Some Cyclic Tetra-Amines and Their Metal Ion Complexes – a Synthetic and Structural Study

Abstract

This investigation is concerned with the preparation and properties of some cobalt(III) complexes of four isomeric cyclic tetra-amines, the preparation and Properties of some cobalt(II) complexes of one of the isomeric cyclic tetra-amines, and a three-dimensional structural analysis of a nickel(II) derivative of one of these cyclic tetra-amines. The isomeric cyclic tetra-amines teta tetb tetc, and tetd (all these amines are isomers of hexamethyl-1,4,8,11-tetra-azacyclotetradecane) are tetradentate ligands from which cobalt(III) complexes ,[Co(tet)X2]n+(where tet = teta tetb tetc or tetd and X = a monodentate ligand), can be prepared. A number of these derivatives [Co(tet)X2]n+, which are of interest in connection with the stereochemical consequences of substitution in octahedral complexes, have been isolated and characterised with respect to infrared and electronic spectra. In addition with the amines tetb and tetd, it was possible to prepare cis cobalt(III) derivatives [Co(tet)A]n+ (where tet = tetb or tetd and A = a chelated bidentate ligand). A number of these cis cobalt(III) derivatives have been prepared, including one containing a bidentate nitrate group co-ordinated to cobalt(III). A number of cobalt(II) complexes [Co(teta)X2] (where X = NO3-, Cl-, Br-, I-, NCS-, and BH4-), have been isolated and characterised. On the basis of infrared evidence, where applicable, and chemical evidence these derivatives are octahedral and the magnetic data indicate that they are “spin-paired”, having one unpaired electron. In addition, a pentaco-ordinate cobalt (II) derivative [Co(teta)Cl04]Cl04, having one ionic and one co-ordinated perchlorate group, has been isolated, and characterised by infrared and conductance data. A three dimensional X-ray structural determination of the crystal and molecular structure of the nickel(II) acetato-derivative [Ni (tetb)OAc] C104 has been attempted. This derivative is of cis configuration, and it contains a bidentate acetate group co-ordinated to the metal ion. The aim of this structural study was to establish the configuration of the amine ring in a complex of cis configuration, and this objective has been realised.