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Introduction to coordination chemistry

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Dr. Bhartendu K Srivastava (PhD)

This is a introductory presentation for the beginners who wish to understand the basics of coordination chemistry.

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Dr. BHARTENDU K SRIVASTAVA 1 Introduction to Coordination Chemistry Coordination Chemistry Chemistry of Coordination compounds Chemistry of complex ions NaCl H2O [Ni(H2O)6]2+NiCl2 H2O + 2Cl- NH3 [Ni(NH3)6]2+ + 2Cl-
Alfred Werner (Nobel Prize, 1913) developed a model of coordination complexes which explains the following observations. History: Werner's theory of Coordination complexes CoCl2 NH3 CoCl3.6NH3 Air CoCl3.5NH3 CoCl3.4NH3 CoCl3.3NH3 +2 +3 CoCl3.6NH3 aq. HCl Reactivity of ammonia got reduced CoCl3.6NH3 CoCl3.5NH3 CoCl3.4NH3 CoCl3.3NH3 aq. Ag+ 3 AgCl 2 AgCl 1 AgCl 0 AgCl Conductivity in aq. solution 4 ions 3 ions 2 ions 0 ions
Central metal in the coordination complex exhibits two types of valencies, primary valency (oxidation state) is ionisable and non directional, secondary valency (coordination number) is non ionisable and directional (directed towards fixed position in space), every metal has a fixed number Central metal tends to satisfy both primary valencies and secondary valencies [Co(NH3)6]Cl3 [Co(NH3)5Cl]Cl2 [Co(NH3)4Cl2]Cl [Co(NH3)3Cl3] [Co(NH3)6]3+ + 3Cl- [Co(NH3)5Cl]2+ + 2Cl- [Co(NH3)4Cl2]+ + Cl- [Co(NH3)3Cl3] + 0Cl- (neutral) [Co(NH3)6]3+ Coordination sphere Coordination number Central metal/Oxidation state Ligand 3+
Composition of complex entity Central metal ion Ligands Must have vacant d-orbitals (mostly d-block transition metals) Must have lone pair of electrons on the donor atom Monodentate (halides, ammines etc.) Chelating Ligands Bidentate (oxalate, ethylenediamine etc.) Polydentate (dien, EDTA etc.) Coordination number: Coordination number decides the geometry of the of the complexes C.N. = 2, Linear Geometry C.N. = 4, Tetrahedral, Square planar geometry C.N. = 6, Octahedral Geometry [M(L)n]3+
Nomenclature K4[Fe(CN)6] Potassium hexacyanoferrate(II) [Co(NH3)6]Cl3 Hexaamminecobalt(III) chloride [Pt(NH3)2Cl4] Diamminetetrachloroplatinum(IV) [Pt(NH3)4][PtCl4] Tetraammineplatinum(II)tetrachloroplatinate(II) [Pt(NH3)2Cl4] (Neutral) K4[Fe(CN)6] 4K+ + [Fe(CN)6]4- (Anionic) [Co(NH3)6]Cl3 [Co(NH3)6]3+ + 3Cl- (Cationic) [Pt(NH3)4][PtCl4] [Pt(NH3)4]2+ + [PtCl4]2-
Isomerism 2. Stereoisomerism a) Geometrical isomerism 1. Structural Isomerism a) Coordination isomerism [Co(NH3)6] [Cr(C2O4)3] [Cr(NH3)6] [Co(C2O4)3] b) Linkage isomerism [Co(ONO)(NH3)5]Cl [Co(NO2)(NH3)5]Cl c) Ionisation isomerism [PtBr(NH3)3]NO2 [Pt(NO2)(NH3)3]Br d) Hydrate isomerism [CrCl2(H2O)4]Cl.2H2O bright-green [CrCl(H2O)5]Cl2.H2O grey-green Square Planar Tetrahedral Octahedral Ma2b2 / Ma2bc/ M(ab)2 / Mabcd Ma2b4 / Ma4bc/ Ma3b3 / M(aa)2b2/M(aa)2bc/ Mabcdef [Pt(NH3)2Cl2]/Square Planar Cis trans Mabcd/ 3 isomers
Ma2b4 / Ma4bc/ Ma3b3 / M(aa)2b2/M(aa)2bc/ Mabcdef Ma2b4/[CrCl2(NH3)4]+ Cis/ violet trans/ green Ma3b3/[RhCl3py3] Cis form Trans form [Co(NH3)3(Cl)3]/Octahedral facial meridional
b) Optical isomerism Square Planar Tetrahedral Octahedral M(aa)3 / M(aa)2b2 /M(aa)2bc/ M(aa)b2c2/ Mabcdef two optically active isomeric form of the complex [Co(en)3]3+ Coordination complexes which can rotate plane of polarised light are optically active complexes. The essential thing is to not have a plane of symmetry.
Bonding in Coordination Complexes: Valence Bond Theory [Co(NH3)6]3+ C.N. = 6; O.S. = +3 (Diamagnetic) 27Co = [Ar] 3d7 4s2 Co3+ = [Ar] 3d6 4s0 Co(III) ion 6 empty orbitals for coordination number 6 3d 4s 4p 6 d2sp3 (equal energy) NH3 NH3 NH3 NH3 NH3 NH3 3+ Low Spin Complex
[CoF6]3- C.N. = 6; O.S. = +3(Paramagnetic) 27Co = [Ar] 3d7 4s2 Co3+ = [Ar] 3d6 4s0 Co(III) ion 3d 4s 4p 6 sp3d2 (equal energy)3- Valence Bond Theory: Shortcomings F- F- F- F- F- F- High Spin Complex 4d
Bonding in Coordination Complexes: Crystal Field Theory Bonding between a central metal ion and its ligand arises from purely electrostatic interactions 𝐵. 𝐸. = − 𝑞1 𝑞2 𝑟
6Dq 4Dq ∆ 𝑜 = 10Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Splitting Energy(∆ 𝑜) 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 4Dq∆ 𝑜 = 10Dq Crystal Field Splitting in octahedral complexes
6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 8Dq 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 12Dq ∆ 𝑜 = 10Dq ∆ 𝑜 = 10Dq
6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 16Dq 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 6Dq ∆ 𝑜 = 10Dq ∆ 𝑜 = 10Dq ∆ 𝒐 > P OR ∆ 𝒐 < PConcept of pairing energy ∆ 𝒐 > P; Low spin complex/ Strong field complex ∆ 𝒐 < P; High spin complex/ Weak field complex
eg t2g ENERGY State I State II State III eg t2g ENERGY State I State II State III Crystal Field Splitting energy∆ 𝑜 (F) ∆ 𝒐 > P; Low spin complex/ Strong field complex ∆ 𝒐 < P; High spin complex/ Weak field complex [CoF6]3- C.N. = 6; O.S. = +3(Paramagnetic) [Co(NH3)6]3+ C.N. = 6; O.S. = +3 (Diamagnetic) ∆ 𝑜 (NH3) > ∆ 𝑜 (F) ∆ 𝑜 (NH3)
4Dq 6Dq t2; E = 4 Dq e; E = -6 Dq ENERGY State I State II State III ∆𝑡 = − 4 9 ∆o 4Dq 6Dq t2; E = 4 Dq e; E = -6 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 6Dq Crystal Field Splitting in Tetrahedral complexes
Factors affecting the magnitude of crystal field splitting: Nature of Ligands: large negative charge, small size, good sigma donor and pi acceptors Oxidation state of the metal: higher for higher oxidation state Size of d orbitals: 5d > 4d > 3d Geometry of the complex: Crystal field splitting energy in octahedral Complexes will always be more than the tetrahedral complexes
Take home message • What kind of metals are involved in coordination complexes? • What kind of Ligands are involved in coordination complexes? • How to do naming of coordination compounds and do they possess isomerism? Nomenclature Isomerism • What kind of bonding is involved? theories and explanation VBT (Valence Bond Theory) CFT (Crystal Field Theory) • Therapeutic importance of coordination compounds
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Introduction to coordination chemistry

  • 1. Dr. BHARTENDU K SRIVASTAVA 1 Introduction to Coordination Chemistry Coordination Chemistry Chemistry of Coordination compounds Chemistry of complex ions NaCl H2O [Ni(H2O)6]2+NiCl2 H2O + 2Cl- NH3 [Ni(NH3)6]2+ + 2Cl-
  • 2. Alfred Werner (Nobel Prize, 1913) developed a model of coordination complexes which explains the following observations. History: Werner's theory of Coordination complexes CoCl2 NH3 CoCl3.6NH3 Air CoCl3.5NH3 CoCl3.4NH3 CoCl3.3NH3 +2 +3 CoCl3.6NH3 aq. HCl Reactivity of ammonia got reduced CoCl3.6NH3 CoCl3.5NH3 CoCl3.4NH3 CoCl3.3NH3 aq. Ag+ 3 AgCl 2 AgCl 1 AgCl 0 AgCl Conductivity in aq. solution 4 ions 3 ions 2 ions 0 ions
  • 3. Central metal in the coordination complex exhibits two types of valencies, primary valency (oxidation state) is ionisable and non directional, secondary valency (coordination number) is non ionisable and directional (directed towards fixed position in space), every metal has a fixed number Central metal tends to satisfy both primary valencies and secondary valencies [Co(NH3)6]Cl3 [Co(NH3)5Cl]Cl2 [Co(NH3)4Cl2]Cl [Co(NH3)3Cl3] [Co(NH3)6]3+ + 3Cl- [Co(NH3)5Cl]2+ + 2Cl- [Co(NH3)4Cl2]+ + Cl- [Co(NH3)3Cl3] + 0Cl- (neutral) [Co(NH3)6]3+ Coordination sphere Coordination number Central metal/Oxidation state Ligand 3+
  • 4. Composition of complex entity Central metal ion Ligands Must have vacant d-orbitals (mostly d-block transition metals) Must have lone pair of electrons on the donor atom Monodentate (halides, ammines etc.) Chelating Ligands Bidentate (oxalate, ethylenediamine etc.) Polydentate (dien, EDTA etc.) Coordination number: Coordination number decides the geometry of the of the complexes C.N. = 2, Linear Geometry C.N. = 4, Tetrahedral, Square planar geometry C.N. = 6, Octahedral Geometry [M(L)n]3+
  • 5. Nomenclature K4[Fe(CN)6] Potassium hexacyanoferrate(II) [Co(NH3)6]Cl3 Hexaamminecobalt(III) chloride [Pt(NH3)2Cl4] Diamminetetrachloroplatinum(IV) [Pt(NH3)4][PtCl4] Tetraammineplatinum(II)tetrachloroplatinate(II) [Pt(NH3)2Cl4] (Neutral) K4[Fe(CN)6] 4K+ + [Fe(CN)6]4- (Anionic) [Co(NH3)6]Cl3 [Co(NH3)6]3+ + 3Cl- (Cationic) [Pt(NH3)4][PtCl4] [Pt(NH3)4]2+ + [PtCl4]2-
  • 6. Isomerism 2. Stereoisomerism a) Geometrical isomerism 1. Structural Isomerism a) Coordination isomerism [Co(NH3)6] [Cr(C2O4)3] [Cr(NH3)6] [Co(C2O4)3] b) Linkage isomerism [Co(ONO)(NH3)5]Cl [Co(NO2)(NH3)5]Cl c) Ionisation isomerism [PtBr(NH3)3]NO2 [Pt(NO2)(NH3)3]Br d) Hydrate isomerism [CrCl2(H2O)4]Cl.2H2O bright-green [CrCl(H2O)5]Cl2.H2O grey-green Square Planar Tetrahedral Octahedral Ma2b2 / Ma2bc/ M(ab)2 / Mabcd Ma2b4 / Ma4bc/ Ma3b3 / M(aa)2b2/M(aa)2bc/ Mabcdef [Pt(NH3)2Cl2]/Square Planar Cis trans Mabcd/ 3 isomers
  • 7. Ma2b4 / Ma4bc/ Ma3b3 / M(aa)2b2/M(aa)2bc/ Mabcdef Ma2b4/[CrCl2(NH3)4]+ Cis/ violet trans/ green Ma3b3/[RhCl3py3] Cis form Trans form [Co(NH3)3(Cl)3]/Octahedral facial meridional
  • 8. b) Optical isomerism Square Planar Tetrahedral Octahedral M(aa)3 / M(aa)2b2 /M(aa)2bc/ M(aa)b2c2/ Mabcdef two optically active isomeric form of the complex [Co(en)3]3+ Coordination complexes which can rotate plane of polarised light are optically active complexes. The essential thing is to not have a plane of symmetry.
  • 9. Bonding in Coordination Complexes: Valence Bond Theory [Co(NH3)6]3+ C.N. = 6; O.S. = +3 (Diamagnetic) 27Co = [Ar] 3d7 4s2 Co3+ = [Ar] 3d6 4s0 Co(III) ion 6 empty orbitals for coordination number 6 3d 4s 4p 6 d2sp3 (equal energy) NH3 NH3 NH3 NH3 NH3 NH3 3+ Low Spin Complex
  • 10. [CoF6]3- C.N. = 6; O.S. = +3(Paramagnetic) 27Co = [Ar] 3d7 4s2 Co3+ = [Ar] 3d6 4s0 Co(III) ion 3d 4s 4p 6 sp3d2 (equal energy)3- Valence Bond Theory: Shortcomings F- F- F- F- F- F- High Spin Complex 4d
  • 11. Bonding in Coordination Complexes: Crystal Field Theory Bonding between a central metal ion and its ligand arises from purely electrostatic interactions 𝐵. 𝐸. = − 𝑞1 𝑞2 𝑟
  • 12. 6Dq 4Dq ∆ 𝑜 = 10Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Splitting Energy(∆ 𝑜) 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 4Dq∆ 𝑜 = 10Dq Crystal Field Splitting in octahedral complexes
  • 13. 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 8Dq 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 12Dq ∆ 𝑜 = 10Dq ∆ 𝑜 = 10Dq
  • 14. 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 16Dq 6Dq 4Dq eg; E = 6 Dq t2g; E = -4 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 6Dq ∆ 𝑜 = 10Dq ∆ 𝑜 = 10Dq ∆ 𝒐 > P OR ∆ 𝒐 < PConcept of pairing energy ∆ 𝒐 > P; Low spin complex/ Strong field complex ∆ 𝒐 < P; High spin complex/ Weak field complex
  • 15. eg t2g ENERGY State I State II State III eg t2g ENERGY State I State II State III Crystal Field Splitting energy∆ 𝑜 (F) ∆ 𝒐 > P; Low spin complex/ Strong field complex ∆ 𝒐 < P; High spin complex/ Weak field complex [CoF6]3- C.N. = 6; O.S. = +3(Paramagnetic) [Co(NH3)6]3+ C.N. = 6; O.S. = +3 (Diamagnetic) ∆ 𝑜 (NH3) > ∆ 𝑜 (F) ∆ 𝑜 (NH3)
  • 16. 4Dq 6Dq t2; E = 4 Dq e; E = -6 Dq ENERGY State I State II State III ∆𝑡 = − 4 9 ∆o 4Dq 6Dq t2; E = 4 Dq e; E = -6 Dq ENERGY State I State II State III Crystal Field Stabilization Energy = 6Dq Crystal Field Splitting in Tetrahedral complexes
  • 17. Factors affecting the magnitude of crystal field splitting: Nature of Ligands: large negative charge, small size, good sigma donor and pi acceptors Oxidation state of the metal: higher for higher oxidation state Size of d orbitals: 5d > 4d > 3d Geometry of the complex: Crystal field splitting energy in octahedral Complexes will always be more than the tetrahedral complexes
  • 18. Take home message • What kind of metals are involved in coordination complexes? • What kind of Ligands are involved in coordination complexes? • How to do naming of coordination compounds and do they possess isomerism? Nomenclature Isomerism • What kind of bonding is involved? theories and explanation VBT (Valence Bond Theory) CFT (Crystal Field Theory) • Therapeutic importance of coordination compounds
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