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

Abstract

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 (1) and Cs₈[H₄(GeW₉Nb₃O₄₀)₂(Mo₂O₄C₂O₄)]·17H₂O (2), and two tetrameric compounds Cs₁₅(NH₄)[(SiW₉Nb₃O₄₀)₄(Mo₄O₆)]·42H₂O (3) and Cs₁₀K₅[H(GeW₉Nb₃O₄₀)₄(Mo₄O₆)]·39H₂O (4). Notably, this is the first report of Mo/W/Nb ternary mixed-addendum POMs. In addition, compounds 3 and 4 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.