Protonated malonate: the influence of the hydrogen bonds on the magnetic behaviour

Abstract

One hydrogen malonato-bridged complex of formula [Cu(Hmal)₂] (1) and two polymorphous malonato-bridged complexes of formula [Cu(H₂O)(H₂mal)(mal)] (2 and 3), in which the three species of the malonate (H₂mal, Hmal⁻, and mal²⁻) are present, were synthesised and characterized by X-ray diffraction [H₂mal = malonic acid]. Their structures consist of corrugated malonate layers of [Cu(Hmal)₂] (1) and [Cu(H₂O)(H₂mal)(mal)] (2 and 3) units bridged by carboxylate–malonate groups. The layers are linked through hydrogen bonds leading to a three-dimensional network. Variable-temperature (1.9–290 K) magnetic susceptibility measurements indicate the occurrence of weak ferromagnetic interactions between the copper(II) ions through the carboxylate–malonate bridge. The effectiveness of magnetic exchange coupling is related to the degree of protonation of the malonate group.