Syntheses, and structural, magnetic, and redox properties of multinuclear copper catecholates

Abstract

Interaction of copper salts with a ligand (H₂L¹) obtained by condensation of 3,4-dihydroxybenzaldehyde with 2-aminomethylpyridine allows one to isolate a nitrato [{Cu(HL¹)(NO₃)}₄], (1), a chloro [{Cu(HL¹)Cl}₂], (2), and an acetato [{CuL¹(CH₃CO₂)}₄], (3), derivative. The acetato derivative [{Cu₂L²(CH₃CO₂)₂}₂], (4), of a ligand (H₂L²) prepared from 2-(2′-aminoethyl)pyridine has been isolated in the crystalline state and its structure solved by X-ray diffractometry. It crystallizes in the space group P1, with a= 8.365(2), b= 9.667(1), c= 12.556(1)Å, α= 98.40(2), β= 103.97(2), and γ= 94.26(2)°. The tetranuclear arrangement results from dimerization of the dinuclear unit comprising one copper atom in the chelated site (O₂) and one in the lateral site (N₂O) through the external catechol oxygen. Complex (1) crystallizes in the space group P2₁/n, with a= 20.47(5), b= 21.27(5), c = 14.31 (7)Å, and β= 93.93(7)°. It is tetranuclear in the solid state and adopts a distorted cubane structure with a Cu₄O₄core, the four copper atoms being bridged by the internal catechol oxygens of the ligand molecules. The magnetic properties of both compounds are interpreted with the magnetic orbital concept. Electrochemical studies revealed that, in (1), both the metal and the ligand are electroactive.