Zinc(II) complexes of xylyl bridged bis(1,4,7-triazacyclononane) derivatives

Abstract

The xylyl bridged bis(tacn) ligands, T 2- o-X (1,2-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene) and T 2- p-X (1,4-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene) have yielded one mononuclear, [Zn(T 2- o-X)](ClO 4) 2 ( 1), and one dinuclear complex [Zn 2(T 2- p-X)(H 2O) 4(DMF) 2][ZnCl 4] 2 ( 2). A single-crystal X-ray structure determination of 1 has established that T 2- o-X ligand sandwiches a single zinc(II) centre, which adopts a distorted octahedral geometry. A structural analysis of 2 confirmed the formation of a binuclear [Zn 2(T 2- p-X)(H 2O) 4(DMF) 2] 4+ complex in which each zinc centre binds to one of the macrocyclic compartments of the T 2- p-X ligand and the remaining zinc coordination sites are occupied by water and DMF ligands. The coordination of DMF highlights the ability of carbonyl groups in amide molecules to bind to zinc(II), a feature of zinc enzymes that catalyse the hydrolysis of amide bonds in proteins (peptidases). A synthetic procedure has been developed which enables single pendant carboxymethyl groups to be attached to T 2- o-X and T 2- m-X. These bis(tetradentate) ligands form dinuclear zinc(II) complexes [Zn 2(T 2- o-X Ac 2)(H 2O) 4](ClO 4) 2·2H 2O ( 3) and [Zn 2(T 2- m-X Ac 2)(H 2O) 4](ClO 4) 2·2H 2O ( 4), whose structure has been probed by spectroscopic methods.