Hydrogen Bond Network Accerelates Crystalline-State Photoisomerization of Cobaloxime Complexes. Akiko Sekine, Takayuki Yoshimiya and Yuji Ohashi Department of Chemistry, Faculty of Science, Tokyo Institute of Technology, Oookayama, Meguro-ku, Tokyo 152, Japan

Hydrogen bond network effectively keeps the crystal lattice and acceralate of reaction rate in the photoisomerization of the cobaloxime complexes, and the chirality of the product depends on the chiral environment around the reactive group.

It has been found that the achiral 2-cyanoethyl group bonded to the cobalt atom in the cobaloxime complex crystal with 3-methylpyridine as an axial base ligand was isomerized to the 1-cyanoethyl group on exposure to visible light with retaining single crystal form. Although the conversion rate was 55%, the produced 1-cyanoethyl group was not racemic, the R to S ratio being 4:7. In order to confirm such an asymmetric induction in a chiral crystal environment, another example with the higher conversion rate than that of the 3-methylpyridine complex has been sought, changing the axial base ligand. The single crystal of the N-(hydroxyethyl)-isonicotinamide complex was exposed to the xenon lamp and the crystal structure was determined after the irradiation. More than 70% of the complex was isomerized without degradation of the single crystal form. The OH group of the N-(hydroxyethyl)isonicotinamide ligand makes a hydrogen bond with the oxygen of the cobaloxime of the neighboring molecules and the two dimensional hydrogen bond network is formed in the crystal. The produced 1-cyanoethyl group has only one absolute configuration in one site of the crystal. The shape of the reaction cavity for the reaction group clearly explains the asymmetric induction.