1 Geometric Isomerism • cis => 2 adjacent ligands • trans => 2 ligands across the center of coordination sphere [PtCl 2 (NH 3 ) 2 ] Geometric Isomerism • fac (facial) => three identical ligands occupying the corners of a common triangular surface • mer (meridional) => three identical ligands occupying three consecutive corners of a square plane Cl Cl Cl Cl CL CL fac mer Enantiomers of O h complexes View down 3-fold axis Chelating ligands define left or right hand Helix rotation Lower case letters are used for mirror image Structures δ λ δ λ D 4h has inversion: This causes loss of chirality d-orbitals
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Geometric Isomerism
• cis => 2 adjacent ligands• trans => 2 ligands across the center of
coordination sphere
[PtCl2(NH3)2]
Geometric Isomerism• fac (facial) => three identical ligands
occupying the corners of a common triangular surface
• mer (meridional) => three identical ligands occupying three consecutive corners of a square plane
Cl
Cl
Cl
Cl
CL
CL
fac mer
Enantiomers of Oh complexesView down 3-fold axisChelating ligands define left or right handHelix rotation
Lower case letters are used for mirror imageStructures
δ λ
δ λ
D4h has inversion:This causes loss ofchirality
d-orbitals
2
a1g Molecular Orbitals
t1g Molecular Orbitalseg Molecular Orbitals
Octahedral Field Splitting Pattern Splitting ofd-Orbitals in Oh Field
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Reducing axial ligand repulsions splitsThe degenerate eg and t2g orbitals
Jahn-Teller distortion
Octahedral MO
Diagram
Electronic Spectrum of [Ti(H2O)6]+3
t12g e0
g is ground state
1300 243 oKJcmmol
− = ≈ ∆
1max 20,300 243 o
KJcmmol
λ −= = ≈ ∆
Spectral Effects of Ligands and Metals
• Different binding atoms of ligands exert different repulsions on the metal orbitals
• Different oxidation states of the metal-increases with increasing oxidation number
• There is no quantified measure of energy changes as a result of these factors from crystal field theory
o∆
Spectral characteristics of octahedral Co complexes
= transition probability (extinction coefficient)ε
o∆ Determines the color of complexes: t2g – eg
The energy of the wavelength corresponding tois
o∆
E hν=
4
Variation of ∆o
Metal ions of equal oxidation stateare placed in a spectrochemicalSeries:Mn(II)<Ni(II)<Co(II) <Fe(III)<Cr(III)<Co(III)<Ru(III)<Mo(III)<Rh(III)<Pd(III)<Ir(III)<Pt(IV)
Weak vs. Strong Field Splitting
Crystal Field Splitting Diagrams
Low spin High spin
Tetrahedral ML4
Tetrahedral ligandsImpinge upon the dOrbitals to a smallerDegree than Oh geometry
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Relationship of ∆t and ∆o
Relationship of Octahedral vs Square Planar Geometry
π-Orbitals in L-M-LOctahedral MO Diagram, with π-Bonding
Octahedral MO Diagram, with π-Bonding Pi bonding explains field strength of ligands
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Pi interactions are important in organo-metallic reactions
Pi backbonding: metalActs as Lewis base andProvides electron densityTo empty pi* orbitals ofligand
Microstate Term SymbolsLigand Field Theory
Mulliken symbols fromIrreducible tables
Donation ofe- density
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Atomic termSymbolLS coupling
Symmetry label hasSame multiplicity asParent term symbol.T2g and E2g derive fromD term symbol: assymetricDegenerate population
Irreducible has same symmetryAs term symbol: excited statesWith same multiplicity are More probable
F: A2g + T1g + T2gP: T1g
t2g2
t2g1eg
1
e22
LS coupling overcomeBy ligand strength
B: Racah parameter-amount of repulsion between terms of samemultiplicity
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Forbidden transitions are very weak (of low probability)
Transition metal complexes have color as a result of vibronicdistortions away from symmetry
High and low spin complexes have unique propertiesincluding magnetic field interactions, ligand association, and Spectral differences.