Inorganic-organic hybrid materials have potential for the construction of functionalized materials. We can expect synergy of the merits derived from inorganic motifs bringing thermal stability as well as various functions, and from organic components which enable flexible control of molecular and built-up structures.

  Polyoxometalates are inorganic cluster anions having various physicochemical properties. The molecular design enables to change redox properties, and the selection of counter cations can improve thermal stability. Several polyoxometalates have been utilized as industrial catalysts. In addition, other characteristics such as photochromic and biological properties catch extensive attention from researchers. 

  We have successfully synthesized a rare series of hybrid crystals comprising functional inorganic clusters (polyoxometalates) and surfactant molecules. These hybrid crystals can precisely tune the composition, structure and function by changing the combination of polyoxometalate anion and surfactant cation. Selective introduction of proton and metal ions such as lithium, sodium, or potassium has been realized. 

  The hybrid crystals possess layered structure beneficial for the emergence of conductivity. We have synthesized hybrid crystals exhibiting anhydrous proton conductivity over 373 K. These hybrid crystals exhibit electric and proton conductivities, and are promising solid electrolytes or electrode materials for fuel-cell and rechargeable batteries.