Studies in co-ordination chemistry

Abstract

Several theories have been put forward to explain the unique physical and chemical properties of the transition metal elements in terms of their electronic configuration, co-ordination ability and bonding. The best known of these are Pauling's Valence bond, Crystal Field, Molecular Orbital and Ligand Field Theories. The theory which at present has the most general application is the Ligand Field Theory Moffit and BaLLhausen: Ann.Rev.Phys.Chem.1956, 7, 107., Report to the 10th Solvay Council, Brussels 1956, 225, 289 and 355., Griffith and Orgel Quart.Revs. 1957, 11, 381. which is a combination of the Crystal Field Theory and Molecular Orbital Theory. Pauling's Theory Pauling, L. J.Amer.Chem.Soc. 1931, 53, 1367; 1932, 54, 994 J.Chem.Soc. 1948 1641. Pauling,L. and Wilson,E.B.: Introduction to Quantum Mechanics 1935. New York: McGraw-Hill. Huggins.J.; Chem.Phys.1937, 5, 527. Taube: Chem.Revs.1952, 50, 69. fails to explain several properties of the transition metal co-ordination compounds. Among these are the visible absorption spectra and hence it is of little importance to this thesis. Crystal Field Theory Moffit and Ballhausen: Ann.Rev.Phys.Chem.1956, 7, 107. Griffith and Orgel Quart.Revs. 1957, 11, 381. Pearson.R.G.: Chem.Eng News 1959, 37, No.26, 72 The essence of this theory is that the five d orbitals which are degenerate in the gaseuos metal ion are differentiated by the electrostatic field created by the presence of the ligands. Covalent bonding is neglected, the compound being considered as held together by electrostatic forces. The orbitals penetrating closer to the ligands are raised in energy compared with those relatively further from the ligand. The pattern of splitting depends on the number and arrangement of the ligands. See Figure 1.