1) The document discusses Tanabe-Sugano diagrams which are commonly used to interpret spectra of transition metal complexes including both weak and strong ligand fields.
2) Key differences between Orgel and Tanabe-Sugano diagrams are that the latter includes low spin states, plots energies relative to the ground state, and uses Δo/B on the x-axis rather than just ligand field splitting.
3) An example of using a Tanabe-Sugano diagram to analyze spectra from a [V(H2O)6]3+ complex is shown, identifying transitions between the 3T1g and 3T2g states.
1) The document discusses Tanabe-Sugano diagrams which are commonly used to interpret spectra of transition metal complexes including both weak and strong ligand fields.
2) Key differences between Orgel and Tanabe-Sugano diagrams are that the latter includes low spin states, plots energies relative to the ground state, and uses Δo/B on the x-axis rather than just ligand field splitting.
3) An example of using a Tanabe-Sugano diagram to analyze spectra from a [V(H2O)6]3+ complex is shown, identifying transitions between the 3T1g and 3T2g states.
1) The document discusses Tanabe-Sugano diagrams which are commonly used to interpret spectra of transition metal complexes including both weak and strong ligand fields.
2) Key differences between Orgel and Tanabe-Sugano diagrams are that the latter includes low spin states, plots energies relative to the ground state, and uses Δo/B on the x-axis rather than just ligand field splitting.
3) An example of using a Tanabe-Sugano diagram to analyze spectra from a [V(H2O)6]3+ complex is shown, identifying transitions between the 3T1g and 3T2g states.
1) The document discusses Tanabe-Sugano diagrams which are commonly used to interpret spectra of transition metal complexes including both weak and strong ligand fields.
2) Key differences between Orgel and Tanabe-Sugano diagrams are that the latter includes low spin states, plots energies relative to the ground state, and uses Δo/B on the x-axis rather than just ligand field splitting.
3) An example of using a Tanabe-Sugano diagram to analyze spectra from a [V(H2O)6]3+ complex is shown, identifying transitions between the 3T1g and 3T2g states.
Course Code: 201-B Dr. Sriparna Dutta Inorganic Group III and IV
REFERENCE BOOKS: 1. Electronic Spectra of Transition Metal Complexes by D. Sutton 2. Introduction to Ligand Field Theory: Figgis 3. Concise Inorganic Chemistry by J. D. Lee Tanabe Sugano Diagram Though it is possible to add low-spin states to an Orgel Diagram, Tanabe Sugano diagrams are commonly used instead for interpretation of spectra including both weak and strong fields.
Tanabe Sugano diagrams are similar to Orgel diagrams in that they show how energy levels change with Δo, but they differ in several ways:
• Ground State is taken as the abscissa and provides a constant reference point. The other energy states are plotted relative to this. 1.
• Low spin terms i.e. states where the spin multiplicity is lower than ground state are included. 2.
• In order to make the diagrams general for different metal ions with same electronic configuration and to allow for different ligands energy/B is plotted against Δo/B 3. Difference between Orgel and Tanabe-Sugano Diagrams
Sl. No ORGEL TANABE-SUGANO
1 Weak Field Weak-Strong Field
2 Spin Allowed Spin allowed and forbidden
3 E v/s CFS E/B vs Δo/B
Tanabe Sugano Diagram for d2 system [V(H2O)6]3+ Green and 2 bands: 17100 cm-1 and 25200 cm-1
d2 configuration: 3F, 3P, 1D, 1G, 1S
A2g Possible Arrangements are:
3F T2g (F) dxy1 dyz1 dxzo T1g (F) dxy1 dyz0 dxz1 T1g (F) 3P T1g (P) dxy0 dyz1 dxz1 When one electron gets promoted:
dxy1 dz21 T2g (F) dyz1 dx2-y21 dzx1 dx2-y21
dxy1 dx2-y21 T1g (P) dyz1 dz21 dzx1 dz21
When both electrons get promoted:
dx2-y21 dz21 A2g (F) Lower energy band is assigned to transition: 3T (F) 3T (F) 1g 2g Then a rough estimate of position of 3T (F) 3A (F) can be made because in strong 1g 2g field limit, these transitions are (t2g)1(eg)1 (t2g)2 (E= Δo ) and (eg)2 (t2g)2 (E= 2Δo )
So, if electron gets excited from
T1g (F) A2g (=2 x Δo) ( =34200 cm-1) But second absorption is 25, 200 cm-1 which is much less than 34, 200 cm-1. 1A 1g 3A2g (F)
1E 1T 1S g 2g (G) 1T E/B 1g 3T1g (P) 3T2g (F) υ2 1G 1A1g (G) 38.6
Ratio υ2 = 25200 = 1.47 For First Transition: υ1 17100 E/B=25.8 For second transition: E/B=38.6 υ2/υ1 E[3T2g(F)]= 25.8 x B = 25.8 x 860 2 = 22188 cm-1 1
10 20 30 E[T1g(P)]= 38.6 x 860
Δo/B = 33196 cm-1 27.5
These values of υ1 and υ2 are higher as B we are using for free V3+ Now to see how much υ1 and υ2 are varying First Band= Ecalculated/ E Observed = 22188/17100 = 1.3 Second Band= 33200/25200 =1.3 We have accounted for 1.3 times higher B. B’= B/1.3 =860/3= 662 cm-1 Δo/B’= 27.5 Δo = 27.5 x B’ =27.5 x 662 = 18192 cm-1 β = B’/ B = 662/860 = 0.77 d3 configuration υ = 17400 cm-1, υ = 24600 cm-1, υ = 37800 cm-1 1 2 3 Find Δo, B’ and β (B for Cr3+ = 918 cm-1) •Ratio of energies of the first two excited states 4t2g(F) and 4T1g(F) above the gr0und state 4A2g(F) is plotted against Δo/B
• Three main d-d bands located (with assignments) at:
The ratio of two energy bands A and B is 1.42. This ratio fits with Δo/B=25.0. From figure, this corresponds to: E (4T2g(F))= 25.0 B’…………………….(1) E (4T1g(F))= 35.5 B’…………………….(2) E (4T1g(P))= 55.5 B’…………………….(3) E (4T2g(F))= 25.0 x 918 = 22950 cm-1 Δo/B’ = 25.0 E(4T1g(F))= 35.5 x 918 Δo = 25.0 x 706 =32589 cm-1 = 17653 cm-1 υ1= Ecalculated/Eobserved = 22950/ 17400 = 1.3189 υ2= Ecalculated/Eobserved β= B’/B = 32589/24600 = 706/918 = 1.3247 = 0.7690
B’=B/1.3 =918/1.3 = 706 cm-1 υ1= 16500 cm-1 υ2= 24950 cm-1 υ1= 13000 cm-1 Strong Field Weak Field
d6 configuration 5D: Ground state 1I, 1F……: Excited states
5D 5T , 5E 2g g 1I 1A , 1T , 1T , 1E , 1A 1g 1g 2g g 2g 1F 1A , 1T , 1T 2g 2g 1g The state of highest multiplicity for d6 is 5D and for weak field, there is only 1 spin allowed transition: 5T 5E 2g g
Low spin d6 complexes possess the
orbital singlet ground state 1A1g arising from strong field configuration (t2g)6 At certain point 5T2g goes higher and 1A becomes ground state term. 1g υ2 • Discontinuity is TS diagram indicates that electron starts pairing υ1 d6 d6
Strong Field Weak Field S=0 (same as d1) Singly degenerate Here G.S term is A1g
