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, [(CuL¹N₃)₂](ClO₄)₂ (1), [(CuL²N₃)₂](ClO₄)₂ (2), [CuL³(N₃)(ClO₄)]_n (3) and [CuL⁴(μ-1,1-N₃)(μ-1,3-N₃)(ClO₄)]_n (4) where L¹ = N¹-pyridin-2-yl-methylene-propane-1,3-diamine, L² = N¹-(1-pyridin-2-yl-ethylidene)propane-1,3-diamine, L³ = N¹-(1-pyridin-2-yl-ethylidene)ethane-1,2-diamine and L⁴ = N¹-(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 [CuL³(N₃)] 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 (J₁ = −9.69 ± 0.03 cm⁻¹) and the other is ferromagnetic (J₂ = 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.