Lewis Acid Guests in a {P 8 W 48 } 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 {P 8 W 48 }‐archetype phosphotungstate has afforded a nanoscale 16‐Al III ‐32‐oxo cluster and its Ga III analogue that contain the largest number of Al III /Ga III ions yet found in polyoxometalate (POM) chemistry. Interestingly, the rich Lewis acid Al III 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.