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

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 (mu-alkoxo)(mu-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 -132cm(-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(.)H(2)O 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. (c) 2005 Elsevier Ltd. All rights reserved.