Investigation of solid-state photochemical nitro–nitrito linkage isomerization: crystal structures of trans-bis(ethylenediamine)(isothiocyanato)nitritocobalt(III) salts: thiocyanate, chloride monohydrate, and perchlorate–thiocyanate(0.75/0.25)

The reaction cavities of the nitro groups in the crystals of the title compounds, trans-[Co(NO2)(NCS)(C2H8N2)2]·X, X = SCN− (I), Cl−·H2O (II), and (ClO4−)0.75(SCN−)0.25 (III), have been investigated, revealing that the geometry of the intermolecular N—H...O hydrogen bonds in (I) is unsuitable for nitro–nitrito photo-isomerization. The common main building block of these crystal structures is a centrosymmetric pair of complex cations connected by pairwise N—H...O(nitro) hydrogen bonds forming an R22(4) ring, which is a narrow diamond shape in (I) but is approximately square in (II) and (III). The structure of (I) was reported earlier [Börtin (1976). Acta Chem. Scand. A, 30, 503–506] but is described here with an improved disorder model for the thiocyanate anions and to higher precision