Acta Crystallographica Section B

Structural Science

Volume 56, Part 2 (April 2000)

research papers

Acta Cryst. (2000). B56, 245-253 [ doi:10.1107/S0108768199012008 ]

Direct observation of deuterium migration in crystalline-state reaction by single-crystal neutron diffraction. II. 3-1 Photoisomerization of a cobaloxime complex

T. Ohhara, J. Harada, Y. Ohashi, I. Tanaka, S. Kumazawa and N. Niimura

Abstract: Single crystal neutron diffraction analysis of photo-exposed(3-cyanopropyl-d₂^,)-[(R)-1-phenylethylamine-d₁₁]bis(dimethylglyoximato-d₁₄)cobalt(III) was carried out in order to clarify the mechanism of the crystalline-state photoisomerization of the 3-cyanopropyl group bonded to the Co atom in some cobaloxime complexes. Before irradiation the two H atoms bonded to the C¹ atom of the 3-cyanopropyl group were exchanged with the D atoms such as -CH₂CH₂CD₂CN. On exposure to a xenon lamp, the cell dimensions of the crystal were gradually changed. After 7 d exposure the change became insignificantly small. The structure was analyzed by neutron diffraction. The 3-cyanopropyl group was transformed to the 1-cyanopropyl group such as -CD(CN)C(H_1/2,D_1/2)₂CH₃ with retention of the single-crystal form. This indicates that one of the D atoms bonded to C¹ migrates to either position bonded to C². The other atoms of the complex remained unchanged. These results indicate that photoisomerization proceeded in two steps: the 3-cyanopropyl group was isomerized to the 2-cyanopropyl group in the first place and then the 2-cyanopropyl group was transformed to the 1-cyanopropyl group. Moreover, it was made clear that the second-step isomerization was irreversible, since one of the D atoms was retained. The disordered structure at C² is estimated to be caused by the interconversion between the 1-cyanopropyl group produced and its dehydrogenated olefin after the photoisomerization.

Keywords: Deuterium migration; Neutron diffraction; Photoisomerization; Cobaloxime.


	Structure factor file (CIF format) (346.3 kbytes) Contains datablock 1bXin

	Structure factor file (CIF format) (325.4 kbytes) Contains datablock 1bXirr

	Structure factor file (CIF format) (74.2 kbytes) Contains datablock 1bNirr

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