COORDINATION COMPOUNDS COMPLEX By s. r. ratnam.

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COORDINATION COMPOUNDS COMPLEX

COORDINATION COMPOUNDSCOMPLEXBys. r. ratnam

Alfred WernerSwitzerlandUniversity of ZurichSwitzerlandb. 1866 d. 1919

Alfred Werner (1866-1919)1893, age 26: coordination theoryNobel prize for Chemistry, 1913Addition of 6 mol NH3 to CoCl3(aq)Conductivity studiesPrecipitation with AgNO34Werners explanation of coordination complexesMetal ions exhibit two kinds of valence: primary and secondary valencesThe 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 metalThe secondary valence is also termed the coordination number of the metal in a coordination complex5Werner Coordination TheoryCompoundMoles of ionsMoles of AgCl(s)CoCl3.6NH3CoCl3.5NH3CoCl3.4NH3CoCl3.3NH343320210

Cl attached to NH3 may be dissociatedWerner Coordination TheoryCompoundMoles of ionsMoles of AgCl(s)[Co(NH3)6]Cl3[Co(NH3)5Cl]Cl2[Co(NH3)4Cl2]Cl[Co(NH3)3Cl3]43320210Proposed six ammonia molecules to covalently bond to Co3+Coordination ChemistryDefinitionsCoordination 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 centerMiessler, Tarr, p. 278Coordination ChemistryDefinitionsCoordination compounds

3Cl

MligandN forms a coordinate covalent bond to the metal(coordination sphere)(counterion)9Coordinate covalent bond, hence coordination compoundsCoordination ChemistryDefinitionsLigands simple, complexDenticity different number of donor atomsChelates compounds formed when ligands are chelating (Gk. crabs claw)

Mbidentate

Valence Bond TheoryDeveloped by Linus PaulingOverlap of an empty orbital with a fully-filled orbital leads to the formation of a co-ordinate covalent bond or dative bondBonding in Coordination CompoundsValence Bond Theory

Tro, Chemistry: A Molecular Approach15Geometry of complexMagnetic properties of complexElectronic configuration of Metal ionNature of Bonding

VBT explainsVBT Valence Bond Theory

Tro, Chemistry: A Molecular Approach20Geometries in Complex Ions

tetrahedral

octahedral

Polydentate LigandsEthylenediaminetetraacetate, mercifully abbreviated EDTA, has six donor atoms.

Valence Bond TheoryMetal or metal ion: Lewis acidLigand: Lewis baseHybridization of s, p, d orbitalsC.N.Geometry4tetrahedral564Hybridssp3square planardsp2trigonal bipyramidaldsp3 or sp3doctahedrald2sp3 or sp3d2Valence Bond TheoryExample 1: [Co(NH3)6]3+Co [Ar] 3d7 4s2Co3+ [Ar] 3d63d4s4pif complex is diamagnetic4dd2sp3octahedral:Valence Bond TheoryExample 2: [CoF6]3Co [Ar] 3d7 4s2Co3+ [Ar] 3d6if complex is paramagnetic3d4s4p4d4sp3d2octahedralValence Bond TheoryExample 3: [PtCl4]2, diamagneticPt2+ [Xe] 4f14 5d85d6s6pdsp2square planarValence Bond TheoryExample 4: [NiCl4]2, tetrahedralNi2+ [Ar] 3d83d4s4p4sp3paramagneticValence Bond TheoryLigands (Lewis base) form coordinate covalent bonds with metal center (Lewis acid)Relationship between hybridization, geometry, and magnetismInadequate explanation for colors of complex ionse.g., [Cr(H2O)6]3+, [Cr(H2O)4Cl2]+

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