Co-operation of π⋯π, Cu(II)⋯π, carbonyl⋯π and hydrogen-bonding forces leading to the formation of water cluster mimics observed in the reassessed crystal structure of [Cu(mal)(phen)(H 2O)]2·3H 2O (H 2mal = malonic acid, phen = 1,10-phenanthroline)

Abstract

A copper(II) malonate complex with formula [Cu(mal)(phen)(H 2O)] 2·3H 2O ( 1) [H 2mal = malonic acid, phen = 1,10-phenanthroline] has been synthesized and its crystal structure has been re-determined with an improved R value (the compound 1 was originally synthesized and crystallographically characterized by Kwik et al. with R = 0.047, see: J. Chem. Soc. Dalton Trans. (1986) 2529) with the water hydrogen atom positions located. This has led to the revelation that the water molecules organize around the carboxylate group of the malonate ligand forming tetramer, hexamer and octameric water cluster mimics. These cooperative hydrogen-bonding forces and various π-forces (π⋯π, Cu(II)⋯π, carbonyl⋯π) involving 1,10-phenanthroline aromatic rings determine the overall packing of the molecular units in the unit cell. There exists two identical monomers in the asymmetric unit with Z // = 2. TG measurements reveal the loss of water molecules that are all released at 120 °C. The water sorption/desorption process is reversible as supported by FTIR spectroscopic and XRPD studies.