Formation of binuclear neutral Copper(II) complexes based on p-tert-butyl- calix[4]arene and thiacalix[4]arene in 1,3-A conformation bearing four catechols at their lower rim

Abstract

Two new multivalent ligands 1 and 2, based on calix[4]arene and thiacalix[4]arene backbones in 1,3-Alternate conformation, bearing four iminocatechol coordinating units have been prepared and structurally characterized both in solution and in the crystalline phase. Combinations of compounds 1 and 2 with Cu(II) afford neutral binuclear complexes 1-Cu2 and 2-Cu2, characterized in the solid state. In both cases, the metal centre, surrounded by a O3N set of heteroatoms, adopts a deformed square planar coordination geometry. In solution, the propensity of ligands 1 and 2 to bind M2+ cations ((M=Co, Ni, Cu and Zn) was also demonstrated. In 1/1 MeOH/CHCl3 mixture and at room temperature, the following stability sequence Ni2+<Zn2+<Co2+≪Cu2+ was observed for both binuclear 1-M2 and 2-M2 complexes.