1 Electronic (UV-visible) Spectroscopy ｜ Electronic ｜ XPS UPS UV-visible

2 UV-visible spectroscopy ligand  * (1) metal-metal (d-d) transition  * metal-ligand metal d (2) charge transfer (MLCT) ligand-metaln (LMCT)metal d n (3) ligand-centered transition ligand   instrument sample energy energy energy output source selector analyzer computer electric connection light path absorbance Io A = log ―― =  cl I  : extinction coefficient c: concentration mol/L (M) l: path length (cm)

3 selection rules 1.only one electron is involved in any transition 2.there must be no net change of spin  S = 0 3.it must involve an overall change in orbital angular momentum of one unit  L = ±1 4.Laporte (or parity) selection rule only g →u and u →g transitions are allowed vibronic coupling – interaction between electronic and vibrational modes electronic transition  Laporte allowed (charge transfer) (1000—50000) Laporte forbidden (d-d transition) spin allowed; noncentrosymmetiric 100—200 (200—250) spin allowed; centrosymmetric5—100 (20—100) spin forbidden0.01—1 (< 1)

4 [Co(H 2 O) 6 ] 2+ [CoCl 4 ] 2- [Mn(H 2 O) 6 ] 2+

5 d-d transition crystal field splitting  o size and charge of the metal ion and ligands 4d metal ~50% larger than 3d metal 5d metal ~25% larger than 4d metal 5d > 4d > 3d crystal field stabilization energy (CFSE) spin-pairing energy high-spin/low spin configuration d 4 ~ d 7 d 4

6 other shapes tetrahedral  t = 4/9  o tetrahedron octahedron elongated square octahedron planar

7 d 1 [Ti(H 2 O) 6 ] 3+ hole formalism d 2 possible electron possible arrangements of electronstransitions h  o

8 Russell-Saunders term symbols for free atoms and ions S: total spin quantum number  m s L: total orbital angular quantum number  m l L = 0, 1, 2, 3, 4, ………….. S P D F G J: total angular quantum number L+S, ……, │ L-S │ d 2 configuration 10! ———— = 45 microstates 8! 2! S L 4( ) 3( )( ) ( )( ) ( ) 2( )( ) ( )( ) ( )( ) ( )( ) 1( )( ) ( )( ) ( ) 0( )( ) ( )( ) ( )( ) ( )( ) 1 G 3 F 1 D 3 P 1 S = 45 ground term 2S+1 L J

9 splitting of terms in various chemical environments d orbitals in O h environment consider pure rotational O subgroup rotation by angle  ==> R(r),  (  ), ψ s invariant only  (  ) will be altered  (  ) = e im  ==>  (  ) = e im(  +  ) m = 2, 1, 0, -1, -2 e 2i  e 2i  +  ) e i  e i  +  ) e 0 ======>e 0 e -i  e -i  +  ) e -2i  e -2i  +  ) states for d n systems in Russell-Saunders coupling

10 transformation matrix e 2i  e i  e e -i  e -2i  sum of the diagonal elements sin(l + 1/2)   (  ) = ——————— sin(  /2) for d orbitals sin(5  /2)  (  ) = 5  (C 2 ) = ————— = 1 sin(  /2) sin(5  /3) sin(5  /4)  (C 3 ) = ————— = -1  (C 4 ) = ————— = -1 sin(  /3) sin(  /4) ==>  = e g + t 2g

11 splitting of one-electron levels in an O h environment splitting of one-electron levels in various symmetries

12 determine the spin multiplicity of each term d 2 configuration in O h environment (i)t 2g 2 a A 1g + b E g + c T 1g + d T 2g total degeneracy 15 abcd I1113 II1131 III3311 (ii)t 2g 1 e g 1 a T 1g + b T 2g total degeneracy 24 only possibility 1 T 1g 1 T 2g 3 T 1g 3 T 2g (iii) e g 2 a A 1g + b A 2g + c E g total degeneracy 6 abc I131 II S 1 A 1g 1 G 1 A 1g 1 E g 1 T 1g 1 T 2g 3 P 3 T 1g 1 D 1 E g 1 T 2g 3 F 3 A 1g 3 T 1g 3 T 2g

13 method of descending symmetry consider d 2 ion in O h environment from correlation table for group O h (i) t 2g 2 A 1g E g T 1g T 2g lowering the symmetry to C 2h t 2g a g + a g + b g t 2g × t 2g = 1 A 1g 1 E g 3 T 1g 1 T 2g possible spin multiplicity ˇ corresponding 1 A g 1 A g 3 A g 1 A g representations 1 B g 3 B g 1 A g in C 2h 3 B g 1 B g a g × a g A g ====> 1 A g a g × a g ’ A g ====> 1 A g 3 A g a g × b g B g ====> 1 B g 3 B g a g ’ × a g ’ A g ====> 1 A g a g ’ × b g B g ====> 1 B g 3 B g b g × b g A g ====> 1 A g ===> total 4 1 A g + 3 A g B g B g

14 (ii) e g 2 A 1g A 2g E g lowering the symmetry to D 4h e g a 1g + b 1g a 1g 2 A 1g possible spin multiplicity 1 A 1g a 1g b 1g B 1g possible spin multiplicity 1 B 1g 3 B 1g b 1g 2 A 1g possible spin multiplicity 1 A 1g ==>D 4h O h 1 A 1g 3 B 2g 3 A 1g 1 A 1g 1 B 1g 1 E g (iii) t 2g 1 e g 1 ???? consider d 2 ion in T d environment from splitting of energy level in T d symmetry 3 F 3 A 2 3 T 1 3 T 2 1 D 1 E 1 T 2 3 P 3 T 1 1 G 1 A 1 1 E 1 T 1 1 T 2 1 S 1 A 1 electron configurations e 2 A 1 A 2 Etotal degeneracy 6 et 2 T 1 T 2 total degeneracy 24 t 2 2 A 1 E T 1 T 2 total degeneracy 15 assign the correct spin multiplicity ???

15 splitting of the terms for d 2 ion in several point groups

16 correlation diagram for a d 2 ion in O h environment

17 correlation diagram for a d 2 ion in T d environment

18 Orgel diagrams d 1, d 6 /d 4, d 9  = 10 D q E T 2 T 2g E g E g T 2 g T 2 E d 1, d 6 tetrahedral d 1, d 6 octahedral d 4, d 9 octahedral d 4, d 9 tetrahedral

19 d 2, d 7 /d 3, d 8 A 2 →T 2  1 = 10D q T 1 →T 2  1 = 8D q + c A 2 →T 1 (F)  2 = 18D q - cT 1 (F)→T 1 (P)  2 = 18D q + c A 2 →T 1 (P)  1 = 15B + 12D q + cT 1 →A 2  3 = 15B + 6D q + 2c d 2, d 7 tetrahedral D q d 2, d 7 octahedral d 3, d 8 octahedral d 3, d 8 tetrahedral cm-1

20

21 Tanabe-Sugano diagrams

22

23 simplified Tanabe-Sugano diagrams d2d2 d3d3 d4d4 d5d5 d6d6 d7d7 d8d8

24 magnitude of  o Mn(II) < Ni(II) <Co(II) < Fe(II) < V(II) < Fe(III) < Cr(III) < V(III) < Co(III) < Mn(IV) < Mo(III) < Rh(III) < Pd(IV) < Ir(III) < Re(IV) < Pt(IV)  o values for octahedral [M(H 2 O) 6 ] n+ complexes  o (cm -1 ) Ti Mn Co V Mn Co Cr Fe Ni Cr Fe Cu spectrochemical series I - < Br - < -SCN - < Cl - < F - < urea < OH - < CH 3 COO - < C 2 O 4 - < H 2 O < -NCS - < glycine < pyridine ~ NH 3 < en < SO 3 2- < o-phenanthroline < NO 2 - < CN - < PR 3 < CO ex. [Co(H 2 O) 6 ] 3+  o = cm -1 [Co(NH 3 ) 6 ] 3+  o = cm -1 [Co(H 2 O) 3 (NH 3 ) 3 ] 3+  o = ? 3/6 × /6 × = cm -1

25 Jørgensen prediction of 10D q and B 10D q = f · g (cm -1 × ) B = B o (1 － h · k) B o : free ion interelectronic repulsion parameter Jahn-Teller distortions distortion will occur whenever the resulting splitting energy levels yields additional stabilization __ d x 2 -y 2 __ d z 2 e g __ __ __ d z 2 __ d x 2 -y 2 or __ d xy __ __d xz, d yz t 2g __ __ __ __ __ d xz, d yz __ d xy

26 [M(H 2 O) 6 ] n+ Ti 3+ (d 1 ) V 3+ (d 2 ) Cr 3+ (d 3 ) Mn 2+ (d 5 ) Fe 2+ (d 6 ) Co 2+ (d 7 ) Ni 2+ (d 8 ) Cu 2+ (d 9 ) Cr 2+ (d 4 )

27 d 1 d 2

28 d3d3

29 d3d3

30 d4d5d4d5

31 d6d6

32 d6d6

33 d6d6

34 d7d7

35 d 8 d 9