Comparative crystal structure studies on distortion of iso-butyl(aqua)cobaloxime induced by alpha-cyclodextrin and beta-cyclodextrin hosts

The crystal and molecular structures of isa-butyl(aqua)cobaloxime (I) and i ts hydrated inclusion complexes with alpha-cyclodextrin (II) and beta-cyclo dextrin (III) were determined by X-ray diffraction analyses. Crystal data f or I: P2(1)/c, a = 30.450(1) Angstrom; b = 9.659(2) Angstrom; c = 19.200(2) Angstrom; beta = 107.23(3)degrees; Z = 12. Crystals of II . H2O and III . 9H(2)O both crystallize in space group P2(1)2(1)2(1) With Z = 4; a = 13.847 (1) Angstrom, b = 19.418(1) Angstrom, c = 24.593(1) Angstrom for II . 8H(2) O, and a = 28.188(6) Angstrom, b = 15.190(3) Angstrom, c = 19.017(4) Angstr om for III . 9H(2)O. In the inclusion complexes, the Co(DH)(2) unit is loca ted near the wide opening of the cyclodextrin with its iso-butyl group inse rted into the cyclodextrin cavity. The structure and conformation changes o f the iso-butyl(aqua)cobaloxime are probably related to the noncovalent int eraction between the iso-butyl group and cyclodextrin cavity, and steric in teraction between cobaloxime and cyclodextrin rims. Our results also show t hat distortions of iso-butyl(aqua)cobaloxime/cyclodextrin induced by alpha- CD and beta-CD occur in different extent, which assumedly is due to the dif ferent cavity diameters of the cyclodextrins.