Syntheses, structures and properties of trans-dichlororuthenium(II) complexes with N < inf > 4 < /inf > -donor Schiff bases

Abstract

The reactions of hydrated RuCl3 and tetradentate Schiff bases (L = paen, papn and pabn) derived from 2-pyridine-carboxaldehyde and linear diamines such as 1,2-diaminoethane, 1,3-diaminopropane and 1,4-diaminobutane in boiling methanol afford complexes of general formula trans-[RuLCl2]. The complexes were characterised by analytical, spectroscopic and electrochemical data. All the complexes are diamagnetic and electrically non-conducting. Thus in each complex the metal ion is in +2 oxidation state. The molecular structures of trans-[Ru(papn)Cl2] and trans-[Ru(pabn)Cl2] in the solid state have been determined by X-ray crystallography. In each molecule, the ruthenium(II) centre is in distorted octahedral N4Cl2 coordination sphere. The neutral ligand coordinates via two pyridine-N and two imine-N atoms forming a N4 square-plane around the metal ion. The chloride ions satisfy the remaining two trans sites. The proton NMR spectra of all the complexes in CDC13 solutions are consistent with the trans arrangement of the chloride ions. Electronic spectra of the complexes in dichloromethane solutions display intense metal-to-ligand charge transfer bands in the range 595-656 nm. Cyclic voltammograms of the complexes in acetonitrile solutions display a reversible oxidation response in the potential range 0.26-0.40 V (vs. saturated calomel reference electrode) due to RuIII/RuII couple. © 2003 Elsevier Science Ltd. All rights reserved.