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

Two isostructural Co(Cd)-antimony-oxo tartrate cluster-based compounds with a one-dimensional (1-D) belt-like structure, namely H 9.2 [Co(H 2 O) 6 ]{ M 0.5 (H 2 O) 3.5 { M '(H 2 O) 4 [Sb V O 6 [Co 4.2 (H 2 O) 5 SbIII6(μ 3 -O) 2 (tta) 6 ]]}} 2 · n H 2 O ( M = Co, M ' = Co, n = 9 (1); M = Cd 0.39 /Co 0.61 , M ' = Cd 0.24 /Co 0.76 , n = 7 (2); H 4 tta = 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 {Sb 3 (μ 3 -O)(tta) 3 } brackets, and the intermediate layer is occupied by {Sb V O 6 [Co 4.2 (H 2 O) 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.