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(NO 2)(NCS)(C 2 H 8 N 2) 2 ]·X, X = SCN - (I), Cl - ·H 2 O (II), and (ClO 4 -) 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 R 2 2 (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.