Synthesis, characterization and properties of ternary copper(II) complexes containing reduced Schiff base N-(2-hydroxybenzyI)-α-amino acids and 1,10-phenanthroline

Abstract

Ternary copper(II) complexes containing reduced Schiff base ligands (N-(2-hydroxybenzyl)-α-amino acid, where α-amino acid = glycine (H 2sgly), L-alanine (H 2sala) and L-valine (H 2sval)) and 1,10-phenanthroline (phen) have been synthesized and characterized. The neutral mononuclear Cu II complexes [Cu(L)(phen)]·xH 2O (L = sgly (1), sala (2), sval (3)) have been prepared from Cu(OAc) 2·H 2O, H 2L, phen, LiOH in the ratio 1 : 1 : 1 : 2 in H 2O-MeOH. The monodeprotonated Cu II complexes [Cu(HL)(phen)](ClO 4)·xH 2O (L = Hsgly (4), Hsala (5), Hsval (6)) have been obtained from Cu(ClO 4) 2·6H 2O, H 2L, phen, LiOH in the ratio 1 : 1 : 1 : 1 in H 2O-MeOH. The dinuclear Cu II complexes [Cu 2(L)(phen) 3](ClO 4) 2·xH 2O (L = sgly (7), sala (8), sval (9)) were the only product isolated instead of 1-3 when Cu(ClO 4) 2·6H 2O was used in the place of Cu(OAc) 2·H 2O. The electronic spectral titration experiments indicate that the neutral mononuclear compounds could be converted to protonated 4-6 but not vice versa. The protonated phenolic oxygen is involved in medium to weak interaction with Cu II-OH distances, 2.446(3) Å in 4, and 2.73(4) and 2.79(4) Å in 5. Compound 4 is a mononuclear cation while 5 is a helical coordination polymer in the solid state with the carboxylate group in anti-anti bridging mode. The structures of 1,4,5 and 7 have been determined by X-ray crystallography. Variable temperature magnetic measurements of the helical polymer 5 showed very weak ferromagnetic coupling with μ eff per Cu remaining constant at 1.80 BM between 300 and 30 K, then a rapid increase to 2.07 BM at 4 K. Fitting to a Heisenberg S = 1/2 chain model gave a J value of 1.2 cm -1. © The Royal Society of Chemistry 2003.