Effect of a pentadentate Schiff base on the helical supramolecular structures of (μ-alkoxo)(μ-carboxylato)dicopper(II) complexes

Abstract

Two new asymmetrically dibridged dicopper(II) complexes with a pentadentate Schiff base and p-hydroxycinnamate are prepared and structurally characterized by X-ray crystallography. The complexes have an asymmetrically dibridged (μ-alkoxo)(μ-carboxylato)dicopper(II) core with an alkoxo bridge from the Schiff base and the carboxylate showing a three-atom bridging mode. Variable-temperature magnetic studies show the complexes having an antiferromagnetically coupled spin system giving a singlet-triplet energy separation of -160 and -132 cm^-1 for 1 and 2, respectively. Complex 1, with a shorter Cu-OR-Cu angle, displays greater antiferromagnetic spin coupling. Besides the Cu-OR-Cu angle, the role of the carboxylate ligand and the supramolecular structure in the spin coupling phenomena is observed. Complex 1 · MeOH shows the formation of intermolecular hydrogen bonds involving the axial methanol and the pentadentate Schiff base terminal oxygen atom. There is additional hydrogen bonding interactions involving the p-hydroxy group of the carboxylate, the lattice methanol and the terminal oxygen atom. The crystal structure of complex 2 · H₂O displays the presence of a helical supramolecular structure due to hydrogen bonding interactions involving the pendant p-hydroxy group and the bridging oxygen atom of the carboxylate.