Presentation on theme: "Five Slides About: UV-Vis Spectroscopy and Tanabe-Sugano Diagrams Sabrina G. Sobel Hofstra University Created by Sabrina.G.Sobel,"— Presentation transcript:
Five Slides About: UV-Vis Spectroscopy and Tanabe-Sugano Diagrams Sabrina G. Sobel Hofstra University Created by Sabrina.G.Sobel, Hofstra University and posted on VIPEr (www.ionicviper.org) on March 8, Copyright Sabrina G. Sobel This work is licensed under the Creative Commons Attribution-NonCommerical-ShareAlike 3.0 Unported License. To view a copy of this license visit
d-Orbital Splitting in Transition Metal Complexes Octahedral (O h ) symmetry: d-orbitals split into t 2g and e g sets o is the splitting energy, and is dictated by ligand field strength (see spectrochemical series) Tetrahedral (T d ) symmetry: d-orbitals split into e and t 2 sets T is always smaller than o since total ligand field strength is less e g t 2g t2et2e oo CN -, CO > NO 2 -, phen > bpy > SO 3 2- > NH 3 > NCS - > H 2 O > OH - > F - > Cl - > SCN - > Br - > I - Spectrochemical Series
UV-Vis Spectroscopy of Transition Metal Complexes Symmetry Rules: – LaPorte: allowed transitions occur between orbitals of opposite symmetry WRT inversion (gerade (even) and ungerade (odd) in character tables) – Spin Multiplicity: allowed transition occur when spin multiplicity is unchanged d 0 metal cations: charge-transfer transitions – LaPorte allowed; ligand * to metal d orbital d 1 to d 9 metal cations: d d transitions – LaPorte forbidden; same orbital type d 10 metal cations: no d d transitions because the orbitals are filled
d d Transitions and Color TM complex (d 1 to d 9 ) absorbs visible light Transmitted light is opposite color to absorbed light Energy of absorbed light is proportional to Strong field ligand: low nm Weak field ligand: high nm Example: Fe(phen) 3 2+ – max = 508 nm (green) – Transmitted color: red- orange
d d Transitions and Color Complexes are arranged in order of decreasing oct Color transmitted increases in energy from yellow olive Cobalt complexes with: (a) CN –, (b) NO 2 –, (c) phen, (d) EN, (e) NH 3, (f) gly, (g) H 2 O, (h) oxalate 2–, (i) CO 3 2–.
Russell-Saunders Coupling Review: Determining ground state of Transition Metal cations 1.Draw d-orbitals and fill with # electrons for desired ion 2.Calculate Spin Multiplicity = #unpaired electrons +1 = S 3.Find maximum M L (m l = -2, -1, 0, 1, 2 for d orbitals) = L 4.Ground state term: S L = (step 2) (Step 3) Example: Cr(II); d 4 1.Orbital diagram = (-1) = 2 D 4. 5 D is the ground state term Spin-allowed transitions will be pentet to pentet L :
Symmetry lowering from spherical to octahedral electrical field is applied to ground state and excited state terms Relative energies of states are plotted against ligand field strength TermDegeneracyStates in an octahedral field S1A 1g P3T 1g D5E g + T 2g F7A 2g + T 1g + T 2g G9A 1g + E g + T 1g + T 2g H11E g + T 1g + T 1g + T 2g I13A 1g + A 2g + E g + T 1g + T 2g + T 2g O h Tanabe-Sugano Diagrams O h T-S Diagram for a d 4 ion d 4 ion g.s.
B = Racah Parameter; takes into account electron repulsion energy X-axis: /B Y-axis: E/B High spin vs. low spin 5 D 3 G Spin allowed transitions: – 5 E to 5 T 2 (UV-Vis range) – 3 T 1 to 3 E (large energy gap!) O h Tanabe-Sugano Diagrams O h T-S Diagram for a d 4 ion e g t 2g [Cr(CH 3 CO 2 ) 2 (H 2 O)] 2 is brick red; CrCl 2 (H 2 O) 4 is green
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