Investigation of nitro-nitrito photoisomerization: Crystal structures of trans-{2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}(pyridine/4-methylpyridine)nitrocobalt(III)

The reaction cavities of the nitro groups in the title compounds, trans-{2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato-κ⁴ O,N,N′,O′}(nitro-κN)(pyridine-κN)cobalt(III), [Co(C₁₆H₁₄N₂O₂)(NO₂)(C₅H₅N)], (I), and trans-{2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato-κ⁴ O,N,N′,O′}(4-methylpyridine-κN)(nitro-κN)cobalt(III), [Co(C₁₆H₁₄N₂O₂)(NO₂)(C₆H₇N)], (II), have been investigated to reveal that the intermolecular CMe - H⋯O(nitro) contacts in (II) are unfeasible for the nitro-nitrito photochemical linkage isomerization process. In (I), there are two independent complexes showing similar conformations, and the central five-membered chelate ring of the tetradentate salen ligand adopts the same absolute configuration. This is the result of pseudo-spontaneous resolution, since the configuration of the five-membered chelate ring may frequently be reversed in solution. In the crystals of (I) and (II), the molecules are linked into three-dimensional networks by C - H⋯O hydrogen bonds.