Synthesis and structural behavior of ternary copper(II) complexes containing reduced Schiff base N-(2-hydroxybenzyl)-4-aminobutyric acid and 1,10-phenanthroline

Abstract

Ternary copper(II) complexes containing reduced Schiff base ligand N-(2-hydroxybenzyl)-4-aminobutyric acid (H 2Sab4) and 1,10-phenanthroline (phen) have been synthesized and characterized. Compound [Cu(Sab4)(phen)(H 2O)] · 5H 2O ( 1) was prepared from Cu(OAc) 2 · H 2O, H 2Sab4, phen, and LiOH in the ratio 1:1:1:2 in H 2O–MeOH. Green crystals of [Cu 3(Sab4) 2(phen)(H 2O) 2](ClO 4) 2 · 0.5H 2O ( 2) were isolated first from Cu(ClO 4) 2 · H 2O, H 2Sab4, phen, and LiOH in the ratio of 1:1:1:1. The filtrate furnished dark blue rhombohedral crystals of [Cu(H 2Sab4) 2(phen)](ClO 4) 2 ( 3), within a week. When the ratio of base was doubled, [Cu 2(Sab4)(phen) 3](ClO 4) 2 · 3H 2O ( 4) was the only product isolated. The crystal structures of 1, 3 and 4 have been determined. In the zwitterionic mononuclear complex 1 the Cu(II) has square pyramidal geometry with a water molecule at the apical position and the carboxylate anion hydrogen bonded to the lattice water molecules. Five highly ordered water molecules present in the lattices in 1 generate an interesting 3D hydrogen bond network in the solid state. In 3, the carboxylic acid is deprotonated by the secondary amino group of the ligand to form a zwitterion. The carbonyl O atoms and the protons of phenolic and –NH 2 + groups of the ligands are involved in extensive hydrogen bond network. The presence of intra and intermolecular π⋯π interactions between the two ligands is evident in 4.