Crystalline-state reaction of cobaloxime complexes by X-ray exposure. 15. Different reactivity between two crystallographically independent molecules

Abstract

Introduction A new type of crystalline-state reaction has been found in [(R)-l-cyanoethyl]bis(dimethylglyoximato)(piperidine)cobalt(III) (dimethylglyoximato = 2,3butanedione dioximato). Crystal data at 293 K are as follows: [Co(C3H4N)(C4H7NzOz)2(CsH l iN)], M,=4284, a=11-733(2) , b=31-026(5 ) , c = 11.311(2)/k, V 4117(1)A 3, P2~2~2~, Z = 8 , Dx= 1.383 g cm3, F(000) = 2024, A(Mo Ka) = 0.79069/k, Iz = 8.06 c m ' . The final R value was 0.062 for 3573 reflections. The cell dimensions changed gradually on exposure to X-rays at 333 K, although the crystalline-state racemization was not observed at 293 K. Three-dimensional intensity data were collected in the early stages at 333 K (stage I). The cell dimensions before data collection were a = 11.788 (2), b = 31.146 (7), c = 11.359 (2)/k, V= 4170(1) A3; and after data collection were a11.779(2), b=31 .085(7 ) , c=11 .368(2 ) A, V= 4163 (1)/k 3. The average dimensions were used for the structure determination: a = 11.784(2), b = 31-112(7), c=11 .364 (2 )~ , , V = 4167 (1) ,~, 3. The structure analyses revealed that one cyanoethyl group of the two crystallographically independent molecules is disordered about the C o C bond. After 92 h X-ray exposure at 333 K three-dimensional intensity data were collected (stage II) since the changes in cell dimensions became sufficiently small. Average cell dimensions for stage II are a = 11.774(2), b = 31.043 (5), c = 11.379 (2)/k, V = 4159 (1)A3. With regard to the disordered cyanoethyl group, 24% was inverted, whereas another crystallographically independent cyanoethyl group remained unaltered. The difference in reactivity between the two groups is explained by the different cavity sizes for the two reactive groups. 0108-7681/91/050702-06503.00 It has been found that the chiral l-cyanoethyl (ce) group in crystals of some bis(dimethylglyoximato)cobalt (cobaloxime) complexes is racemized by X-ray exposure without degradation of the crystal (Ohashi & Sasada, 1977). The racemization processes observed in the related cobaloxime crystals are classified into three modes. In mode 1, the crystal has one molecule in the asymmetric unit and the disordered racemates appear after racemization (Ohashi, Yanagi, Kurihara, Sasada & Ohgo, 1981; Ohashi, Sasada & Ohgo, 1978a,b; Tamura, 1987). The crystals of modes II and III have two crystallographically independent molecules which a re related by a pseudoinversion center that becomes a crystallographic center after racemization. In this case the space group changes from chiral to centrosymmetric. In mode II the configuration of one of two crystallographically independent ce groups is fully inverted and the ordered chiral crystal is transformed to the ordered racemic one (Ohashi, Uchida, Sasada & Ohgo, 1983; Ohashi, Yanagi, Kurihara, Sasada & Ohgo, 1982; Uchida, Ohashi, Sasada, Ohgo & Baba, 1984). On the other hand, both of the crystallographically independent ce groups are converted to the disordered racemates in mode III (Tomotake, Uchida, Ohashi, Sasada, Ohgo & Baba, 1985). In the previous paper, we reported a new type of racemization which belonged to none of the above three classes (Ohashi, Tomotake, Uchida & Sasada, 1986). The crystal, in which the ligand 3-methylpyridine occupies an axial base position, R-ce-3mepy, contains two molecules, A and B, in the P212~2, cell. At an early stage both of the ce groups were inverted to give the disordered racemates, but the ce group of the A molecule, the A ce group, returned to the © 1991 International Union of Crystallography YASUKO T. OSANO et al. 703 original configuration after about 400 h exposure. Finally, the B ce group was fully inverted to the opposite configuration and the A ce group was transformed to the original one. The somewhat large size of the reaction cavity of the A c e group and the chiral space group after racemization may cause such differences in the racemization process. Recently, we prepared another crystal which had two independent molecules, A and B (space group P21212~), using piperidine as an axial base ligand (R-ce-pip). The racemization process, however, is somewhat different from that of R-ce-3mepy. The present paper reports the new type of racemization.