Abstract
The synthesis of some conjugated 1:3 di-imine Schiff's base ligand hydrochlorides, together with an investigation into their behaviour as ligands in acidic and basic media, is described. The conformation of some of the ligands has been investigated by means of comparisons between calculated electronic spectra, based upon an assumed geometry, and the observed spectra. The microsymmetry of the metal environments in the first-row transition metal complexes cannot be unambiguously deduced from the electronic spectra and room temperature, solid state, magnetic moments. Of principal interest are the isotropic proton resonance shifts of the bis (iminato) cobalt (II) and nickel (II) complexes. These are interpreted in terms of a dominant contact shift interaction stemming from partial delocalisation of an electron of B-spin from the highest filled bonding pi molecular ethital into metal 3d-atomic orbitals of appropriate symmetry. Evidence for concurrent delocalisation involving the ligand 6-bond system, rotation of the phenyl groups, unusual proton spin-spin relaxation effects, attenuation of spin density into the second ring of a biphenyl unit, and the presence of the pseudocontact interaction in the cobalt (II) complexes, is also presented. The literature appertaining to isotropic proton resonance shifts of complexes of divalent nickel and cobalt is reviewed.