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-κ² O,O′)(nitro)(pyridine-κN)cobalt(III), [Co(C₅H₇O₂)₂(NO₂)(C₅H₅N)], (I), trans-bis(acetylacetonato-κ² O,O′)(4-methylpyridine-κN)(nitro)cobalt(III), [Co(C₅H₇O₂)₂(NO₂)(C₆H₇N)], (II), and trans-bis(acetylacetonato-κ² O,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.