Assembly of [Mo2O2S2]2+-Based Crystalline Complexes Directed by [AsO4]3- Template: Synthesis and Proton Conduction

Traditional proton-conducting materials cannot retain high conductivity under low humidity and elevated temperatures, restricting their practical applications in clean energy fuel cells and other related devices; by contrast, crystalline materials built from [Mo2O2S2]2+ units can address this critical issue. Accordingly, guided by [AsO4]3- templates, this work successfully synthesizes and fully characterizes two novel complexes containing [Mo2O2S2]2+ units. Namely, H3[AsO4(Mo2O2S2)3(OH)3(L1)3]·10H2O (1) and H6K12I4[(AsO4)4(Mo2O2S2)10O4(L2)2]·[(Mo2O2S2)4(OH)8(MoO6)]·18H2O (2) (L1 = 3-aziridinecarboxylate; L2 = succinate) were successfully synthesized and comprehensively characterized. Proton conduction performance tests reveal that complex 2 exhibits superior proton conductivity compared with complex 1, and such performance discrepancy is fundamentally originated from their structural differences. Specifically, the elaborate three-dimensional framework of complex 2 constructs efficient and high-quality transport channels for proton migration, endowing it with better conduction capability. Further mechanistic investigations demonstrate that complex 1 achieves proton transport via a combined mechanism of carrier diffusion and proton jumping, whereas proton conduction in complex 2 solely relies on carrier diffusion.