The properties of transition-metal complexes of dipyrromethenes. Part I. The spectra and magnetic moments of some nickel(II) complexes

Abstract

Bis(dipyrromethenato)nickel(II) chelates with five 4,4′- and 5,5′- substituted dipyrromethenes have been prepared. Their magnetic moments and ligand-field spectra have been used to infer their stereochemistries in the solid state, in pyridine, and benzene solutions.

Each of the five complexes appears to be tetrahedral in benzene solution, irrespective of whether the 5,5′-positions of the ligand are occupied by methyl groups or not. Values for Δ, the ligand-field strength, and B′, the Racah inter-electronic repulsion integral, have been calculated from the benzene solution spectra and have been found to be markedly dependent on substitution at the 4,4′- and 5,5′-positions of the ligand. The complexes having methyl groups at both the 5- and 5′-positions remain tetrahedral in pyridine solutions but the complexes having a methyl group in only one of the 5,5′-positions, or in neither, add pyridine to form probably distorted octahedral complexes. In the solid state the complex without substituents in the 5,5′-positions may be closer to a planar configuration than the other four complexes which are effectively tetrahedral.