4 POLYMORPHS OF A COBALOXIME COMPLEX WITH DIFFERENT SOLID-STATE PHOTOISOMERIZATION RATES

The complex )bis(dimethylglyoximato)(triphenylphosphine)cobalt (III) [ Co(C4H7N2O2)(2)(C3H4N){P(C6H5)(3)}], when it was crystallized rapidly from an aqueous methanol solution, has four crystal forms, three of wh ich were obtained separately from different solvents in large amounts. The crystal structures of the four forms were determined by X-rays. T he molecular structures in the four forms have different conformations around the Co-C and Co-P bonds. The packing energy calculation indica ted that the four forms have approximately the same energy. The 2-cyan oethyl group of this complex was isomerized to the 2-cyanoethyl group when the powdered sample of the complex was irradiated with a xenon la mp. For three crystal forms prepared separately, the solid-state photo isomerization rates were measured from the change in the IR spectra, a ssuming first-order kinetics. A quantitative relationship between the rate constant and the size of the reaction cavity for the 2-cyanoethyl group has been obtained for the three crystal forms.