Ultraviolet spectral studies on metal biguanide complexes

Abstract

An attempt has been made to explain the shift of the u.v. spectra on the basis of a new metal biguanide complex structure taking into account the delocalised π-electron system in the ligand. The energy levels of biguanide have been calculated by a simple LCAO–MO method, and the perturbation of those energy levels by metal d orbitals has been schematically formulated by use of Dewar's perturbation method in order to understand qualitatively the direction of the shift. It is found that in planar complexes the energy of the d_xz and d_yz orbitals should be higher than that of the highest filled ligand orbital. It is suspected that there is more than one transition in the region under investigation. Because of the considerable uncertainty in the value of the various parameters, no attempt has been made to make a rigorous numerical fitting. The suggested structure of metal biguanide complexes indicates the possibility of additional ligand → metal interaction and thus explains the preferential tendency of biguanide for stabilising higher oxidation states of the metal.