Spectroscopic Studies of Some Coordination Compounds

Abstract

In part one, spectroscopic methods are used in a study of the products of some metal-promoted reactions of 2-cyanopyridine. This compound reacts exothermically with copper(II) chloride in methanol to give dichlorobis/ 0-methylpyridine- -2-carboximidate /copper(II). Methyl 2-picolinate and pyridine-2-carboxamide may both be obtained in good yield via metal-promoted reactions of this type. Some proposed mechanisms for these reactions are discussed. Nine new complexes of O-methylpyridine-2-carboximidate are characterised by spectroscopic, magnetic, and conductimetric methods, Spectroscopic evidence for the electron-rich nature of this_ ligand is used in an explanation of its unusually high d-orbital splitting capacity. In part two, infrared and Raman data for triphenylamine, tri(2-pyridyl)amine, tri(2-pyridyl)phosphine and tri(2-pyridylarsine) are presented, and vibrational assignments are proposed. A literature survey focuses attention on inter-ring vibrational coupling in these molecules. In part three, assignments for metal-ligand vibrations in a closely related series of complexes of the type bis/ tri(2-pyridyl)amine 7M *2x~ are made by comparing infrared and Raman data obtained in both solid state and in solution. Most of the "ligand" vibrations of the centrosymmetric cations (Dag symmetry) are accidentally degenerate, but splittings are observed in the low-spin complexes. Variable temperature magnetic and spectroscopic studies of bis/ tri(2-pyridyl)- amine /cobalt(II) perchlorate show that an equilibrium between 4T and 2E spin states exists in this complex. The dependence of the susceptibility on the crystal structure in complexes of this type is attributed, in part, to variations in the abilities of different lattices to accommodate the predicted Jahn-Teller distortions in the low-spin isomers. Explanations are given for the unusually high Δ value produced by terdentate tri(2-pyridyl)amine, and for its tendency to form diacidobis(bidentate) complexes.