Acta Crystallographica Section B

Structural Science

Volume 57, Part 4 (August 2001)

Acta Cryst. (2001). B57, 551-559 [doi:10.1107/S0108768101006838]

Direct observation of deuterium migration in crystalline-state reaction by single-crystal neutron diffraction. III. Photoracemization of 1-cyanoethyl cobaloxime complexes

T. Ohhara, H. Uekusa, Y. Ohashi, I. Tanaka, S. Kumazawa and N. Niimura

Abstract: The H atoms bonded to the chiral C atoms (stereogenic center) of the 1-cyanoethyl groups in two cobalt complexes, [(R)-1-cyanoethyl]bis(dimethylglyoximato)(pyridine)cobalt(III) (2) and [(R,S)-1-cyanoethyl]bis(dimethylglyoximato)(piperidine)cobalt(III) (3), were replaced with D atoms, such as Co-C*D(CH₃)CN. The crystals of the two cobalt complexes were irradiated with a xenon lamp for 72 h and 27 d, respectively. The unit-cell dimensions were gradually changed with retention of the single-crystal form. The crystal structures after irradiation were determined by neutron diffraction. In each crystal the chiral 1-cyanoethyl group of one of the two crystallographically independent molecules was partly inverted to the opposite configuration, whereas that of the other molecule kept the original configuration. The C*-D bond in the inverted group was completely conserved in the process of the inversion of the chiral alkyl group. This suggests that the inversion of the chiral 1-cyanoethyl group proceeds with the rotation of the cyanoethyl radical after the Co-C bond cleavage by photo-irradiation so that the opposite side of the radical faces the Co atom. This is followed by recombination of the Co-C bond to form the inverted 1-cyanoethyl group.

Online 24 July 2001


	Structure factor file (CIF format) (222.5 kbytes) Contains datablock 2-initial

	Structure factor file (CIF format) (419.7 kbytes) Contains datablock 2-irradiated

	Structure factor file (CIF format) (70.0 kbytes) Contains datablock 2-neutron

	Structure factor file (CIF format) (404.3 kbytes) Contains datablock 3-initial

	Structure factor file (CIF format) (880.3 kbytes) Contains datablock 3-irradiated

	Structure factor file (CIF format) (105.1 kbytes) Contains datablock 3-neutron

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