Versatile supramolecular self-assembly. Part I. Network formation and magnetic behaviour of the alkaline salts of the bis(malonate)cuprate(ii) anion

Abstract

Five malonate-containing copper(II) compounds of formula {[A(H₂O)_n]₂ [Cu(mal)₂(H₂O)_m]} [A = Li (1), Na (2), K (3), Rb (4) and Cs (5); H₂mal = malonic acid] have been synthetized and characterized by X-ray diffraction. The structure of these compounds consists of bis(malonate)cuprate(II) anions and alkaline cations that are held together by means of carboxylate bridges and water molecules leading to 3D networks. A study of the self-assembling of the bis(malonate)cuprate(II) and the alkaline cations is carried out, the size of the alkaline metal ion playing an important role in the control of the resulting malonate-bridged copper(II) structure. A regular alternation of layers of anionic malonate–copper(II) and cationic alkaline metal atoms occurs compounds 2–5. The alkaline metal ions are connected through μ-oxo bridges affording thus, different cationic motifs: dimers (1), single (2 and 3) and double helical chains (4) and layers (5). Depending on the alkaline cation, the bis(malonate)cuprate(II) units can be linked to each other through malonate carboxylate bridges giving rise to anionic networks which exhibit different topologies: monomers (1 and 5), chains (4) and layers (2 and 3). Variable-temperature (1.9–290 K) magnetic susceptibility measurements show the occurrence of ferromagnetic interactions [ranging from +0.77(1) to +0.90(1) cm⁻¹] between the copper(II) ions through the caboxylate–malonate bridge in the out-of-plane anti-anti conformation.