Coordination Chemistry

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1 Coordination Chemistry 1893 To central atom, more ligands can be bound then is its oxidation number Alfred Werner ( ) P in Chemistry 1913 [Co II (gly) 3 ] - 1

2 Coordination Compounds [Co(H 3 ) 6 ]Cl 3 [Co(H 3 ) 5 Cl]Cl 2 [Co(H 3 ) 4 Cl 2 ]Cl Metal in oxidation state n+ (primary valence) Complex has coordination number m (secondary valence) Ligands bound to central atom by donor-acceptor bonds 2

Coordination Compounds n+/- Ligands X +/- n Complex charge Central cation / metal atom Anion/cation (opposite charge) Central metal cation / neutral atom

3 Coordination Compounds n+/- Ligands X +/- n Complex charge Central cation / metal atom Anion/cation (opposite charge) Central metal cation / neutral atom surrounded by a set of ligands. Each ligand provides 2 electrons to empty d-orbitals at metal and forms donor-acceptor bond. umber of ligands = Coordination number 3

4 Inner and uter Coordination Sphere Inner Coordination Sphere = ligands driectly bound to the central atom uter Coordination Sphere = ions asociated with a complex, not bound uter Coordination Sphere Inner Coordination Sphere counterion H 2 S 4 2- H 2 ligand H 2 H 2 Mn 2+ H 2 H 2 Mn 2+ S 3 H 2 H 2 H 2 H 2 H 2 [Mn(H 2 ) 5 (S 4 ) 5 ]: Inner Coordination of S 4 2- [Mn(H 2 ) 6 ][S 4 ]: outer coordination of S 4 2-4

5 Coordination Compounds K 2 [PtCl 6 ] 5

6 Energy Level rdering Ar [e] 3s 2 3p 6 (4s 0 ) K [Ar] 4s 1 (3d 0 4p 0 ) Ca [Ar] 4s 2 (3d 0 4p 0 ) Sc [Ar] 3d 1 4s 2 (4p 0 ) Ti [Ar] 3d 2 4s 2 (4p 0 ) 6

7 Stability of Half- / Filled d-rbitals Cr [Ar] 3d 5 4s 1 (4p 0 ) Cu [Ar] 3d 10 4s 1 (4p 0 ) 7

8 xidation States of TMs Sc Ti V Cr Mn Fe Co i Cu Zn 3 2,3 4 1,2,3 4,5 1,2, 3,4, 5,6 1,2, 3,4, 5,6,7 2,3, 4,5,6 1,2,3,4 1,2 3,4 1,2 2 8

9 d-electron Count umber of electrons in valence level Cr [Ar] 3d 5 4s 1 (4p 0 ) umber of electrons removed during cationt formation: electrons of s-orbital are removed first Cr 3+ umber of electrons remaining in d- orbitals Cr 3+ [Ar] 3d 3 4s 0 (4p 0 ) Cr 3+ is a d 3 cation 9

10 ox = en = H 2 H 2 Complex x.o. (Ligand) x.o. (M) o. d-electrons [Cr 2 7 ] d 0 [Mn 4 ] d 0 [Ag(H 3 ) 2 ] d 10 [Ti(H 2 ) 6 ] d 1 [Co(en) 3 ] d 6 [PtCl 2 (H 3 ) 2 ] -1, 0 +2 d 8 [V(C) 6 ] d 3 [Fe(ox) 3 ] d 5 10

11 Donor-Acceptor Bond donor-acceptor bond is equivalent to a covalent bond Acceptor Empty orbital Donor Free e pair Covalent Bond 11

12 VB theory H H H + F Donor-Acceptor Bond B F F F H F B H F H F H F B H F H H 3 + BF 3 H 3 _ > BF 3 Donor-Acceptor Bond 12

13 Donor-Acceptor Bond H 3 + BF 3 H 3 _ > BF 3 VB theory F F F F F F F F F H H H H H H H H H B M theory 13

14 VB theory Donor-Acceptor Bond "Lewis Base" [Co(H 3 ) 6 ] 3+ H H H H + Co 3+ H 3 H 3 H 3 H 3 Each ligand provides 2 electrons "Lewis Acid" H 3 14

15 Pt 2+ [Xe] 4f 14 5d 8 4s 0 d s p PtCl 4 2- dsp 2 hybrid orbitals Electrons from Cl -, square planar d s p i 2+ [Ar] 3d 8 4s 0 icl 4 2- sp 3 hybrid orbitals Electrons from Cl -, tetrahedral 15

16 Co 3+ [Ar] 3d 6 4s 0 d s p CoF 6 3- Co 3+ [Ar] 3d 6 4s 0 Co(H 3 ) 6 3+ d s sp 3 d 2 hybrid orbitals Electrons from F -, octahedral p L L L L L d 2 sp 3 hybrid orbitals Electrons from H 3, octahedral L 16

17 Monodentate Ligands C Carbon dioxide Cr C i(c) 4, Fe(C) 5, Mo(C) 6 H 3 ammonia P PPh 3 phosphane H 2 water SR 2 thioether 17

18 HSAB = Hard and Soft Acids and Bases R. Pearson 1963 High oxidation states of central atoms are stabilised by F, 2 Low oxidation states are stabilised by C, C Hard Soft Acid Base 18

19 HARD donor atoms HSAB SFT donor atoms H 3, F -, H 2, H -, C 2-3 Small donor atoms High electronegativity Difficult to polarize Weak C, PPh 3, I -, C 2 H 4, SRH, C -, SC - Large donor atoms Low electronegativity Easily polarized Stabile complexes complexes Stabile complexes Hard metals Fe(III), Mg(II), Cr(III), Al(III) Small atoms (1st trans. row) Large charge Soft metals Ag(I), Cu(I), Hg(II), Au(I) Large atoms (2nd and 3rd transition row) Small charge 19

20 eutral Bidentate Ligands H 2 H 2 [PtCl 2 (en)] Five-membered chelate cycle square planar complex 1,2-diaminoethane = ethylendiamine = en Ph 2 P PPh 2 1,2-difenylphosphinoethane dppe 2,2'-bipyridine bipy 1,10-phenanthroline phen 20

21 Anionic Bidentate Ligands H 3 C acetate = ac oxalate = ox 2- R R 1 H Pd H R 1 complex Pd(II)-oxim R π-donor bidentate ligand Fe C C C [Fe(C) 3 (h 4 -C 4 H 6 )] 21

22 Tridentate Ligands H 2 H H 2 diethylentriamine dien 2,2':6',2"-terpyridine tpy 1,2,4-triazacyclononane Macrocyclic ligand H H H 22

23 Tetradentate Ligands H 2 H 2 H 2 tris(2-aminoethyl)amine tren H H H H porfyrine ftalocyanine 23

24 Multidentate Ligands tetraanion of ethylendiamintetraacetic acid EDTA M Hexadentate 24

25 omenclature of Coordination Complexes H 2 -Aqua H 3 -Ammine C-Carbonyl -itrosyl CH 3 H 2 -Methylamine C 5 H 5 -Pyridine F - -Fluoro Cl - -Chloro Br--Bromo I - -Iodo 2- -xo H - -Hydroxo C - -Cyano S Sulfato S Thiosulfato 2- -itrito-- - -itrito-- SC - -Thiocyanato-S- CS - -Thiocyanato-- 25

26 Stability of Complexes Stability constant of a complex = equilibrium constant of its formation High value of K = stabile complex 26

27 Stability of Complexes Stability constant of a complex ML n 27

28 Stability of Complexes Total stability constant of a complex ML n 28

29 Chelate Effect logk = 8.61 [i(h 2 ) 6 ] H 3 [i(h 3 ) 6 ] H 2 logk = [i(h 2 ) 6 ] en [i(en) 3 ] H 2 ΔG = - RT lnk = ΔH - TΔS ΔH same for both reactions (i- i-) ΔS high for chelate, more product particles 29

30 Chelates, Macrocycles, Cryptates P in Chemistry 1987 Donald J. Cram Jean-Marie Lehn Charles J. Pedersen 30

31 Chelates, Macrocycles, Cryptates EDTA tetraanion of ethylendiamintetraacetic acid CH CH HC CH Co Chelatation therapy of Pb poisoning Chelatometry Dissolves CaC 3 31

32 Chelates, Macrocycles, Cryptates Metalloporphyrins: M = Fe (hem, cytochrom c), Mg (chlorophyl), Co (B 12 ) R 9 R 8 R 1 R 7 R 2 R 12 M R 10 R 6 R 3 R 5 R 11 R 4 32

33 Hemoglobine 33

34 6C 2 + 6H 2 C 6 H Mg chlorophyl 34

35 Chelates, Macrocycles, Cryptates Valinomycine 35

36 Geometry of Complexes L L L L L M L L L M L L ctahedral complexes h Tetrahedral complexs T d 36

37 Geometry of Complexes Tetrahedral 109 o 28' C.. 4 Square planar 90 o C.. 4 Trigonal bipyramidal 120 o + 90 o C.. 5 Square pyramidal 90 o C.. 5 ctahedral 90 o C

38 Isomers of Complexes Structural isomers Bonding Coordination Ionization Stereo isomers Geometric ptical 38

39 Structural Isomers Bonding : SC -, 2-, C H 3 H 3 H 3 H 3 Co H 3 H 3 H 3 H 3 H 3 Co H 3 nitro- nitrito- 39

40 Structural Isomers Coordination [Pt(H 3 ) 4 ][CuCl 4 ] [Cu(H 3 ) 4 ][PtCl 4 ] Ionization [Co(H 3 ) 5 S 4 ]Br [Co(H 3 ) 5 Br]S 4 40

41 Stereo Isomers Geometric: cis-trans, diastereomers 41

42 Stereo Isomers Geometric: cis-trans diastereomers cis trans Cl H 3 H 3 Pt Cl Cl Pt Cl H 3 H 3 42

43 Antitumor Medicine H 3 Cl Pt H 3 Cl Cisplatin H 3 H 3 Pt Carboplatin H 3 H 3 Pt edaplatin H 2 Pt H 2 xaliplatin Inactive H 2 H 3 Cl Cl Pt Pt H 3 H Cl H 2 43

44 Cisplatin = cancerostatics Stereo Isomers H 2 H H 3 H H Pt H 3 H H H H H 2 P - H H DA H P H H - 44

45 Stereo Isomers Geometric: mer-fac, diastereomers fac A B mer A B A M B A M B A B B A S fac mer S L S M L M L L L L 45

46 ptical: enantiomers Stereo Isomers 46

47 ptical: enantiomers Stereo Isomers [Co(en) 3 ] 3+ o S n S 1 = symmetry plane S 2 = inversion center 47

48 ptical Rotation 48

49 1) VB Bonding in Complexes 2) CFT = Crystal Field Theory 1929 Hans Bethe Electrostatic interactions between ligands and metal 3) LFT = Ligand Field Theory 1935 modification J. H. Van Vleck covalence 4) M 49

50 ctahedral complex Ligand Field Theory z Central atom in the center of octahedron y x Ligands as negative point charges 50

51 d-rbitals in ctahedral Ligand Field 51

52 Splitting of d-levels in h Field e g Destabilization 0.6 Δ o 5 degenerate d-orbitals in isolated cation t 2g Stabilization 0.4 Δ o 52

53 CFSE = Crystal Field Stabilization Energy Δ o Δ o Weak field Δ o < P (pairing energy) High spin complexes Strong field Δ o > P (pairing energy) Low spin complexes 53

54 Crystal Field Stabilization Energy Weak field Strong field Δ o increases 54

55 Weak field Strong field e CFSE e CFSE d 1 t 2g Δ o t 2g Δ o d 2 t 2g Δ o t 2g Δ o d 3 t 2g Δ o t 2g Δ o d 4 t 2g 3 e g Δ o t 2g Δ o d 5 t 2g 3 e g Δ o t 2g Δ o d 6 t 2g 4 e g Δ o t 2g Δ o d 7 t 2g 5 e g Δ o t 2g 6 e g Δ o d 8 t 2g 6 e g Δ o t 2g 6 e g Δ o CFSE = (n t 2g ) 0.4 Δ o (n e g ) 0.6 Δ o e = number of unpaired electrons 55

56 Splitting of d-levels in h Field e g 3/5Δ o 2/5Δ o 10Dq t 2g [Ti(H 2 ) 6 ] 3+ d 1 t 2g1 e g 0 t 2g e g 1 pink 243 kj mol 1 (Δ o ) 56

57 UV-vis Absorption Spectrum of [Ti(H 2 ) 6 ] 3+ 57

58 Electronic Transitions Electronic Transition This energy is just sufficient to excite electron Energy increases 58

59 59

60 Splitting of d-levels in T d Field t 2 2/5Δ t 3/5Δ t e Δ t = 4/9 Δ o T d complexes are always high spin o d-orbital points directly to ligands = weaker interaction 60

61 d-rbitals in Tetrahedral Ligand Field 61

62 Splitting of d-levels in Square Planar Field (d 8 ) i(c) 4 2-,PdCl 4 2-, x2 -y2 x 2 -y2 b 1g Pt(H 3 ) 4 2+,PtCl 4 2-, e g AuCl 4 - z 2 xy b 2g t 2g xy z 2 a 1g d 8 xz, yz xz, yz e g Removing ligands in z direction 62

63 18-electron Rule umber of d-electrons of neutral metal + 2 e neutral ligands + 1 e anionic ligands Sum 18 for stabile complexes Cr(C) 6 Cr d 6 6 C 6 2 = 12 Sum 18 [Co(H 3 ) 3 Cl 3 ] Co d 9 3 H = 6 3 Cl 3 1 = 3 Sum 18 63

64 Properties of Complexes e g Ligand field splitting t 2g 64

65 Spectrochemical Series: Ligand Field Splitting Factors I - < Br - < S 2- < SC - < Cl - < 3-, F - < H - < ox, 2- < H 2 < CS - < py, H 3 < en < bpy, phen < 2- < CH 3-, C 6 H 5- < C - < C Central atom: 3d < 4d < 5d 2+ < 3+ < 4+ Mn 2+ < i 2+ < Co 2+ < Fe 2+ < V 2+ < Fe 3+ < Co 3+ < Mn 3+ < Mo 3+ < Rh 3+ < Ru 3+ < Pd 4+ < Ir 3+ < Pt 4+ Type of coordination 4/9 Δ = Δ t Bond length and strength M-L 65

66 66

67 Bonding in Complexes by M 3 x np 1x ns 5x (n 1) d rbitals of metal SALCA rbitals of ligands 67

68 Metal Valence rbitals z s p x p y p z d xy d xz d yz x y d x2-y2 d z2 68

69 e g 3 x np t 1u M-L Sigma bonds a 1g 69

70 onbonding d-rbitals t 2g There is no suitable combination of As of ligands (for sigma bonding) 70

71 71

72 t 1u * (n+1)p t 1u a 1g * (n+1)s a 1g e g * nd e g,t 2g Δ o t 2g a 1g, e g, t 1u e g t 1u a 1g M ML 6 6L 72

73 t 2 * (n+1)p t 2 a 1 * (n+1)s a 1 t 2 * nd e, t 2 Δ t e a 1, t 2 a 1 t 2 M ML 4 4L(LGs) 73

74 (n+1)p a 2u,e u e u * a 1g * a 2u (n+1)s a 1g b 1g * a 1g nd e g,a 1g,b 1g,b 2g Δ b 2g,e g a 1g, e g, t 1u e u b 1g M ML 4 (D 4h ) 4L(LGs) a 1g 74

75 M in π-bonding pπ-dπ R -, RS -, 2-, F -, Cl -, Br -, I -, R 2 - dπ-dπ R 3 P, R 3 As, R 3 S C H H dπ-π* C, RC, pyridine, C -, 2, 2 -, ethylene dπ-σ* H 2, R 3 P, alkanes 75

76 Pi base Pi acid 76

77 Ligands with pi rbitals Pi base Pi acid 77

78 Back pi donation M C Sigma donation M C 78

79 Kinetics [M(H 2 ) n ] x+ + H 2 * [M(H 2 * )(H 2 ) n-1 ] x+ + H 2 τ (s) H IERT Metal ion Ir Rh Cr Ru Ru 2+ Be At Fe Ga V i Mg Ti In Tm Yb Fe V Co Mn K Rb a+ Cs Li + + Ca Er Sr Ba Ho 3+ Cr Dy Tb Gd Cu LABILE Pt 2+ Pd Zn Cd Hg k H 2 (s ) 79

80 Mechanisms of Complex Reactions Mechanism Dissociative (D) W(C) 6 W(C) + 5 C W(C) + 5 PPh 3 W(C) 5 (PPh 3 ) Associative (A) [i(c) 4 ] C - [i(c) 4 ( 14 C) ] 3- [i(c) 4 ( 14 C) ] 3- [i(c) 3 ( 14 C) ] 2- + C - 80

81 81

Electronic structure Crystal-field theory Ligand-field theory. Electronic-spectra electronic spectra of atoms

Electronic structure Crystal-field theory Ligand-field theory. Electronic-spectra electronic spectra of atoms Chapter 19 d-metal complexes: electronic structure and spectra Electronic structure 19.1 Crystal-field theory 19.2 Ligand-field theory Electronic-spectra 19.3 electronic spectra of atoms 19.4 electronic