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

Ternary copper(II) complexes containing reduced Schiff base ligands (N-(2-hydroxybenzyl)amino acid, where -amino acid = glycine (H2sgly), Lalanine (H2sala) and L-valine (H2sval)) and 1,10-phenanthroline (phen) have been synthesized and characterized. The neutral mononuclear CuII complexes [Cu(L)(phen)]·xH2O (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 CuII complexes [Cu(HL)(phen)](ClO4)·xH2O (L = Hsgly (4), Hsala (5), Hsval (6)) have been obtained from Cu(ClO4)2·6H2O, H2L, phen, LiOH in the ratio 1 1 1 1 in H2O–MeOH. The dinuclear CuII complexes [Cu2(L)(phen)3](ClO4)2·xH2O (L = sgly (7), sala (8), sval (9)) were the only product isolated instead of 1–3 when Cu(ClO4)2·6H2O 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 CuII–OH distances, 2.446(3) in 4, and 2.73(4) and 2.79(4) 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 µeff 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=½ chain model gave a J value of 1.2 cm–1.