The Period 4 transition metals

1. The Period 4 transition metals

2. Colors of representative compounds of the Period 4 transition metals nickel(II) nitrate hexahydrate sodium chromate zinc sulfate heptahydrate potassium ferricyanide titanium oxide scandium oxide manganese(II) chloride tetrahydrate copper(II) sulfate pentahydrate vanadyl sulfate dihydrate cobalt(II) chloride hexahydrate

3. Mn(II) Mn(VI) Mn(VII) Mn(VII) Cr(VI) V(V) Aqueous oxoanions of transition elements One of the most characteristic chemical properties of these elements is the occurrence of multiple oxidation states.

4. Effects of the metal oxidation state and of ligand identity on color [V(H2O)6]3+ [V(H2O)6]2+ [Cr(NH3)6]3+ [Cr(NH3)5Cl]2+

5. Linkage isomers

6. An artist’s wheel

8. The five d-orbitals in an octahedral field of ligands

9. Splitting of d-orbital energies by an octahedral field of ligands D is the splitting energy

10. The effect of ligand on splitting energy

11. Electronic Spectroscopy of Transition Metal Complexes Chemistry 412 Experiment 1

12. - n / cm-1 (frequency) What is electronic spectroscopy? Absorption of radiation leading to electronic transitions within a molecule or complex Absorption Absorption [Ru(bpy)3]2+ [Ni(H2O)6]2+ 104 10 ~14 000 25 000 50 000 200 400 700 visible UV UV visible l / nm (wavelength) UV = higher energy transitions - between ligand orbitals visible = lower energy transitions - between d-orbitals of transition metals - between metal and ligand orbitals

13. Absorption maxima in a visible spectrum have three important characteristics number (how many there are) This depends on the electron configuration of the metal centre 2. position (what wavelength/energy) This depends on the ligand field splitting parameter, Doct or Dtet and on the degree of inter-electron repulsion intensity This depends on the "allowedness" of the transitions which is described by two selection rules

14. Energy of transitions Excited State molecular rotations lower energy (0.01 - 1 kJ mol-1) microwave radiation electron transitions higher energy (100 - 104 kJ mol-1) visible and UV radiation Ground State molecular vibrations medium energy (1 - 120 kJ mol-1) IR radiation During an electronic transition the complex absorbs energy electrons change orbital the complex changes energy state

15. 3+ Ti Absorption of light [Ti(OH2)6]3+ = d1 ion, octahedral complex white light 400-800 nm blue: 400-490 nm yellow-green: 490-580 nm red: 580-700 nm A This complex is has a light purple colour in solution because it absorbs green light l / nm lmax = 510 nm

16. The energy of the absorption by [Ti(OH2)6]3+ is the ligand-field splitting, Do ES ES eg eg hn Do GS GS t2g t2g d-d transition complex in electronic excited state (ES) complex in electronic Ground State (GS) [Ti(OH2)6]3+lmax = 510 nm Do is  243 kJ mol-1 20 300 cm-1 An electron changes orbital; the ion changes energy state

17. d2 ion Electron-electron repulsion eg eg x2-y2 x2-y2 z2 z2 t2g t2g xy xz yz xy xz yz xy + z2 xz + z2 z z y y x x lobes overlap, large electron repulsion lobes far apart, small electron repulsion These two electron configurations do not have the same energy

18. MS = S ms ML = S ml ML - MS > > Which is the Ground State? 3P States of the same spin multiplicity D E 3F D E = 15 B B is the Racah parameter and is a measure of inter-electron repulsion within the whole ion Relative strength of coupling interactions:

19. 6 Dq 4 Dq Effect of a crystal field on the free ion term of a d1 complex d1 d6 tetrahedral field free ion octahedral field 2Eg 2T2 2D 2E 2T2g

20. Energy level diagram for d1 ions in an Oh field 2Eg Energy D 2D 2T2g ligand field strength, Doct For d6 ions in an Oh field, the splitting is the same, but the multiplicity of the states is 5, ie5Eg and 5T2g

21. A D Orgel diagram for d1, d4, d6, d9 10 000 20 000 30 000 Eg or E E T2g or T2 D - n / cm-1 T2g or T2 D Eg or E d1, d6 octahedral D d1, d6 tetrahedral D 0 d4, d9 octahedral d4, d9 tetrahedral LF strength [Ti(OH2)6]3+ d1oct 2Eg 2Eg 2T2g 2D 2T2g

22. - n / cm-1 The Jahn-Teller Distortion: Any non-linear molecule in a degenerate electronic state will undergo distortion to lower it's symmetry and lift the degeneracy Degenerate electronic ground state: T or E Non-degenerate ground state: A d34A2g d5 (high spin) 6A1g d6 (low spin) 1A1g d83A2g 2B1g A 2Eg [Ti(H2O)6]3+, d1 2A1g 2T2g 10 000 20 000 30 000

23. Racah Parameters Free ion [Co2+]: B = 971 cm-1 [Co(H2O)6]2+ [CoCl4]2- d7 octahedral complex 15 B' = 13 800 cm-1 B' = 920 cm-1 d7 tetrahedral complex 15 B' = 10 900 cm-1 B' = 727 cm-1 B' = 0.95 B B' = 0.75 B Nephelauxetic ratio, b b is a measure of the decrease in electron-electron repulsion on complexation

24. The Nephelauxetic Effect cloud expanding • some covalency in M-L bonds – M and L share electrons • effective size of metal orbitals increases • electron-electron repulsion decreases Nephelauxetic series of ligands F- < H2O < NH3 < en < [oxalate]2- < [NCS]- < Cl- < Br- < I- Nephelauxetic series of metal ions Mn(II) < Ni(II) Co(II) < Mo(II) > Re (IV) < Fe(III) < Ir(III) < Co(III) < Mn(IV)

25. Selection Rules Transition e complexes Spin forbidden 10-3 – 1 Many d5 Oh cxs Laporte forbidden [Mn(OH2)6]2+ Spin allowed Laporte forbidden 1 – 10 Many Oh cxs [Ni(OH2)6]2+ 10 – 100 Some square planar cxs [PdCl4]2- 100 – 1000 6-coordinate complexes of low symmetry, many square planar cxs particularly with organic ligands Spin allowed 102 – 103 Some MLCT bands in cxs with unsaturated ligands Laporte allowed 102 – 104 Acentric complexes with ligands such as acac, or with P donor atoms 103 – 106 Many CT bands, transitions in organic species

26. The Spectrochemical Series eg eg I- < Br- < S2- < SCN- < Cl-< NO3- < F- < OH- < ox2- < H2O < NCS- < CH3CN < NH3 < en < bpy < phen < NO2- < phosph < CN- < CO D D t 2g t 2g weak field ligands e.g. H2O high spin complexes strong field ligands e.g. CN- low spin complexes The Spin Transition

27. WEAK FIELD STRONG FIELD d5 Tanabe-Sugano diagrams 4T2g 2A1g E/B 4T1g All terms included Ground state assigned to E = 0 Higher levels drawn relative to GS Energy in terms of B High-spin and low-spin configurations 4Eg 4T2g 4A1g, 4E 2A1g 2T1g 2T2g 2Eg Critical value of D 4A2g, 2T1g 4T2g 6A1g 4T1g 2T2g D/B

28. 10 e 5 30 000 20 000 10 000 D/B = 32 - n / cm-1 n3 = 2.1n1 = 2.1 x 17 800 n3 = 37 000 cm-1 = 32 Tanabe-Sugano diagram for d2 ions [V(H2O)6]3+: Three spin allowed transitions E/B n1 = 17 800 cm-1 visible n2 = 25 700 cm-1 visible n3 = obscured by CT transition in UV 25 700 = 1.44 17 800 D/B

29. n2 E/B = 43 cm-1 n1 E/B = 30 cm-1 D/B = 32 E/B n1 = 17 800 cm-1 n2 = 25 700 cm-1 E/B = 43 cm-1 E = 25 700 cm-1 B = 600 cm-1 Do / B = 32 Do = 19 200 cm-1

30. 24 500 = 1.41 17 400 n3 = 2.1n1 = 2.1 x 17 400 n3 = 36 500 cm-1 = 24 Tanabe-Sugano diagram for d3 ions n1 = 17 400 cm-1 visible n2 = 24 500 cm-1 visible n3 = obscured by CT transition [Cr(H2O)6]3+: Three spin allowed transitions E/B D/B = 24 D/B

31. E/B = 34 cm-1 E/B = 24 cm-1 Calculating n3 n1 = 17 400 cm-1 n2 = 24 500 cm-1 E/B When n1 = E =17 400 cm-1 E/B = 24 so B = 725 cm-1 When n2 = E =24 500 cm-1 E/B = 34 so B = 725 cm-1 If D/B = 24 D = 24 x 725 = 17 400 cm-1 D/B = 24

32. Charge Transfer Transitions d0 and d10 ions d0 and d10 ion have no d-d transitions white Zn2+ d10 ion TiF4 d0 ion TiCl4 d0 ion TiBr4 d0 ion TiI4 d0 ion white white orange dark brown [MnO4]- Mn(VII) d0 ion [Cr2O7]- Cr(VI) d0 ion extremely purple bright orange [Cu(MeCN)4]+ Cu(I) d10 ion [Cu(phen)2]+ Cu(I) d10 ion colourless dark orange

33. d-d transitions Metal-to-ligand charge transfer MLCT transitions Ligand-to-metal charge transfer LMCT transitions Charge Transfer Transitions Lp* eg* t2g* Md Lp Ls