Dinickel Complexes Bridged by Unusual (N,O,O )-Coordinated α-Amino Acids: Syntheses, Structural Characterization and Magnetic Properties

Abstract

Four novel dinickel complexes, coordinated by mixed ligands of tren and racemic amino acids, namely [Ni2(tren)2(dl-alaninato)(H2O)]I3·2H2O (1), [Ni2(tren)2(dl-leucinato)(H2O)]I3·2.5H2O (2), [Ni2(tren)2(dl-phenylalaninato)(H2O)]I3·H2O (3), and {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}n(4), have been synthesized and structurally characterized by X-ray crystallography, FTIR, u.v. and e.s. spectra. They represent the first series of dinickel(II) complexes bridged by the unusual (N,O,O′)-coordinated α-amino acids. In complexes (1–3), one of the nickel(II) centers is coordinated by four N-atoms of the tren ligand, one O-atom of the carboxylate group of the amino acidato ligand and one H2O molecule. The other nickel(II) center is also coordinated by the four N-atoms of the tren ligand, one carboxylic O-atom and the amino N-atom of the amino acidato ligand, resulting in an asymmetric dinuclear core with chromophores of NiN4O2 and NiN5O. In the polymeric {[Ni2(tren)2(dl-histinato)](ClO4)3·1.5H2O}n(4), the imidazole N-atom is also involved in ligation with nickel(II) and both nickel(II) centers have the same chromophore described as NiN5O. The Ni...Ni distances are in the 5.5199(10)–5.5807(15)A range. Analyses of the magnetic properties of complexes (1), (3) and (4) show that a weak ferromagnetic interaction exists between the two nickel(II) centers.