Synthesis, characterization and properties of ternary copper(ii) complexes containing reduced Schiff baseN-(2-hydroxybenzyl)-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 (H₂sgly), L-alanine (H₂sala) and L-valine (H₂sval)) and 1,10-phenanthroline (phen) have been synthesized and characterized. The neutral mononuclear Cu^II 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 Cu^II 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 Cu^II 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 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 = ½ chain model gave a J value of 1.2 cm⁻¹.