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-κ2O,O′)(nitro)(pyridine-κN)cobalt(III), [Co(C5H7O2)2(NO2)(C5H5N)], (I), trans-bis(acetylacetonato-κ2O,O′)(4-methylpyridine-κN)(nitro)cobalt(III), [Co(C5H7O2)2(NO2)(C6H7N)], (II), and trans-bis(acetylacetonato-κ2O,O′)(3-hydroxypyridine-κN)(nitro)cobalt(III) monohydrate, [Co(C5H7O2)2(NO2)(C5H5NO)]·H2O, (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