Advanced Inorganic Chemistry

CHMI 3317 EL

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Classes of coordination compounds

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The d orbitals

d orbital splitting(octahedral environment)

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Metal atomic orbitals(AOs) and ligand grouporbitals (LGOs) involvedin forming the MOs ofan octahedral complex

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Metal atomic orbitals (AOs) and ligand group orbitals (LGOs) involved informing the MOs of an octahedral complex

Molecular orbital diagram (Oh)σ bonding only

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Another simplified depiction of an MO diagram for an octahedral complex

Here: The antibonding orbitals are identified by an asterisk.

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π-Bonding

π-Acceptor π-Donor

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Metal carbonyls

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Structures of binary metal carbonyls

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Structures of binary metal carbonyls

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Preparation ofcarbonyl compounds

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Why are most carbonyls in the centre of this table?

Electron counting with tetranuclear osmium carbonyls

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CO as a ligand

MO diagram Contour lines

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Dependence of bond order and stretching frequencies on orbital interactions

Carbonyl stretching frequencies

d(C-O)/pm ν CO (cm-1)

CO (free) 113 2143 CO bond order = 3

CO* (singlet excited state) 124 1489 2p strongly antibonding

M-CO(e.g. Cr(CO)6)

~ 115 1850-2120(2000)

CO bond order = 2-3

M2-µ2-CO 1750-1850

M3-µ3-CO 1620-1730

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CO stretching frequencies

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The number of IR bands depends on molecular symmetry

L ν CO (cm-1)PF3 2055, 2090PCl3 1991, 2040P(OMe)3 1888, 1977PPh3 1835, 1934pyridine 1746, 1888

Carbonyl stretching frequenciesfor fac-L3Mo(CO)3

NO > CO > RNC > PF3 > PCl3 > PCl2R > P(OR)3 > PR3 > RCN > NH3

Order of π-acceptor strength

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Complex ν CO (cm-1)[Ti(CO)6]2- 1748[V(CO)6]- 1859[Cr(CO)6] 2000[Mn(CO)6]+ 2100[Fe(CO)6]2+ 2204free CO 2143

Dependence of stretching frequencieson complex charge

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Terminal and bridging NO in complexes

(a) [Ir(PPh3)2(CO)(NO)Cl]+

(b) [Ru(PPh3)2(NO)2Cl]+

Structures of some NO complexes

Complexes containing bent NO ligands

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Stereochemical control of valence: [Co(diars)2(NO)]2+

diars