Fine tuning of coordination environments by anions on a series of Cu(II) dihydrazide complexes: Syntheses, structures, magnetic properties and solution phase anion exchange

Abstract

A series of Cu(II) dihydrazide complexes were synthesized using the reaction of Cu(II) salts with the ligand H2L, having molecular formulae [Cu3L2(BF4)(H2O)2](BF4) (1), [Cu3L2(NO3)2(H2O)2](H2O)3 (2), [Cu3L2(Cl)2(CH3OH)2](H2O)2 (3) and [Cu3L2(ClO4)2(H2O)2] (4) where H2L = 6,6′-((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene))bis(2-methoxyphenol). X-ray crystallography reveals that all the complexes exhibit a discrete trinuclear puckered structure where the anions bind to the metal centers. Due to differences in size and shape, the anions affect the geometry around the Cu(II) centers and distortions of the square pyramidal geometry are found. Anion binding also affects the planarity of the structure, the complexes having different twist angles. The structural differences are the origin of the variation in the magnetic interactions. DC magnetic susceptibilities reveal dominant antiferromagnetic interactions for the complexes 1–4, but the magnitude of magnetic interactions is different in each case. From the Curie-Weiss fitting of the χM−1 vs. T plot, the Curie-Weiss constant (θ) varies as 151.8, −95.5, −114.5 and −467.4 cm−1 for complexes 1, 2, 3 and 4, respectively. Also, from the fitting of the spin Hamiltonian by matrix diagonalization, J = −170 cm−1 and g = 2.16 for complex 1 and J = −249.7 cm−1 and g = 2.14 for complex 4 were obtained, whereas for complex 2, J1 = −110 cm−1, J2 = −1.7 cm−1 and g = 2.1, and for complex 3, J1 = −105 cm−1, J2 = +10 cm−1 and g = 2.04 were obtained. Furthermore, a solution phase anion exchange study reveals selective detection of chloride ions by the naked eye and this was supported by a UV–Vis study. A cyclic voltammetry study reveals irreversible redox features for complexes 1–4 and the effect of NaCl.