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Electronic (UV-visible) Spectroscopy

Electronic (UV-visible) Spectroscopy

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Electronic (UV-visible) Spectroscopy

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

  2. UV-visible spectroscopy ligand p* (1) metal-metal (d-d) transition s* metal-ligand metal d (2) charge transfer (MLCT) ligand-metaln (LMCT) metal d n (3) ligand-centered transition ligand p s instrumentsample energy energy energy output source selector analyzer computer electric connection light path absorbanceIo A = log ―― = ecl I e: 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 DS = 0 3. it must involve an overall change in orbital angular momentum of one unit DL = ±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 e Laporte allowed (charge transfer) 10000 (1000—50000) Laporte forbidden (d-d transition) spin allowed; noncentrosymmetiric 100—200 (200—250) spin allowed; centrosymmetric 5—100 (20—100) spin forbidden 0.01—1 (< 1)

  4. [Co(H2O)6]2+ [CoCl4]2- [Mn(H2O)6]2+

  5. d-d transition crystal field splitting Do 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 d4 ~ d7 d4

  6. other shapes tetrahedral Dt = 4/9 Do tetrahedron octahedron elongated square octahedron planar

  7. hu = Do d1 [Ti(H2O)6]3+ hole formalism d2 possible electron possible arrangements of electronstransitions

  8. 2S+1LJ Russell-Saunders term symbols for free atoms and ions S: total spin quantum number Sms L: total orbital angular quantum number Sml L = 0, 1, 2, 3, 4, ………….. S P D F G 1 3 5 7 9 J: total angular quantum number L+S, ……,│L-S│ d2 configuration 10! ———— = 45 microstates 8! 2! S +1 0 -1 L 4 (2+ 2-) 3 (2+ 1+) (2+ 1-) (2- 1+) (2- 1-) (1+ 1-) 2 (2+ 0+) (2+ 0-) (2- 0+) (2- 0-) (1+ 0+) (1+ 0-) (1- 0+) (1- 0-) 1 (2+ -1+) (2+ -1-) (2- -1+) (2- -1-) (0+ 0-) 0 (1+ -1+) (1+ -1-) (1- -1+) (1- -1-) (2+ -2+) (2+ -2-) (2- -2+) (2- -2-) 1G 3F1D 3P 1S 9 + 21 + 5 + 9 + 1 = 45 ground term

  9. states for dn systems in Russell-Saunders coupling splitting of terms in various chemical environments d orbitals in Oh environment   consider pure rotational O subgroup rotation by angle a ==> R(r), Q(q), ψs invariant only F(f) will be altered F(f) = eimf ==> F(f + a) = eim(f + a) m = 2, 1, 0, -1, -2 e2if e2i(f + a) eif ei(f + a) e0======>e0 e-if e-i(f + a) e-2if e-2i(f + a)

  10. transformation matrix e2ia0 0 0 0 0 eia0 0 0 0 0 e00 0 0 0 0 e-ia0 0 0 0 0 e-2ia sum of the diagonal elements sin(l + 1/2)a c (a) = ——————— sin(a/2) for d orbitals sin(5p/2) c (E) = 5 c (C2) = ————— = 1 sin(p/2) sin(5p/3) sin(5p/4) c (C3) = ————— = -1 c (C4) = ————— = -1 sin(p/3) sin(p/4) ==> G = eg + t2g

  11. splitting of one-electron levels in an Oh environment splitting of one-electron levels in various symmetries

  12. determine the spin multiplicity of each term d2 configuration in Oh environment (i) t2g2 aA1g + bEg + cT1g + dT2g total degeneracy 15 a b c d I 1 1 1 3 II 1 1 3 1 III 3 3 1 1 (ii) t2g1eg1 aT1g + bT2g total degeneracy 24 only possibility 1T1g 1T2g 3T1g 3T2g (iii) eg2 aA1g + bA2g + cEg total degeneracy 6 a b c I 1 3 1 II 3 1 1 1S 1A1g 1G 1A1g 1Eg 1T1g 1T2g 3P 3T1g 1D 1Eg 1T2g 3F 3A1g 3T1g 3T2g

  13. method of descending symmetry consider d2 ion in Oh environment from correlation table for group Oh (i) t2g2 A1g Eg T1g T2g lowering the symmetry to C2h t2g ag +ag +bg t2g × t2g = 1A1g 1Eg 3T1g 1T2g possible spin 1 1 1 3 multiplicity 1 1 3 1 ˇ 3 3 1 1 corresponding 1Ag 1Ag 3Ag1Ag representations 1Bg 3Bg1Ag in C2h3Bg1Bg ag × ag Ag ====>1Ag ag × ag’ Ag ====>1Ag 3Ag ag × bg Bg ====>1Bg 3Bg ag’ × ag’ Ag ====>1Ag ag’ × bg Bg ====>1Bg 3Bg bg × bg Ag ====>1Ag ===> total 41Ag + 3Ag + 21Bg + 23Bg

  14. (ii) eg2 A1g A2g Eg lowering the symmetry to D4h eg a1g + b1g a1g2A1g possible spin multiplicity 1A1g a1gb1g B1g possible spin multiplicity 1B1g 3B1g b1g2 A1g possible spin multiplicity 1A1g ==> D4h Oh 1A1g 1A1g 3B2g 3A1g 1A1g 1B1g 1Eg (iii) t2g1eg1???? consider d2 ion in Td environment from splitting of energy level in Td symmetry 3F 3A23T13T2 1D 1E 1T2 3P 3T1 1G 1A11E 1T11T2 1S 1A1 electron configurations e2 A1 A2 E total degeneracy 6 et2 T1 T2 total degeneracy 24 t22 A1 E T1 T2 total degeneracy 15 assign the correct spin multiplicity ???

  15. splitting of the terms for d2 ion in several point groups

  16. correlation diagram for a d2 ion in Oh environment

  17. correlation diagram for a d2 ion in Td environment

  18. Orgel diagrams d1, d6/d4, d9 u = 10 Dq E T2 T2g Eg E g T2 g T2 E d1, d6 tetrahedral d1, d6 octahedral d4, d9 octahedral d4, d9 tetrahedral

  19. d2, d7/d3, d8 A2→T2 u1 = 10Dq T1→T2u1 = 8Dq + c A2→T1(F) u2 = 18Dq - cT1(F)→T1(P) u2 = 18Dq + c A2→T1(P) u1 = 15B + 12Dq + cT1→A2u3 = 15B + 6Dq + 2c cm-1 d2, d7 tetrahedral Dq d2, d7 octahedral d3, d8 octahedral d3, d8 tetrahedral

  20. Tanabe-Sugano diagrams

  21. d2 d3 d4 simplified Tanabe-Sugano diagrams d5 d6 d7 d8

  22. magnitude of Do 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) Do values for octahedral [M(H2O)6]n+ complexes Do (cm-1) Ti3+ 20400 Mn3+ 21000 Co3+ 19000 V3+ 19000 Mn2+ 7500 Co2+ 9750 Cr3+ 17700 Fe3+ 21000 Ni2+ 8500 Cr2+ 12500 Fe2+ 10500 Cu2+ 12600 spectrochemical series I- < Br- < -SCN- < Cl- < F- < urea < OH- < CH3COO- < C2O4- < H2O < -NCS- < glycine < pyridine ~ NH3 < en < SO32- < o-phenanthroline < NO2- < CN- < PR3 < CO ex. [Co(H2O)6]3+Do = 19000 cm-1 [Co(NH3)6]3+Do = 22900 cm-1 [Co(H2O)3(NH3)3]3+Do = ? 3/6 × 19000 + 3/6 × 22900 = 20950 cm-1

  23. Jørgensen prediction of 10Dq and B 10Dq = f · g (cm-1 × 10-3) B = Bo (1 - h · k) Bo : free ion interelectronic repulsion parameter Jahn-Teller distortions distortion will occur whenever the resulting splitting energy levels yields additional stabilization __ dx2-y2 __ dz2 eg__ __ __ dz2 __ dx2-y2   or __ dxy __ __dxz, dyz t2g __ __ __ __ __ dxz, dyz __ dxy

  24. Ti3+ (d1) Mn2+ (d5) V3+ (d2) [M(H2O)6]n+ Fe2+ (d6) Co2+ (d7) Cr3+ (d3) Ni2+ (d8) Cu2+ (d9) Cr2+ (d4)

  25. d1 d2

  26. d3

  27. d3

  28. d4 d5

  29. d6

  30. d6

  31. d6

  32. d7

  33. d8 d9