Methylene bridge regulated geometrical preferences of ligands in cobalt(III) coordination chemistry and phenoxazinone synthase mimicking activity.

Two new azide bound cobalt(III) complexes, [Co(L(1))(N3)3] (fac-1) and [Co(L(2))(N3)3] (mer-2), where L(1) is bis(2-pyridylmethyl)amine and L(2) is (2-pyridylmethyl)(2-pyridylethyl)amine, derived from tridentate reduced Schiff-base ligands have been reported. Interestingly, a methylene bridge regulated preferential coordination mode of ligands is noticed in their crystal structures: it is found in a facial arrangement in fac-1 and has a meridional disposition in mer-2. Both complexes show phenoxazinone synthase-like activity and the role of the structural factor on the catalytic activity is also explored. Moreover, the easily reducible cobalt(III) center in mer-2 favors the oxidation of o-aminophenol. The ESI-MS positive spectra together with UV-vis spectroscopy clearly suggest the formation of a catalyst-substrate adduct by substitution of the coordinated azide ions in the catalytic cycle.