Citrate, in collaboration with a guanidinium ion, as a generator of cubane-like complexes with a range of metal cations: Synthesis, structures, and magnetic properties of [C(NH2)3]8[(M II)4(cit)4]·8H2O (M = Mg, Mn, Fe, Co, Ni, and Zn; cit = citrate)

Abstract

Aqueous reaction mixtures containing citric acid, guanidinium carbonate, and a range of metal cations (Mg2+, Mn2+, Fe2+, Co2+, Ni2+, and Zn2+) at room temperature give crystalline products of composition [C(NH2)3] 8[(MII)4(cit)4]· 8H 2O (cit = citrate). In all cases, the crystals are suitable for single-crystal X-ray diffraction studies, which reveal that the compounds are isostructural (space group P42/n; a ∼ 16.2 Å, and c ∼ 11.5 Å). As was intended, cubane-like [M4(cit) 4]8- complex anions are present. The individual citrate units are chiral, but each cubane unit contains two of one hand and two of the other, related around an S4 axis. The cubane units are involved in no less than 40 H-bon..