NITRITO-NITRO LINKAGE ISOMERIZATION IN THE SOLID-STATE .1. X-RAY CRYSTALLOGRAPHIC STUDIES OF TRANS-BIS(ETHYLENEDIAMINE)(ISOTHIOCYANATO)NITRITOCOBOLT(III) AND TRANS-BIS(ETHYLENEDIAMINE)(ISOTHIOCYANATO)NITROCOBALT(III) PERCHLORATE AND IODIDE

The nitrito-nitro isomerization in the solid state has been investigated by. X-ray structure determinations of the perchlorate and iodide salts of ;ra/!5-bis(ethylenediamine)(isothiocyanato)nitritocobalt(III), trans-[Co(en)2(NCS)(ONO)]X, X- = ClO4-and I-, and the corresponding nitro complexes. The intensity data refined by collected at 245 K (for the iodide compounds) or at 165 K or 163 K (for the perchlorate compounds) by use of a computer-controlled four-circle diffractometer. All compounds are monoclinic, space group P21 with Z = 2. The structures were refined by using full-matrix least-squares methods. In the final models, the scale factor, the positional parameters, and the anisotropic thermal parameters on all nonhydrogen atoms were refined to an R value based on Fo equal to 0.054 and 0.049, respectively, for the nitrito and nitro iodides and to 0.081 and 0.103, respectively, for the corresponding perchlorates. Each structure contains mononuclear cationic cobalt complexes and perchlorate or iodide counterions. The coordination around cobalt is close to Oh, and, apart from the way of bonding of the ambidentate NO2- group, the structures are essentially identical. The structures of the two isomers indicate that the isomerization is intramolecular and that the reaction takes place in a plane by rotation of the NO2- group, most likely via a seven-coordinate transition state. The thermal isomerization of the perchlorate compound and the photochemical isomerization of the nitro perchlorate compound to the corresponding nitrito compound were both investigated by powder X-ray diffractometry. Both isomerizations proceed via the formation of a solid solution. The photochemically obtained nitrito compound gave a diffraction pattern identical with that of the original nitrito compound. Hence, the photochemical nitro → nitrito reaction also seems to take place by a rotation of the NO2- group. © 1979, American Chemical Society. All rights reserved.