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

Abstract

Dicopper(II) complexes [Cu 2 L(O 2 CCH CHC 6 H 4 - p -OH)(MeOH)] · MeOH ( 1 · MeOH) and [Cu 2 L(O 2 CCH CHC 6 H 4 - p -OH)] · H 2 O ( 2 · H 2 O) having a carboxylate ligand with a p -hydroxycinnamyl moiety and the pentadentate Schiff base N , N ′-1,3-diyl-bis(acetylacetoneimine)propan-2-ol (H 3 L) in its trianionic form, are prepared and structurally characterized by X-ray crystallography. The antiferromagnetically coupled dicopper(II) complexes show hydrogen bonding interactions to form helical supramolecular structures of different conformations. 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 · 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.