Synthesis, electrochemical and magnetic properties of Cu3 complexes of a series of new compartmental trinucleating ligands H4L

Abstract

A series of linear trinuclear copper(II) complexes [Cu 3 L(dmso) 5 (H 2 O)][ClO 4 ] 2 ·H 2 O {H 4 L = 2,6-bis[(5-substituted salicylidene)hydrazinocarbonyl]pyridine; L = L 1 , R = H; L = L 2 , R = Me 3 ; L = L 3 , R = Bu t ; L = L 4 , R = OMe 3 ; L = L 5 , R = Cl; L = L 6 , R = Br; dmso = dimethyl sulfoxide} have been synthesized and characterized on the basis of infrared and electronic spectra, electrochemical and variable-temperature (80–300 K) magnetic measurements. The crystal and molecular structure of [Cu 3 L 1 (dmso) 5 (H 2 O)][ClO 4 ] 2 ·H 2 O has been established by X-ray diffraction. The structure consists of a Cu II Cu II Cu II trinuclear cation, unco-ordinated perchlorate anions, and a water molecule of crystallization. Each copper ion is in a square-pyramidal environment. The compartmental ligand L 1 co-ordinates in two different modes: (i) as tridentate in the terminal compartment defined by the hydrazonic carbonyl, hydrazonic nitrogen and phenolic oxygen; (ii) tridentate in the central chamber defined by the pyridyl nitrogen and two hydrazonic nitrogens. Cryomagnetic investigations reveal a moderately strong antiferromagnetic spin exchange among adjacent copper(II) ions in each complex (J = -40 to -65 cm -1 ), showing that the compartmental ligands of the Cu II Cu II Cu II are good mediators for spin-exchange interactions. Cyclic voltammetry of complex 1 showed one oxidation wave attributed to Cu II Cu II Cu II →& -e - Cu II Cu III Cu II , a one-electron transfer reduction peak due to Cu II Cu II Cu II →& +e - Cu II Cu I Cu II and a two-electron transfer wave established as Cu II Cu I Cu II →+2e - Cu I Cu I Cu I .