Facile synthesis of Cu(II) complexes of monocondensed N,N,N donor Schiff base ligands: Crystal structure, spectroscopic and magnetic properties

Abstract

Four new copper(II) complexes, [(CuL 1N 3) 2](ClO 4) 2 ( 1), [(CuL 2N 3) 2](ClO 4) 2 ( 2), [CuL 3(N 3)(ClO 4)] n ( 3) and [CuL 4(μ-1,1-N 3)(μ-1,3-N 3)(ClO 4)] n ( 4) where L 1 = N 1-pyridin-2-yl-methylene-propane-1,3-diamine, L 2 = N 1-(1-pyridin-2-yl-ethylidene)propane-1,3-diamine, L 3 = N 1-(1-pyridin-2-yl-ethylidene)ethane-1,2-diamine and L 4 = N 1-(1-pyridin-2-yl-ethylidene)propane-1,2-diamine are four tridentate N,N,N donor Schiff base ligands, have been derived and structurally characterized by X-ray crystallography. Compounds 1 and 2 consist of double basal–apical end-on (EO) azide bridged dinuclear Cu II complexes with square-pyramidal geometry. In complex 3 the square planar mononuclear [CuL 3(N 3)] units are linked by weakly coordinated perchlorate ions in the axial positions of Cu II to form a one-dimensional chain. Two such chains are connected by hydrogen bonds involving perchlorate ions and azide groups. Compound 4 consists of 1-D chains in which the Cu II ions with a square-pyramidal geometry are alternately bridged by single EO and end-to-end (EE) azido ligands, both adopting a basal–apical disposition. Variable temperature (300–2 K) magnetic susceptibility measurements and magnetization measurements at 2 K have been performed. The results reveal that complexes 1 and 2 are antiferromagnetically coupled through azido bridges ( J = −12.18 ± 0.09 and −4.43 ± 0.1 cm −1 for 1 and 2, respectively). Complex 3 shows two different magnetic interactions through the two kinds of hydrogen bonds; one is antiferromagnetic ( J 1 = −9.69 ± 0.03 cm −1) and the other is ferromagnetic ( J 2 = 1.00 ± 0.01 cm −1). From a magnetic point of view complex 4 is a ferromagnetic dinuclear complex ( J = 1.91 ± 0.01 cm −1) coupled through the EO bridge only. The coupling through the EE bridge is practically nil as the N(azido)–Cu II (axial) distance (2.643 Å) is too long.