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 (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.