Syntheses, structural properties and catecholase activity of copper(ii) complexes with reduced Schiff baseN-(2-hydroxybenzyl)-amino acids

Abstract

A number of dicopper(II) complexes of reduced Schiff base ligands, N-(2-hydroxybenzyl)-amino acids [Cu₂L₂(H₂O)_x]·yH₂O (L = Sgly (1), D-Sala (2), L-Sala (3), DL-Sala (4), Sab2 (5), Sbal (6), Sab4 (7), Sval (8), Shis (9), Styr (10) and Stryp (11), x = 0–2 & y = 0–2) have been synthesized, and the solid-state structures of 4, 5,10 and 11 have been determined. The compounds 4 and 5 are binuclear in which the Cu(II) centres have square-pyramidal geometry with apical sites occupied by aqua ligands. In 10 and 11 one axial site is occupied by water and the other by an oxygen atom of the carboxylate group from the adjacent dimer through oxygen atoms to form 1D helical polymer. Variable temperature magnetic measurements of the dimer 4 and helical polymer 10 showed that they are typical for moderately strong antiferromagnetic coupling. All the complexes show significant catalytic activity on the oxidation of 3,5-di-tert-butylcatechol. The activity measured in terms of K_cat in the range 199–3800 h⁻¹ has been found to follow the order: 7 > 6 > 8 > 3 > 5 ∼ 2 ∼1 > 4 > 10 >9 > 11. The catalytic activity is found to increase with increasing the length of the methylene side chain of the amino acid in the reduced Schiff base ligands.