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Coordination Chemistry

Coordination Chemistry. Biological systems, e.g., heme. Coordination Chemistry. Alfred Werner (1866-1919) 1893, age 26: coordination theory Nobel prize for Chemistry, 1913 Addition of 6 mol NH 3 to CoCl 3 (aq) Conductivity studies Precipitation with AgNO 3. Atkins, Jones, p. 934

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Coordination Chemistry

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  1. Coordination Chemistry Biological systems, e.g., heme

  2. Coordination Chemistry Alfred Werner (1866-1919) 1893, age 26: coordination theory Nobel prize for Chemistry, 1913 Addition of 6 mol NH3 to CoCl3(aq) Conductivity studies Precipitation with AgNO3 Atkins, Jones, p. 934 Chang, p. 883 Miessler, Tarr, p. 278 Mortimer, p. 723 Whitten et al., p. 893

  3. Werner Coordination Theory Compound Moles of ions Moles of AgCl(s) “CoCl3.6NH3” 4 3 “CoCl3.5NH3” 3 2 “CoCl3.4NH3” 2 1 “CoCl3.3NH3” 0 0 Cl– attached to NH3 may be dissociated

  4. Werner Coordination Theory Proposed six ammonia molecules to covalently bond to Co3+ Compound Moles of ions Moles of AgCl(s) [Co(NH3)6]Cl3 4 3 [Co(NH3)5Cl]Cl2 3 2 [Co(NH3)4Cl2]Cl 2 1 [Co(NH3)3Cl3] 0 0

  5. Coordination Chemistry Definitions Coordination compounds– compounds composed of a metal atom or ion and one or more ligands (atoms, ions, or molecules) that are formally donating electrons to the metal center Miessler, Tarr, p. 278

  6. Coordination Chemistry Definitions Coordination compounds M 3Cl– (counterion) ligand (coordination sphere) N forms a coordinate covalent bond to the metal

  7. Coordination Chemistry Definitions Ligands– simple, ‘complex’ Denticity – different number of donor atoms Chelates – compounds formed when ligands are chelating (Gk. crab’s claw) M bidentate

  8. Coordination Chemistry edta4–, [(OOCCH2)2NH2NH2(CH2COO)2]4– Cr N O [Cr(edta)]–

  9. Valence Bond Theory Metal or metal ion: Lewis acid Ligand: Lewis base Hybridization of s, p, d orbitals C.N. Geometry Hybrids 4 tetrahedral sp3 4 square planar dsp2 5 trigonal bipyramidal dsp3 or sp3d 6 octahedral d2sp3 or sp3d2

  10. Valence Bond Theory Example 1: [Co(NH3)6]3+ Co [Ar] 3d7 4s2 Co3+ [Ar] 3d6 3d 4s 4p d2sp3 4d if complex is diamagnetic : octahedral

  11. Valence Bond Theory Example 2: [CoF6]3– Co [Ar] 3d7 4s2 Co3+ [Ar] 3d6 3d 4s 4p 4sp3d2 4d octahedral if complex is paramagnetic

  12. Valence Bond Theory Example 3: [PtCl4]2–, diamagnetic Pt2+ [Xe] 4f14 5d8 5d 6s 6p dsp2 square planar

  13. Valence Bond Theory Example 4: [NiCl4]2–, tetrahedral Ni2+ [Ar] 3d8 3d 4s 4p 4sp3 paramagnetic

  14. Valence Bond Theory Ligands (Lewis base) form coordinate covalent bonds with metal center (Lewis acid) Relationship between hybridization, geometry, and magnetism Inadequate explanation for colors of complex ions e.g., [Cr(H2O)6]3+, [Cr(H2O)4Cl2]+

  15. Crystal Field Theory Basis: purely electrostatic interaction Spherical field: d orbitals degenerate spherical field free ion • What will happen when six ligands approach from the six vertices of an octahedron? • • • • •

  16. Crystal Field Theory t2g eg

  17. Crystal Field Theory t2g eg eg t2g crystal field stabilization energy (CFSE)

  18. Crystal Field Theory eg t2g crystal field stabilization energy (CFSE)

  19. Crystal Field Theory Distribution of electrons d2 d3 How is a d4 configuration distributed?

  20. Crystal Field Theory Pairing energy (P) vs. DO If DO < P, weak field; e.g., [Cr(OH2)6]2+ If DO > P, strong field; e.g., [Cr(CN)6]4–

  21. Crystal Field Theory Tetrahedral field t2 e t2 e

  22. Crystal Field Theory Square planar field DSP

  23. Crystal Field Theory Factors affecting magnitude of D Oxidation state of the metal ion Nature of the metal ion Number and geometry of the ligands Nature of the ligands

  24. Crystal Field Theory Ligands are point charges Metal d electrons repel ligands Splitting of d orbitals Explanation for colors and magnetism of complex ions No hybridization required

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