Investigation of nitro-nitrito photoisomerization: crystal structures of trans-bis-(acetyl-acetonato-O,O')(pyridine/4-methyl-pyridine/3-hy-droxy-pridine)nitro-cobalt(III).

The reaction cavities of the nitro groups in the title compounds, trans-bis-(acetyl-acetonato-κ2 O,O')(nitro)(pyridine-κN)cobalt(III), [Co(C5H7O2)2(NO2)(C5H5N)], (I), trans-bis-(acetyl-acetonato-κ2 O,O')(4-methyl-pyridine-κN)(nitro)cobalt(III), [Co(C5H7O2)2(NO2)(C6H7N)], (II), and trans-bis-(acetyl-acetonato-κ2 O,O')(3-hy-droxy-pyridine-κN)(nitro)cobalt(III) monohydrate, [Co(C5H7O2)2(NO2)(C5H5NO)]·H2O, (III), have been investigated to reveal that bifurcated inter-molecular 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 mol-ecule of crystallization is statistically disordered over two sites adjacent to the mirror plane. In the crystals of (I) and (II), the mol-ecules 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.