Bio-relevant manganese(II) compartmental ligand complexes: Syntheses, crystal structures and studies of catalytic activities

Abstract

Three new mono-manganese(II) complexes of a compartmental ligand, namely [Mn(HL)(H 2O) 3](NO 3) 2·H 2O ( 1), [Mn(HL)(SCN) 2(H 2O)]·H 2O ( 2), and [Mn(HL){N(CN) 2}(H 2O) 2](NO 3)·H 2O ( 3), where L = 2,6-bis{2-(N-ethyl)pyridineiminomethyl}-4-methylphenolato, have been synthesized and characterised by routine physicochemical techniques and complexes 1, 2 also by X-ray single crystal structure analysis. All the mono nuclear complexes contain Mn II high spin species at octahedral core as evidenced by magnetic moment (measured at 300 K) and EPR study at 77 K. As revealed by crystal structure analyses, the protonation of one imine nitrogen atom of the potential dinucleating ligand L hampers to form the expected dinuclear Mn II complex. However, complexes 1– 3 show excellent catecholase-like activity with both 3,5-di- tert-butylcatechol and tetrachlorocatechol as substrates. In addition complexes 1 and 2 also exhibit phosphatase activity, while 3 forms an adduct with p-nitrophenyl phosphate as substrate. To the best of our knowledge this is the first report of Mn II complexes being able to catalyze the oxidation of TCC to TCQ. Catecholase and phosphatase activities have been monitored by UV–vis spectrophotometer and Michaelis–Menten equation has been applied to rationalize all the kinetic parameters where complex 1 shows maximum k cat value followed by 2 and 3 (where for phosphatase activity 3 only forms an adduct).