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

Three copper(II) complexes, [CuL¹], [CuL²] and [CuL³] where L¹, L² and L³ 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, [(CuL¹)₂Na(ClO₄)(H₂O)] [CuL¹] (1), [(CuL²)₂Na(ClO₄)(H₂O)] (2) and [(CuL³)₂Na(ClO₄)(H₂O)] (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, over(H, ^) = g₁ β HS₁ + g₂ β HS₂ + J₁₂ S₁ S₂ + g₃ β HS₃ for complex 1 and over(H, ^) = g₁ β HS₁ + g₂ β HS₂ + J₁₂ S₁ S₂ for complexes 2 and 3 has been used to interpret the magnetic data. The best fit parameters obtained are: g₁ = g₂ = 2.07(0), J = -1.09(1) cm^-1 for complex 1, g₁ = g₂ = 2.06(0), J = -0.55(1) cm^-1 for complex 2 and g₁ = g₂ = 2.07(0), J = -0.80(1) cm^-1 for 3. Electrochemical studies displayed an irreversible Cu(II)/Cu(I) one-electron reduction process.