Space-Confined Nucleation of Semimetal-Oxo Clusters within a [H₇P₈W₄₈O₁₈₄]³³– Macrocycle: Synthesis, Structure, and Enhanced Proton Conductivity

Spatially confined assembly of semimetallic oxyanions (AsO 3 3– and SbO 3 3– ) within a [H 7 P 8 W 48 O 184 ] 33– (P 8 W 48 ) macrocycle has afforded three nanoscale polyanions, [{As III 5 O 4 (OH) 3 } 2 (P 8 W 48 O 184 )] 32– ( As 10 ), [(Sb III OH) 4 (P 8 W 48 O 184 )] 32– ( Sb 4 ), and [(Sb III OH) 8 (P 8 W 48 O 184 )] 24– ( Sb 8 ), which were crystallized as the hydrated mixed-cation salts (Me 2 NH 2 ) 13 K 7 Na 2 Li 10 [{As III 5 O 4 (OH) 3 } 2 (P 8 W 48 O 184 )]·32H 2 O ( DMA-KNaLi-As 10 ), K 20 Li 12 [(Sb III OH) 4 (P 8 W 48 O 184 )]·52H 2 O ( KLi-Sb 4 ), and (Me 2 NH 2 ) 8 K 6 Na 5 Li 5 [(Sb III OH) 8 (P 8 W 48 O 184 )]·65H 2 O ( DMA-KNaLi-Sb 8 ), respectively. A multitude of solid- and solution-state physicochemical techniques were employed to systematically characterize the structure and composition of the as-made compounds. The polyanion of As 10 represents the first example of a semimetal-oxo cluster-substituted P 8 W 48 and accommodates the largest As III -oxo cluster in polyoxometalates (POMs) reported to date. The number of incorporated SbO 3 3– groups in Sb 4 and Sb 8 could be customized by a simple variation of Sb III -containing precursors. Encapsulation of semimetallic oxyanions inside P 8 W 48 sets out a valid strategy not only for the development of host–guest assemblies in POM chemistry but also for their function expansion in emerging applications such as proton-conducting materials, for which DMA-KNaLi-As 10 showcases an outstanding conductivity of 1.2 × 10 –2 S cm –1 at 85 °C and 70% RH.