Lewis Acid Guests in a {P8W48} Archetypal Polyoxotungstate Host: Enhanced Proton Conductivity via Metal‐Oxo Cluster within Cluster Assemblies

: Complexes made by hosts that completely surround their guests provide a means to stabilize reactive chemical intermediates, transfer biologically active cargo to a diseased cell, and construct molecular-scale devices. By the virtue of inorganic host-guest self-assembly, nucleation processes in the cavity of a {P8 W48 }-archetype phosphotungstate has afforded a nanoscale 16-AlIII -32-oxo cluster and its GaIII analogue that contain the largest number of AlIII /GaIII ions yet found in polyoxometalate (POM) chemistry. Interestingly, the rich Lewis acid AlIII centers within the Lewis base POM support shows an exceptional proton conductivity of 4.5×10-2  S cm-1 (85 °C, 70 % RH; RH: relative humidity), which is by far the highest conductivity reported among POM-based single-crystal proton conductors.