Transition Metals, Compounds and Complexes or

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Presentation transcript:

Transition Metals, Compounds and Complexes or Electronic Spectroscopy of Transition Metal Complexes Dr. E.R. Schofield Lecture 3: Interpretation of weak field spectra Electronic spectra from Orgel diagrams Orgel diagram for d2, d3, d7, d8 ions

d1  d6 d4  d9 Orgel diagram for d1, d4, d6, d9 Energy T2 E d1, d6 tetrahedral Eg T2g d1, d6 octahedral d4, d9 tetrahedral or T2 or E T2g or Eg or d4, d9 octahedral D D D ligand field strength

[Ti(OH2)6]3+ d1 oct 2Eg 2Eg  2T2g 2D 2T2g - D A E LF strength n / cm-1 - 30 000 20 000 10 000 2Eg 2Eg  2T2g 2D 2T2g E LF strength Orgel diagram for d1, d4, d6, d9 D d4, d9 tetrahedral T2g or T2 d4, d9 octahedral Eg or E d1, d6 tetrahedral d1, d6 octahedral

? P T2(g) and E(g) D F Effect of a ligand field on Ground State Terms GS d1 d9 2D d2 d8 3F 3P d3 d7 4F 4P d4 d6 5D d5 6S free ion ligand field D T2(g) and E(g) P F ?

Octahedral d2 complex d2  d7 3P: high repulsion In a LF, these orbitals are unaffected xz + z2 yz + z2 xy + x2-y2 3T1g 3F: low repulsion In a LF, orbitals in the t2g set go down in energy, orbitals in the eg set go up in energy 3A2g eg eg singly degenerate, high energy x2-y2 + z2 x2-y2 + yz x2-y2 + xz xy + z2 xy + xz xy + yz xz + yz 3T2g eg t2g triply degenerate, medium energy 3T1g t2g t2g triply degenerate, low energy

Octahedral d3 complex (same terms, different spin) d3  d8 4P: high repulsion In a LF, these orbitals are unaffected  4T1g 4F: low repulsion The order of energy levels is the opposite to that for a d2 ion  4T1g 4T2g 4A2g

Ligand field strength (Dq) Orgel diagram for d2, d3, d7, d8 ions Quantum Mixing Energy A2 or A2g T1 or T1g T2 or T2g T1 or T1g P F d2, d7 tetrahedral d2, d7 octahedral d3, d8 octahedral d3, d8 tetrahedral Ligand field strength (Dq)

Energy level diagram for oct d2, d7, tet d3, d8 15 B' 15 B 15 B > 15 B' 10 Dq 6 Dq 2 Dq T1(g) A2(g) T2(g) x A2(g) T2(g) T1(g) P F 10 Dq 6 Dq 2 Dq

Calculating B' and x d7 octahedral complex n1 n2 n3 n1 n2 n3 [Co(H2O)6]2+ n1 n2 n3 4T1g n1 n2 n3 n1 = 8 000 cm-1 n2 = 16 000 cm-1 n3 = 19 400 cm-1 A 10 Dq 6 Dq 2 Dq x 15 B' 4A2g v / cm-1 25 000 20 000 15 000 10 000 4T2g 4T1g

Ligand field strength (Dq) Orgel diagram for d2, d3, d7, d8 ions Energy A2 or A2g T1 or T1g T2 or T2g T1 or T1g P F d2, d7 tetrahedral d2, d7 octahedral d3, d8 octahedral d3, d8 tetrahedral Ligand field strength (Dq)

Energy level diagram for oct d2, d7, tet d3, d8 n1: x + 8 Dq n2: 2 x + 6 Dq + 15 B' n3: x + 18 Dq A2(g) n1 n2 n3 n1: T2(g)  T1(g) n2: T1(g)(P)  T1(g) n3: A2(g)  T1(g) T1(g) 10 Dq x P 15 B 15 B' T2(g) 2 Dq F 6 Dq T1(g) x