Metal complexes as ligands. VII. Copper bromide complexes with bidentate schiff bases

Abstract

A series of new binuclear copper(II) complexes has been prepared by the reaction of copper(II) bromide with bis(N-R-salicylaldimino) copper(II) complexes, where R is a normal or branched alkyl, or a phenyl group. The room temperature magnetic moments are considerably below the «spin-only» values, due to antiferromagnetic exchange interactions between adjacent copper atoms. The ligand field absorption spectra are in keeping with only one type of copper atom, indicating that the environment about each of the two copper atoms is the same. These properties are explained in terms of a trans structure ▪ for these binuclear complexes derived from bidentate salicylaldimines, as opposed to the cis structure for the analogous derivatives of tetradentate salicylaldimines. This trans structure is analogous to that proposed earlier for copper chloride complexes with bidentate Schiff Bases. The magnetic moments and the ligand field absorption spectra are not very sensitive to the size of the R- group on the nitrogen, indicating that the steric effect of these groups is fairly small, as expected for the proposed structure. The copper bromide complexes are less stable, and lower melting, than the chloride complexes. The ligand field absorption bands are at lower energies in the bromide than in the chloride complexes; this is interpreted in terms of a difference in ligand field strength as well in stereochemistry.