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-kappa O-2,O')(nitro)(pyridine-kappa N)cobalt(III), [Co(C5H7O2)(2)(NO2)(C5H5N)], (I), trans-bis(acetylacetonato-kappa O-2,O')(4-methylpyridine-kappa N)(nitro)cobalt(III), [Co(C5H7O2)(2)(NO2)(C6H7N)], (II), and trans-bis(acetylacetonato-kappa 2O,O')(3-hydroxypyridine-kappa N)(nitro)cobalt(III) monohydrate, [Co(C5H7O2)(2)(NO2)(C5H5NO)]center dot H2O, (III), have been investigated to reveal that bifurcated intermolecular C(py)-H center dot center dot center dot 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 center dot center dot center dot O hydrogen bonds, whereas the extended structure of (III) features (010) layers linked by O-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds. Compounds (I) and (II) were refined as inversion twins.