Polynuclear chromium(III) complexes with bromide bridging. Thermal and magnetic studies

Abstract

Two new polynuclear chromium(III) complexes with a bromide bridge have been prepared and characterized. One of them is a dinuclear with two Br − as a bridging ligand; the other is presumably an angular trinuclear with only one Br − as a bridgin ligand between each pair of Cr(III) ions. The complexes were prepared by heating in the solid state the known precursor complexes [CrF 2(aa)(H 20) 2] Br (aa=ethylenediamine or 1,2-cyclohexanediamine). By means of TG measurements the kinetic parameters have been calculated for the two processes. The activation energy, E a, is very low in both cases indicating a dissociative mechanism and an open structure in the crystal lattice. The magnetic measurements up to helium liquid temperature indicate a weak antiferromagnetic coupling constant in the trinuclear complex of ethylenediamine hut a Curie law behaviour in the dinuclear compound of 1,2-cyclohexanediamine.