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

Abstract

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.