Influence of co-ligands in synthesis, photoluminescence behavior and catalytic activities of zinc complexes of 2-((E)-((pyridin-2-yl)methylimino)methyl)phenol

Abstract

Four new zinc(II) complexes of a tridentate Schiff base ligand 2-((E)-((pyridin-2-yl)methylimino)methyl)phenol (HL), namely [Zn2L2Cl2] (1); [Zn2L2Br2] (2); [ZnL(SCN)(MeOH)] (3) and [Zn2L(OAc)3(MeOH)] (4) have been synthesized with the view to investigate the role of co-ligands in controlling the structural diversity, photoluminescence property and catalytic activities. The complexes have been characterized through common physicochemical techniques as well as by X-ray single crystal structural analysis. All of them display interesting co-ligands mediated photoluminescence property the origin of which may be attributed due to ligand to metal charge transfer (LMCT) and the order of photoluminescence efficiency is 3>4>1∼2. Catecholase and phosphatase activities of the complexes have been investigated in DMF medium using 3,5-di-tert-butylcatechol (3,5-DTBC) and 4-nitrophenylphosphate as substrates respectively. Co-ligands have prominent role on phosphatase activity of the complexes where the order of activity in terms of kcat value is 4>1>2>3. Interestingly, only complex 4 is active in catalyzing the aerobic oxidation of 3,5-DTBC. The presence of readily labile solvent molecule in one of the zinc centers of complex 4 perhaps takes the key role for initiating substrate-Zn interaction and thereby the activity. Radical pathway is the probable reason behind the catecholase activity as is evident from EPR study. Solid state thermal analysis suggests that ZnO is the thermally stable end product for complexes 1, 2 and 4, whereas it is ZnS in case of complex 3.