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.