni Cu 8 9 Zn 10 70 60 3+ 3+ 3+ 50 Sc Ti V 1 2 0 V Cr 3 3+ 3+ 3+ 3+ 3+ 3+ Ca Mn Fe Co Ni 4 6 5 7 8 9 10 At this point the next electron enters the level, into an orbital directed at the ligands, repelling them and causing an increase in the effective radius of the metal. In the case of high-spin ions the increase in the effective radius of the metal. In the case of high-spin ions the increase in radius occurs with the Energy Ground state Excited state For , and orbitals. When one electron is excited, the resulting combination can have different energies, depending on whether the two electrons are occupying overlapping orbitals and therefore repelling each other. For example, the excited configuration of (), (), will be lower in energy because the two electrons occupy very different space, whereas the (), ( and planes. By calculation, it can be shown that the combination (), ( ), ( ), ( ), ( dz 2 Least Energy dxy Ground state Excited state dx2 – y2 More Energy dxy Ground state Excited state Most Energy Ground state Excited state 2+ (i) [Ni (NH3)6] . Octahedral 8 Ni is in + II Oxidation state, d system. eg 3d 10 Dq 6 t2g 2 The configuration is t2g eg . –3 (ii) [Cr (CN)6] Octahedral 3 Cr is in + III Oxidation state, d system eg 3d 10 Dq 3 0 The configuration is t2g eg . t2g 2– (iii) [Ni Cl4] tetrahedral – Cr is in + II oxidation state and Cl is weak field ligand. t2 3d 4 4 The configuration e t2 . e eg 0 t2g eg t2g eg t2g eg t2g eg t2g eedmpexeeeeypypempexebe e beeympedoctahral Hnc,th lctrons o not air u an follow Huns rul of aiu ultilicit e t = 4/9 0 + 0.6 0 – 0.4 0 t2 eed ..m ..3 1. ff = ( 2) Cr(0) eg Weak field < P 4 t2g eg 2 t2g In octahedral field eg Strong field t2g6eg0 0 < P t2g eg Weak field < P 3 t2g eg 1 t2g Octahedral field eg Story field < P 4 0 t2g eg t2g eg Weak field < P 3 t2g eg 0 t2g In octahedral field eg Strong field t 5e 0 2g g > P t2g eg t2g eg t2g Hypothetical complex with degenerate d-orbitals Five d-orbitals (degenerate) in isolated metal ion + 0.6 – 0.4 Energy eg 0 t2 g eg eg t2g t2g ssuing that light of onl on scific wavlngth is asor a coorination cooun, utili th following rlationshi of th visil sctru to trin Colour violt lu grn llow orang r q sc (iii) [TiX6] col is violt, what chang in colour woul ou ct if th ligan , in this col was rlac a ligan, , that roucs a strongr fil? (i) = = vogaros nur = 62 2 = Plancs constant = 66 2 rg sc = vlocit of light c sc = calori = rg Th nrg asor r ol is 2 cal or 2 rgs Putting th valu of , , an , w gt 2 = 62 26 66 2 rg sc c sc = 62 2 66 2 2 = 66 c Th colour asor is r an th col will grn in colour (ii) = sc = c sc sc = 66 c Th colour asor is violt so th col will aar llow eg Strong field t2g 6 Co (III) d system (octahedral) eg Weak field t2g eg Story field t2g Co (II) d system 7 eg Weak field t2g eg 0 t2g Conc. HCl or HCl t2 In a weak field (tetrahedral) t e d demeeeyepeeme ed e ed ppe mpexe ee e e e x d ed e ymme d eey ded. xp y configurationisaoctahralcol eg t2g eee 2 an 2 2 oritals ar unuall occui istortion (nown as ahn-Tllr istortion) occurs Th ahn-Tllr thor statsthatannon-linarolculsstinagnratlctronic statwillunstalanwillunrgososortofistortiontolowr its str an rov th gnrac an to lowr th nrg nanoctahralcol,istortionoccursainlfrounualfilling ofthbbeeeebeexee2b ebe eeexe. emmeep ed eepye2 oritalanonlctronoccuth 22oritalThus,thtwoligan along+ d de e epeed me y e e deededede. Energy eg t2g Metal-Ligand Binding in Transition Metal Complexes Diagraaticall rrsnt for th slitting of th oritals for th following gotris (i) Ttrahral (ii) Octahral (iii) Ttragonal (iv) Suar lanar Slitting of th -oritals for various gotris no (i) (iv) is shown low Ttrahral, shrical octahral, ttrahral, suar lanar slitting of th -oritals for th various gotris dx 2 – y 2 dx 2y 2 dz2 dxy dx2 – y2, dz2 Energy dxy, dxz, dyz dz2 dz1 dx2 – y2, dz2 dxy, dxz, dyz dxz, dyz Tetrahedral Octahedral dxz, dyz Square planar Tetragonal How an unair lctrons ar thr in Cr2+, Cr+, F2+, Co+ an Co2+ in (i) a string octahral fil an (ii) a wa octahral fil? nair lctron in th ions in (i) strong an (ii) wa octahral fil ar givn in th following tal N. f E fu N. f u b S f Wk f S f Wk f (a) (b) (c) (d) andthelowestenergyare thedegeneratepairs, 2 2 and2orbitalissufficientlylargetocausepairinginsomecases. 1 8 8 9 (a) (b) (c) (I) (II) (III) (IV) (V)
