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Keggin‐type polyaluminum cations belong to a unique class of compounds with their large positive charge, hydroxo bridges, and divergent isomerization/oligomerization. Previous reports indicated that oligomerization of this species can only occur through one isomer (δ), but herein we report the isolation of largest Keggin‐type cluster that occurs through self‐condensation of four ϵ‐isomers ϵ‐GeAl₁₂⁸⁺to form [Ge₄O₁₆Al₄₈(OH)₁₀₈(H₂O)₂₄]²⁰⁺cluster (Ge₄Al₄₈). The cluster was crystallized and structurally characterized by single‐crystal X‐ray diffraction (SCXRD) and the elemental composition was confirmed by ICP‐MS and SEM‐EDS. Additional dynamic light scattering experiments confirms the presence of theGe₄Al₄₈in thermally aged solutions. DFT calculations reveal that a single atom Ge substitution in tetrahedral site of ϵ‐isomer is the key for the formation ofGe₄Al₄₈because it activates deprotonation at key surface sites that control the self‐condensation process.

Keggin‐type polyaluminum cations belong to a unique class of compounds with their large positive charge, hydroxo bridges, and divergent isomerization/oligomerization. Previous reports indicated that oligomerization of this species can only occur through one isomer (δ), but herein we report the isolation of largest Keggin‐type cluster that occurs through self‐condensation of four ϵ‐isomers ϵ‐GeAl₁₂⁸⁺to form [Ge₄O₁₆Al₄₈(OH)₁₀₈(H₂O)₂₄]²⁰⁺cluster (Ge₄Al₄₈). The cluster was crystallized and structurally characterized by single‐crystal X‐ray diffraction (SCXRD) and the elemental composition was confirmed by ICP‐MS and SEM‐EDS. Additional dynamic light scattering experiments confirms the presence of theGe₄Al₄₈in thermally aged solutions. DFT calculations reveal that a single atom Ge substitution in tetrahedral site of ϵ‐isomer is the key for the formation ofGe₄Al₄₈because it activates deprotonation at key surface sites that control the self‐condensation process.