Incorporation of a sodium ion guest in the host of copper(II)-Schiff-base complexes: Structural characterization and magnetic study

Abstract

Three copper(II) complexes, [CuL 1], [CuL 2] and [CuL 3] where L 1, L 2 and L 3 are the tetradentate di-Schiff-base ligands prepared by the condensation of acetylacetone and appropriate diamines (e.g. 1,2-diaminoethane, 1,2-diaminopropane and 1,3-diaminopropane, respectively) in 2:1 ratios, have been prepared. These complexes act as host molecules and include a guest sodium ion by coordinating through the oxygen atoms to result in corresponding new trinuclear complexes, [(CuL 1) 2Na(ClO 4)(H 2O)][CuL 1] ( 1), [(CuL 2) 2Na(ClO 4)(H 2O)] ( 2) and [(CuL 3) 2Na(ClO 4)(H 2O)] ( 3) when crystallized from methanol solution containing sodium perchlorate. All three complexes have been characterized by single crystal X-ray crystallography. In all the complexes, the sodium cation has a six-coordinate distorted octahedral environment being bonded to four oxygen atoms from two Schiff-base complexes of Cu(II) in addition to a perchlorate anion and a water molecule. The copper atoms are four coordinate in a square planar environment being bonded to two oxygen atoms and two nitrogen atoms of the Schiff-base ligand. The variable temperature susceptibilities for complexes 1– 3 were measured over the range 2–300 K. The isotropic Hamiltonian, H ^ = g 1 β HS 1 + g 2 β HS 2 + J 12 S 1 S 2 + g 3 β HS 3 for complex 1 and H ^ = g 1 β HS 1 + g 2 β HS 2 + J 12 S 1 S 2 for complexes 2 and 3 has been used to interpret the magnetic data. The best fit parameters obtained are: g 1 = g 2 = 2.07(0), J = −1.09(1) cm −1 for complex 1, g 1 = g 2 = 2.06(0), J = −0.55(1) cm −1 for complex 2 and g 1 = g 2 = 2.07(0), J = −0.80(1) cm −1 for 3. Electrochemical studies displayed an irreversible Cu(II)/Cu(I) one-electron reduction process.