1. The Period 4 transition metals

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

3. Aqueous oxoanions of transition elements Mn(II)Mn(VI)Mn(VII) V(V) Cr(VI) Mn(VII) 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(H 2 O) 6 ] 2+ [V(H 2 O) 6 ] 3+ [Cr(NH 3 ) 6 ] 3+ [Cr(NH 3 ) 5 Cl ] 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  is the splitting energy

10. The effect of ligand on splitting energy

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

12. What is electronic spectroscopy? Absorption Absorption of radiation leading to electronic transitions within a molecule or complex UV=higher energy transitions- between ligand orbitals visible=lower energy transitions- between d-orbitals of transition metals - between metal and ligand orbitals UV 400  nm (wavelength) 200700 visible Absorption ~14 00050 00025 000 UVvisible  cm -1 (frequency)  [Ru(bpy) 3 ] 2+ [Ni(H 2 O) 6 ] 2+ 10 10 4

13. Absorption maxima in a visible spectrum have three important characteristics 1.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,  oct or  tet and on the degree of inter-electron repulsion 3.intensity This depends on the "allowedness" of the transitions which is described by two selection rules

14. Energy of transitions molecular rotations lower energy (0.01 - 1 kJ mol -1 ) microwave radiation electron transitions higher energy (100 - 10 4 kJ mol -1 ) visible and UV radiation molecular vibrations medium energy (1 - 120 kJ mol -1 ) IR radiation Ground State Excited State During an electronic transition the complex absorbs energy electrons change orbital the complex changes energy state

15. [Ti(OH 2 ) 6 ] 3+ = d 1 ion, octahedral complex white light 400-800 nm blue: 400-490 nm yellow-green: 490-580 nm red: 580-700 nm 3+ Ti A / nm This complex is has a light purple colour in solution because it absorbs green light max = 510 nm Absorption of light

16. egeg t 2g oo h d-d transition [Ti(OH 2 ) 6 ] 3+ max = 510 nm  o is  243 kJ mol -1 20 300 cm -1 The energy of the absorption by [Ti(OH 2 ) 6 ] 3+ is the ligand-field splitting,  o An electron changes orbital; the ion changes energy state complex in electronic Ground State (GS) complex in electronic excited state (ES) GS ES GS ES egeg t 2g

17. Electron-electron repulsiond 2 ion egeg t 2g xyxzyz z2z2 x 2 -y 2 egeg t 2g xyxzyz z2z2 x 2 -y 2 xz + z 2 xy + z 2 lobes overlap, large electron repulsionlobes far apart, small electron repulsion x z x z y y These two electron configurations do not have the same energy

18. 3P3P 3F3F  E  E = 15 B B is the Racah parameter and is a measure of inter-electron repulsion within the whole ion States of the same spin multiplicity Relative strength of coupling interactions: M S =  m s > M L =  m l > M L - M S Which is the Ground State?

19. 2Eg2Eg 2 T 2g Effect of a crystal field on the free ion term of a d 1 complex 2T22T2 2E2E 6 Dq 4 Dq 2D2D tetrahedral fieldfree ionoctahedral field d 1  d 6

20.  2Eg2Eg 2 T 2g 2D2D Energy ligand field strength,  oct Energy level diagram for d 1 ions in an O h field For d 6 ions in an O h field, the splitting is the same, but the multiplicity of the states is 5, ie 5 E g and 5 T 2g

21. A / cm -1 - 30 00020 00010 000 d 1 oct [Ti(OH 2 ) 6 ] 3+ E LF strength Orgel diagram for d 1, d 4, d 6, d 9 0   D d 4, d 9 tetrahedral T 2g or T 2 d 4, d 9 octahedral E g or E d 1, d 6 tetrahedral E g or E d 1, d 6 octahedral 2 E g  2 T 2g 2Eg2Eg 2 T 2g 2D2D  

22. A / cm -1 - 30 00020 00010 000 [Ti(H 2 O) 6 ] 3+, d 1 2 T 2g 2Eg2Eg 2 B 1g 2 A 1g 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 d 34 A 2g d 5 (high spin) 6 A 1g d 6 (low spin) 1 A 1g d 83 A 2g Degenerate electronic ground state:T or E Non-degenerate ground state: A

23. Racah Parameters d 7 tetrahedral complex 15 B' = 10 900 cm -1 B' = 727 cm -1 [CoCl 4 ] 2- [Co(H 2 O) 6 ] 2+ d 7 octahedral complex 15 B' = 13 800 cm -1 B' = 920 cm -1 Free ion [Co 2+ ]: B = 971 cm -1 B' = 0.95 B B' = 0.75 B Nephelauxetic ratio,   is a measure of the decrease in electron-electron repulsion on complexation

24. - 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 - < H 2 O < NH 3 < en < [oxalate] 2- < [NCS] - < Cl - < Br - < I - Nephelauxetic series of metal ions Mn(II) Re (IV) < Fe(III) < Ir(III) < Co(III) < Mn(IV) cloud expanding The Nephelauxetic Effect

25. Selection Rules Transition  complexes Spin forbidden10 -3 – 1Many d 5 O h cxs Laporte forbidden [Mn(OH 2 ) 6 ] 2+ Spin allowed Laporte forbidden1 – 10Many O h cxs [Ni(OH 2 ) 6 ] 2+ 10 – 100 Some square planar cxs [PdCl 4 ] 2- 100 – 10006-coordinate complexes of low symmetry, many square planar cxs particularly with organic ligands Spin allowed10 2 – 10 3 Some MLCT bands in cxs with unsaturated ligands Laporte allowed 10 2 – 10 4 Acentric complexes with ligands such as acac, or with P donor atoms 10 3 – 10 6 Many CT bands, transitions in organic species

26. egeg t 2g egeg weak field ligands e.g. H 2 O high spin complexes strong field ligands e.g. CN - low spin complexes I - < Br - < S 2- < SCN - < Cl - < NO 3 - < F - < OH - < ox 2- < H 2 O < NCS - < CH 3 CN < NH 3 < en < bpy < phen < NO 2 - < phosph < CN - < CO The Spectrochemical Series The Spin Transition  

27. Tanabe-Sugano diagrams E/B  /B 2 T 2g 4 A 1g, 4 E 4 T 2g 4 T 1g 4 T 2g 4 T 1g 2 A 1g 4 T 2g 2 T 2g 6 A 1g 2Eg2Eg 4 A 2g, 2 T 1g 2 T 1g 2 A 1g 4Eg4Eg 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 Critical value of  d5d5 WEAK FIELDSTRONG FIELD

28. Tanabe-Sugano diagram for d 2 ions E/B  /B [V(H 2 O) 6 ] 3+ : Three spin allowed transitions 1 = 17 800 cm -1 visible 2 = 25 700 cm -1 visible 3 = obscured by CT transition in UV 10 000  30 000  cm -1  10 20 000 5 25 700=1.44 17 800  /B=32 3 = 2.1 1 = 2.1 x 17 800  3 = 37 000 cm -1 = 32

29. E/B  /B = 32 1 = 17 800 cm -1 2 = 25 700 cm -1 1 2 E/B = 43 cm -1 E/B = 30 cm -1 E/B = 43 cm -1 E = 25 700 cm -1 B=600 cm -1  o / B=32  o =19 200 cm -1

30. Tanabe-Sugano diagram for d 3 ions E/B  /B [Cr(H 2 O) 6 ] 3+ : Three spin allowed transitions 1 = 17 400 cm -1 visible 2 = 24 500 cm -1 visible 3 = obscured by CT transition 24 500=1.41 17 400  /B=24 3 = 2.1 1 = 2.1 x 17 400  3 = 36 500 cm -1 = 24

31. Calculating 3 E/B  /B 1 = 17 400 cm -1 2 = 24 500 cm -1 = 24 E/B = 34 cm -1 E/B = 24 cm -1 When 1 = E =17 400 cm -1 E/B = 24 so B = 725 cm -1 When 2 = E =24 500 cm -1 E/B = 34 so B = 725 cm -1 If  /B = 24  = 24 x 725 = 17 400 cm -1

32. TiF 4 d 0 ion TiCl 4 d 0 ion TiBr 4 d 0 ion TiI 4 d 0 ion d 0 and d 10 ion have no d-d transitions [MnO 4 ] - Mn(VII)d 0 ion [Cr 2 O 7 ] - Cr(VI)d 0 ion [Cu(MeCN) 4 ] + Cu(I)d 10 ion [Cu(phen) 2 ] + Cu(I)d 10 ion Zn 2+ d 10 ion extremely purple bright orange d 0 and d 10 ions white orange dark brown colourless dark orange white Charge Transfer Transitions

33. Ligand-to-metal charge transfer LMCT transitions Metal-to-ligand charge transfer MLCT transitions Md LL LL LL t 2g * eg*eg* d-d transitions