Mixed-valence compounds based on heterometallic-oxo-clusters containing Sb(iii,v): crystal structures and proton conduction

Abstract

Two isostructural Co(Cd)-antimony-oxo tartrate cluster-based compounds with a one-dimensional (1-D) belt-like structure, namely H_9.2[Co(H₂O)₆]{M_0.5(H₂O)_3.5{M′(H₂O)₄[Sb^VO₆[Co_4.2(H₂O)₅Sb^III₆(μ₃-O)₂(tta)₆]]}}₂·nH₂O (M = Co, M′ = Co, n = 9 (1); M = Cd_0.39/Co_0.61, M′ = Cd_0.24/Co_0.76, n = 7 (2); H₄tta = tartaric acid), have been synthesized by solvothermal methods. It is noteworthy that the relatively rare mixed-valence Sb(III,V) exists in the structures. The anionic clusters in both compounds appear to be in a sandwich configuration; the top and bottom layers are based on {Sb₃(μ₃-O)(tta)₃} brackets, and the intermediate layer is occupied by {Sb^VO₆[Co_4.2(H₂O)₅]}. The title compounds have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, thermogravimetric analyses, and UV-Vis spectroscopy. We chose compound 2 as a representative to test its proton conductivity, and the results show that the conductivity can reach 1.42 × 10⁻³ S cm⁻¹ at 85 °C under 98% relative humidity.