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

Ternary copper(II) complexes containing reduced Schiff base ligands (N-(2-hydroxybenzyl)-alpha-amino acid, where alpha-amino acid = glycine (H(2)sgly), L-alanine (H(2)sala) and L-valine (H(2)sval)) and 1,10-phenanthroline (phen) have been synthesized and characterized. The neutral mononuclear Cu-II complexes [Cu(L)(phen)].xH(2)O (L = sgly (1), sala (2), sval (3)) have been prepared from Cu(OAc)(2).H2O, H2L, phen, LiOH in the ratio 1 : 1 : 1 : 2 in H2O-MeOH. The monodeprotonated Cu-II complexes [Cu(HL)(phen)](ClO4).xH(2)O (L = Hsgly (4), Hsala (5), Hsval (6)) have been obtained from Cu(ClO4)(2).6H(2)O, H2L, phen, LiOH in the ratio 1 : 1 : 1 : 1 in H2O-MeOH. The dinuclear Cu-II complexes [Cu-2(L)(phen)(3)](ClO4)(2).xH(2)O (L = sgly (7), sala (8), sval (9)) were the only product isolated instead of 1-3 when Cu(ClO4)(2).6H(2)O was used in the place of Cu(OAc)(2).H2O. 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) Angstrom in 4, and 2.73(4) and 2.79(4) Angstrom 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 mu(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)