A. Uchida

Crystalline-State racemization of a chiral cyanoethyl group connected by a hydrogen bond

The crystal of [(R)-1-cyanoethyl]bis(dimethylglyoximato)(pyrrolidine)cobalt(III) (dimethylglyoximato=2,3-butanedione dioximato) revealed a gradual change of cell parameters keeping the single-crystal form when it was irradiated by X-rays. It contains one water molecule as solvent in the asymmetric unit. The reactive cyanoethyl group is hydrogen bonded to the water molecule. In spite of the restriction by the hydrogen bond, the ordered chiral cyanoethyl group is converted to disordered racemates without degradation of crystallinity

β–α Photoisomerization of cobaloxime complexes in the solid state. I. Different reaction rates in polymorphic crystals

Two crystalline forms of (/3-cyanoethyl)bis (dimethylglyoximato) (3-methylpyridine) cobalt(I I I) (dimethylglyoximato =2,3-butanedione dioximato), C 17H25Co N604, [Co(C3H4N)(C4H7N202)2(C6H7N)], were obtained from methanol solutions. Form I: Mr = 436.36, monoclinic, P2Ja, a=23.742 (5), b= 9.496(2), c= 8.819 (1) ~, /3=94.59(2) °, V= 1981.9 (6)/~k3, Z = 4, Dx = 1.463 g cm-3,)t (Mo Ka) = 0.71069A, /z=8.42 cm i, F(000)=912, T=298 K, R=0.057 for 3955 observed reflections; form II: monoclinic, P21/a, a = 21.425 (4), b =9.290 (1), c = 11.517 (2) A, /3 =117.58 (2) °, V=2031.6(7)A3, Z= 4, Dx=l.427gcm -3, A (MoKa)=0.71069~, /~= 8.22 cm -~, F(000) -- 912, T = 298 K, R = 0.048 for 4198 observed reflections. The rate of/3-a isomerization for form II was much greater than that for form I. The structure analysis has shown that the conformations of the /3-cyanoethyl groups in forms I and II are almost the same and that there is greater room around the cyanoethyl group in form II than in form I.

Three polymorphs of (rac-1-cyanoethyl)(pyrrolidine)cobaloxime

Three crystal forms were found for (rac-1-cyanoethyl)bis(2,3-butanedione dioximato)(pyrrolidine)cobalt(III). Two forms, (I) and (II), were grown from solutions of aqueous methanol and benzene-chloroform, respectively, and the third, (III), was obtained by crystalline-state racemization [Takenaka, Ohashi, Tamura, Uchida, Sasada, Ohgo & Baba (1993). Acta Cryst. B49, 272-277]. The structures of (I) and (II) have been determined. (I): [Co(C 3 H 4 N)(C 4 H 9 N)(C 4 H 7 N 2 O 2 ) 2 ], triclinic, P1, Z= 4, a=11.723 (2), b=15.658 (3), c=11.118 (2) A, α=98.71 (2), β=90.17 (4), γ=98.52 (3) o , V= 1994.2 (8) A 3 , R=0.065, wR=0.079, M r =414.4, D m =1.39, D x =1.38 Mg m -3 , μ(Mo Kα)= 0.887 mm -1 , F(000)=872, T=296 K. (II): [Co(C 3 H 4 N)(C 4 H 9 N)(C 4 H 7 N 2 O 2 ) 2 ].3/2C 6 H 6 , monoclinic, P2 1 /a, Z= 4, a=16.621 (2), b=18.803 (2), c=9.155 (1) A, β=105.03 (2), V=2763.4 (7) A 3 , R=0.085, wR=0.105, M r =531.6, D x =1.28 Mg m -3 , μ(Mo Kα)= 0.655 mm -1 , F(000)=1124, T=296 K

Metal-semiconductor transition in (BEDT-TTF)3(ClO4)2

Abstract A metal-semiconductor transitio at T c =170.5K in a two-dimensional organic metal, (BEDT-TTF) 3 (ClO 4 ) 2 , was investigated by means of ESR, resistivities, specific heats and X-ray diffractions. The specific heats show a λ-type anomaly with a second order nature and a large entropy change ranging 3J/K.mol. In addition to the H/D isotope effects on T c , X-ray diffraction suggests the development of the hydrogen-bonding network between ethylene groups of BEDT-TTF molecules and ClO 4 anions T C . These experimental findings demonstrate that the metal-semiconductor transition is motivated by the three dimensional structural deformation which is closely correlated to the hydrogen bonding network.

Calculated Reaction Paths for a Solid-state Reaction: Racemization of Chiral Crystalline Cobaloxime Complexes by Exposure to X-Rays

Abstract By means of point-to-point calculation of the packing potential energy (PPE), reaction paths and differences in activation energies were obtained for the racemization of chiral cyanoethyl groups in crystalline cobaloxime complexes. The results of the calculations are generally compatible with the experimental results and throw some light on the details of the reaction paths.