Assembly of Four Ternary Polyoxometalate Aggregates by Integrating Presynthesized {XW₉Nb₃O₄₀} (X = Si/Ge) Units Using Molybdenum-Oxo Clusters

Polyoxometalates (POMs) have good potential for applications in different fields, including conducting materials, optics, and electrocatalysis. Of particular significance is the synthesis and development of addendum POMs. Molybdenum-oxo clusters, which are renowned for their diverse structures and electronic properties, were utilized to facilitate the synthesis of innovative materials. Herein, we employed presynthesized {XW₉ Nb₃O₄₀} (X= Si/Ge) polyanions as secondary building units and different molybdenum-oxo clusters as linkers. Four new addendum POMs were constructed, including two dimeric compounds Cs₁₀[H₂(SiW₉Nb₃O₄₀)₂(Mo₂O₄C₂O₄)]·19H₂O (<b>1</b>) and Cs₈[H₄(GeW₉Nb₃O₄₀)₂(Mo₂O₄C₂O₄)]·17H₂O (<b>2</b>), and two tetrameric compounds Cs₁₅(NH₄)[(SiW₉Nb₃O₄₀)₄(Mo₄O₆)]·42H₂O (<b>3</b>) and Cs₁₀K₅[H(GeW₉Nb₃O₄₀)₄(Mo₄O₆)]·39H₂O (<b>4</b>). Notably, this is the first report of Mo/W/Nb ternary mixed-addendum POMs. In addition, compounds <b>3</b> and <b>4</b> facilitate the transfer of protons through extended hydrogen-bonding networks with conductivity values of 1.16 × 10^-2 and 7.73 × 10^-3 S·cm^-1 at 85 °C and 98% relative humidity, respectively. Furthermore, no discernible decline in conductivity was noted over the course of 10 h.