Solvothermal synthesis of [Cr7S8(en)8Cl2]Cl3·2H2O with magnetically frustrated [Cr7S8]5+ double-cubes

A novel transition metal chalcohalide [Cr7S8(en)8Cl2]Cl3·2H2O, with [Cr7S8]5+ dicubane cationic clusters has been synthesized by a low temperature solvothermal method using dimethyl sulfoxide (DMSO) and ethylenediamine (en) solvents. Ethylenediamine ligand exhibits bi- and monodentate coordination modes, in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, highly negative Weiss constant, q  = -224(2) K, obtained from Curie-Weiss fit of inverse susceptibility suggests strong antiferromagnetic (AFM) interactions between S = 3/2 Cr(III) centers. Due to the complexity of the system with (2S + 1)7 = 16384 microstates from seven Cr3+ centers, a simplified model with only two exchange constants was used for simulations. Density-functional theory (DFT) calculations yielded the two exchange constants to be J1 = -21.4 cm-1 and J2 = -30.2 cm-1, confirming competing AFM coupling between the shared Cr3+ center and the peripheral Cr3+ ions of the dicubane cluster. The best simulation of the experimental data was obtained with J1 = -20.0 cm-1 and J2 = -21.0 cm-1, in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr3+ ions as compared to the AFM exchange between the central and peripheral Cr3+ ions. This compound can be used to explore the synthesis of magnetically frustrated systems of polymeric nature, containing dicubane transition meta-chalcogenide cations and charge balancing halide anions.