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COORDINATION COMPOUNDS COMPLEX

COORDINATION COMPOUNDS COMPLEX. By s. r. ratnam. Alfred Werner Switzerland University of Zurich Switzerland b. 1866 d. 1919. Alfred Werner (1866-1919) 1893, age 26: coordination theory Nobel prize for Chemistry, 1913 Addition of 6 mol NH 3 to CoCl 3 ( aq )

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COORDINATION COMPOUNDS COMPLEX

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  1. COORDINATION COMPOUNDSCOMPLEX By s. r. ratnam

  2. Alfred Werner Switzerland University of Zurich Switzerland b. 1866 d. 1919 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

  3. Werner’s explanation of coordination complexes Metal ions exhibit two kinds of valence: primary and secondary valences The primary valence is the oxidation number (positive charge) of the metal (usually 2+ or 3+) The secondary valence is the number of atoms that are directly bonded (coordinated) to the metal The secondary valence is also termed the “coordination number” of the metal in a coordination complex

  4. 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

  5. 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

  6. 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

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

  8. 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

  9. Valence Bond Theory Developed by Linus Pauling

  10. Bonding in Coordination CompoundsValence Bond Theory Overlap of anempty orbitalwith afully-filled orbitalleads to the formation of aco-ordinate covalent bondordative bond

  11. VBT explains • Geometry of complex • Magnetic properties of complex • Electronic configuration of Metal ion • Nature of Bonding Tro, Chemistry: A Molecular Approach

  12. VBT Valence Bond Theory

  13. Geometries in Complex Ions Tro, Chemistry: A Molecular Approach

  14. tetrahedral

  15. octahedral

  16. Polydentate Ligands Ethylenediaminetetraacetate, mercifully abbreviated EDTA, has six donor atoms.

  17. 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

  18. 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

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

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

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

  22. 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]+

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