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Coordination Chemistry Electronic Spectra of Metal Complexes

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Presentation on theme: "Coordination Chemistry Electronic Spectra of Metal Complexes"— Presentation transcript:

1 Coordination Chemistry Electronic Spectra of Metal Complexes

2 Electronic spectra (UV-vis spectroscopy)

3 Electronic spectra (UV-vis spectroscopy)
hn DE

4 The colors of metal complexes

5

6 Electronic configurations of multi-electron atoms
What is a 2p2 configuration? n = 2; l = 1; ml = -1, 0, +1; ms = ± 1/2 Many configurations fit that description These configurations are called microstates and they have different energies because of inter-electronic repulsions

7 Electronic configurations of multi-electron atoms
Russell-Saunders (or LS) coupling For the multi-electron atom L = total orbital angular momentum quantum number S = total spin angular momentum quantum number Spin multiplicity = 2S+1 ML = ∑ml (-L,…0,…+L) MS = ∑ms (S, S-1, …,0,…-S) For each 2p electron n = 1; l = 1 ml = -1, 0, +1 ms = ± 1/2 ML/MS define microstates and L/S define states (collections of microstates) Groups of microstates with the same energy are called terms

8 Determining the microstates for p2

9 Spin multiplicity 2S + 1

10 Determining the values of L, ML, S, Ms for different terms
2P

11 One remaining microstate
Classifying the microstates for p2 Largest ML is +2, so L = 2 (a D term) and MS = 0 for ML = +2, 2S +1 = 1 (S = 0) 1D One remaining microstate ML is 0, L = 0 (an S term) and MS = 0 for ML = 0, 2S +1 = 1 1S Next largest ML is +1, so L = 1 (a P term) and MS = 0, ±1/2 for ML = +1, 2S +1 = 3 3P Spin multiplicity = # columns of microstates

12 Next largest ML is +1, so L = 1 (a P term) and MS = 0, ±1/2 for ML = +1, 2S +1 = 3 3P Largest ML is +2, so L = 2 (a D term) and MS = 0 for ML = +2, 2S +1 = 1 (S = 0) 1D ML is 0, L = 0 2S +1 = 1 1S

13 Energy of terms (Hund’s rules)
Lowest energy (ground term) Highest spin multiplicity 3P term for p2 case 3P has S = 1, L = 1 If two states have the same maximum spin multiplicity Ground term is that of highest L

14 Determining the microstates for s1p1

15 Determining the terms for s1p1
Ground-state term

16 Coordination Chemistry Electronic Spectra of Metal Complexes cont.

17 Electronic configurations of multi-electron atoms
Russell-Saunders (or LS) coupling For the multi-electron atom L = total orbital angular momentum quantum number S = total spin angular momentum quantum number Spin multiplicity = 2S+1 ML = ∑ml (-L,…0,…+L) MS = ∑ms (S, S-1, …,0,…-S) For each 2p electron n = 1; l = 1 ml = -1, 0, +1 ms = ± 1/2 ML/MS define microstates and L/S define states (collections of microstates) Groups of microstates with the same energy are called terms

18 before we did: p2 ML & MS Microstate Table States (S, P, D)
Spin multiplicity Terms 3P, 1D, 1S Ground state term 3P

19 For metal complexes we need to consider
d1-d10 d2 3F, 3P, 1G, 1D, 1S For 3 or more electrons, this is a long tedious process But luckily this has been tabulated before…

20 Transitions between electronic terms will give rise to spectra

21 Selection rules (determine intensities)
Laporte rule g  g forbidden (that is, d-d forbidden) but g  u allowed (that is, d-p allowed) Spin rule Transitions between states of different multiplicities forbidden Transitions between states of same multiplicities allowed These rules are relaxed by molecular vibrations, and spin-orbit coupling

22 Group theory analysis of term splitting

23 High Spin Ground States
An e electron superimposed on a spherical distribution energies reversed because tetrahedral High Spin Ground States dn Free ion GS Oct. complex Tet complex d0 1S t2g0eg0 e0t20 d1 2D t2g1eg0 e1t20 d2 3F t2g2eg0 e2t20 d3 4F t2g3eg0 e2t21 d4 5D t2g3eg1 e2t22 d5 6S t2g3eg2 e2t23 d6 t2g4eg2 e3t23 d7 t2g5eg2 e4t23 d8 t2g6eg2 e4t24 d9 t2g6eg3 e4t25 d10 t2g6eg4 e4t26 Holes in d5 and d10, reversing energies relative to d1 A t2 hole in d5, reversed energies, reversed again relative to octahedral since tet. Holes: dn = d10-n and neglecting spin dn = d5+n; same splitting but reversed energies because positive. Expect oct d1 and d6 to behave same as tet d4 and d9 Expect oct d4 and d9 (holes), tet d1 and d6 to be reverse of oct d1

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

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

26 d2 3F, 3P, 1G, 1D, 1S Real complexes

27 Tanabe-Sugano diagrams

28 Electronic transitions and spectra

29 Other configurations d3 d1 d9 d2 d8

30 Other configurations d3 The limit between high spin and low spin

31 Determining Do from spectra
One transition allowed of energy Do

32 Determining Do from spectra
mixing Lowest energy transition = Do

33 E (T1gA2g) - E (T1gT2g) = Do
Ground state mixing E (T1gA2g) - E (T1gT2g) = Do

34 The d5 case All possible transitions forbidden
Very weak signals, faint color

35 Some examples of spectra

36 Charge transfer spectra
Metal character LMCT Ligand character Ligand character MLCT Metal character Much more intense bands

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