Investigation of nitro–nitrito photoisomerization: crystal structures of trans-bis­(acetyl­acetonato-O,O′)(pyridine/4-methyl­pyridine/3-hy­droxy­pridine)nitro­cobalt(III)

The reaction cavities of the nitro groups in the title compounds, trans-bis­(acetyl­acetonato-κ(2) O,O′)(nitro)(pyridine-κN)cobalt(III), [Co(C(5)H(7)O(2))(2)(NO(2))(C(5)H(5)N)], (I), trans-bis­(acetyl­acetonato-κ(2) O,O′)(4-methyl­pyridine-κN)(nitro)cobalt(III), [Co(C(5)H(7)O(2))(2)(NO(2))(C(6)H(7)N)], (II), and trans-bis­(acetyl­acetonato-κ(2) O,O′)(3-hy­droxy­pyridine-κN)(nitro)cobalt(III) monohydrate, [Co(C(5)H(7)O(2))(2)(NO(2))(C(5)H(5)NO)]·H(2)O, (III), have been investigated to reveal that bifurcated inter­molecular C(py)—H⋯O,O contacts in (III) are unfeasible for the nitro–nitrito photochemical linkage isomerization process. In each structure, the pyridine ring and the Co atom lie on a crystallographic mirror plane; in (I) and (II) the nitro group lies in the same plane, whereas in (III), which crystallizes as a monohydrate, the nitro group is disordered over three orientations in a 0.672 (16):0.164 (8):0.164 (8) ratio; the water mol­ecule of crystallization is statistically disordered over two sites adjacent to the mirror plane. In the crystals of (I) and (II), the mol­ecules are linked into [100] chains by C—H⋯O hydrogen bonds, whereas the extended structure of (III) features (010) layers linked by O—H⋯O and C—H⋯O hydrogen bonds. Compounds (I) and (II) were refined as inversion twins.