Quantitative comparison of photoisomerization of three cobaloxime complexes in the solid and crystalline states

Abstract

The β-cyanoethyl group bonded to the cobalt atom in cobaloxime complexes with 3-methyl-, 3-chloro- and 3-bromopyridines as axial base ligands was found, on exposure to a xenon lamp, to be isomerized to the α-cyanoethyl group with retention of the single-crystal form. The reaction rate of each compound was estimated from the change of unit-cell dimensions on a diffractometer (crystalline state) and from the change of the IR spectra of the powdered sample (the solid state). The reaction rates thus obtained were compared with the volumes of the reaction cavities for the cyanoethyl groups in the crystal structures of the three cobaloxime complexes. A quantitative relationship was observed between structure and reactivity.