CRYSTALLINE-STATE REACTION OF COBALOXIME COMPLEXES .18. METASTABLE INTERMEDIATE STRUCTURE OBSERVED BY A NEW X-RAY DIFFRACTOMETER FOR RAPID DATA-COLLECTION

A crystal of [(R)-1,2-bis(methoxycarbonyl)ethyl]bis(dimethylglyoximato)(diphenylmethylphosphine)-cobalt(III) changes its cell dimensions with retention of the single crystal form on exposure to visible light. The change is so fast that a new type of diffractometer (IPD-WAS) was developed for rapid data collection. The structures were analyzed at four different stages of the change using the diffractometer, which enabled us to collect the three-dimensional intensity data within 2 h. The cell dimensions of the monoclinic crystal varied from a=13.678(2), b=24.880(6), c=9.391(2) Angstrom, beta=107.99(1)degrees, and V=3040(1) Angstrom(3) to a=13.56(1), b=25.06(1), c=9.381(6) Angstrom, beta=107.35(6)degrees, and V=3044(3) Angstrom(3). The space group was changed from P2(1) to P2(1)/n. The structures at four stages showed that there are two crystallographically independent molecules, A and B, in an asymmetric unit of the crystal before irradiation and that the chiral 1,2-bis(methoxycarbonyl)ethyl (bmce) group of the B molecule is completely inverted to the opposite configuration while the chiral bmce group of the A molecule remains unaltered after irradiation. This brings about an inversion center between the two molecules. The reaction cavity for the B bmce group is significantly greater than that for the A bmce group. At the intermediate stages, the B bmce group takes complicated disordered structures, which indicates that there exists a metastable intermediate structure in the inversion process.