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 [Cu₃L(dmso)₅(H₂O)][ClO₄]₂ ·H₂O {H₄L = 2,6-bis[(5-substituted salicylidene)hydrazinocarbonyl]pyridine; L = L¹, R = H; L = L², R = Me₃; L = L³, R = Bu^t; L = L⁴, R = OMe₃; L = L⁵, R = Cl; L = L⁶, 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 [Cu₃L¹(dmso)₅(H₂O)][ClO₄ ]₂·H₂O has been established by X-ray diffraction. The structure consists of a Cu^IICu^IICu^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 L¹ 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^IICu^IICu^II are good mediators for spin-exchange interactions. Cyclic voltammetry of complex 1 showed one oxidation wave attributed to Cu^IICu^IICu^II →& -e^- Cu^IICu^IIICu ^II, a one-electron transfer reduction peak due to Cu^IICu^IICu^II →& +e ^- Cu^IICu^ICu^II and a two-electron transfer wave established as Cu^IICu^ICu^II → +2e^-  Cu^ICu^ICu^I.

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