Spectral and thermal studies of solid-phase thermochromism of Co(II) double metal complexes

Abstract

Tetrahedral solid state structures of the blue potassium tris(aryloxo)cobaltate(II)-tetrahydrofurane complexes of the formula KCo(OAr) 3·2thf (OAr = o-chloro-, o-bromo-, m-chloro-, p-bromo, 2,6-dichloro-, 2,4-dichloro- or 2,4-dimethylphenoxide) undergo solid-phase thermal tetrahedral to octahedral transformation accompanied by change in their colours from blue to rose (one-step thermochromism). Magnetic moments, electronic and infrared spectral studies supported these results. Thermal treatment of theses complexes leads to the loss of the crystallized thf molecule yielding also blue tetrahedral complexes. However, further heating leads to the loss of the coordinated thf molecule and the formation of rose octahedral trimeric products. TG-DTA results showed that the, two solvated thf molecules were eliminated in two steps. Mass spectral studies and IR intensity measurements confirmed the trimeric behaviour of the rose octahedral geometry of thermal products. Conductance measurements of solutions of these complexes in thf indicated that they behave as non-electrolytes.