Guanidinium-Induced Intermolecular Hydrogen-Bonding Networks: An Effective Strategy for Achieving Superprotonic Conductivity in Molybdenum–Oxygen Clusters

Abstract As a class of inorganic clusters with precisely tunable structures, polyoxometalates (POMs) demonstrate great potential in the field of proton-conducting materials due to their inherent proton-transfer sites and functionalizable surface properties. In this study, utilizing the glyphosate (L1) and risedronic acid (L2) in combination with [Mo2O4(H2O)6]2+ building block, we have successfully synthesized two novel POM clusters: (CH6N3)6[(Mo6O19)(μ2-O)3(Mo2O4)2(L1)2]·3H2O (Complex 1) and H31Na11[(Mo2O4)2(MoO3)4(μ2-O)18(L2)2]·14H2O (Complex 2). The two complexes were characterized using single-crystal X-ray diffraction, infrared spectroscopy (IR), and thermogravimetric analysis (TGA), confirming that they possess stable polymetallic oxygen cluster frameworks and extensive hydrogen-bonding networks. Furthermore, under conditions of 75% relative humidity (RH) and 80 °C, Complexes 1 and 2 exhibit proton conductivities as high as 4.75 × 10–2 S cm–1 and 4.40 × 10–2 S cm–1, respectively, demonstrating excellent superprotonic conduction properties. This study provides innovative research insights and a theoretical basis for the design and preparation of proton-conducting materials based on polyoxometalates.