Successive crystalline-state photoisomerization of the 4-cyanobutyl group in a cobaloxime complex

The 4-cyanobutyl group bonded to the cobalt atom in a cobaloxime complex cr ystal was isomerized to the 2-cyanobutyl group through the 3-cyanobutyl gro up on exposure to a xenon lamp with retention of the single crystal form. T he X-ray crystal structure analysis of the initial crystal, (I), and the cr ystal after 66 hours exposure, (II), revealed that the produced 3-cyanobuty l group at one site in (II) is not disordered racemates but one enantiomer. The occupancy factors of the 4-cyanobutyl and the produced 3-cyanobutyl gr oup were 0.786(7) and 0.214(7), respectively in (II). Although the structur e of the produced 2-cyanobutyl group was not located on the difference elec tron density map, the NMR measurement clearly indicated that a small amount of the 2-cyanobutyl complex (ca. 6%) was produced.