Inorganic-Organic Hybrid Crystals Derived from Polyoxovanadate and Ionic-Liquid toward Promising Conductive Materials

Conductive polyoxovanadate inorganic-organic hybrid crystals comprising alkaline earth metal (divalent) cations were successfully obtained with the use of an ionic-liquid cation having imidazolium and methacryloyl moieties (denoted as MAImC₁). Two types of crystals containing decavanadate ([V₁₀O₂₈]⁶⁻, V₁₀) anion were obtained as [MAImC₁]₂Ca₂[V₁₀O₂₈] ⋅ 16H₂O ⋅ 2 C₂H₅OH (MAImC₁−Ca−V₁₀) and [MAImC₁]₂Mg₂[V₁₀O₂₈] ⋅ 18H₂O ⋅ 2 C₂H₅OH (MAImC₁−Mg−V₁₀). Connection modes of the divalent cations were different: Ca²⁺ cations were connected to V₁₀ to form a {[Ca(H₂O)₅]₂V₁₀O₂₈]}²⁻ anion in MAImC₁−Ca−V₁₀, while a discrete [V₁₀O₂₈]⁶⁻ and hydrated [Mg(H₂O)₆]²⁺ were present in MAImC₁−Mg−V₁₀. Conductivities under a fully humidified condition at 353 K (80 °C) were high values of 3.0×10⁻⁴ S cm⁻¹ for MAImC₁−Ca−V₁₀ and 3.3×10⁻³ S cm⁻¹ for MAImC₁−Mg−V₁₀, respectively. The higher conductivity under hydrated conditions suggests proton as a conductive carrier. The better conductivity of MAImC₁−Mg−V₁₀ is plausibly derived from the more effective hydrogen-bonded network in the crystal lattice.