Synthesis and proton conductivity of two novel molybdate polymers

Abstract

Two novel molybdate polymers, H₄[Co(phen)₃]₂[NaO(H₂O)(τ-Mo₈O₂₆)]₂·2H₂O (1) and H₄[TEDA] [γ-Mo₈O₂₆]·3H₂O (2), (phen = 1,10′-phenanthroline, TEDA = triethylene diamine), were successfully synthesized by a hydrothermal method with MoCl₅. Single-crystal X-ray diffraction shows that 1 was a dimer-octamolybdate polymer connected by two Na⁺ cation, and it is the first molybdate dimer-polymer of [τ-Mo₈O₂₆]. Compound 2 was an extended 1D octamolybdate chain connected by contiguous [γ-Mo₈O₂₆]. Both 1 and 2 have 1D hydrogen-bond chains for proton-conducting pathways and free H⁺ counter cations as proton donors. These features make them suitable for potential proton-conducting solid crystal materials. The outstanding conductivities of 3.06 × 10⁻³ S cm⁻¹ for 1 and 4.18 × 10⁻⁴ S cm⁻¹ for 2 were achieved at 85 °C under 97% RH.