Stabilization of Alkyltin γ-Keggin Clusters by 2, 5-Dihydroxyterephthalate Ligands

The Keggin clusters are one kind of the most representative molecular structures in the field of metal-oxo clusters. Although the different types of Keggin clusters with various components were reported, the research about γ-Keggin isomer remains less developed. This is ascribed to the difficulty in obtaining the stable pure γ-Keggin cluster for the structural isomerization. In this study, we adopted a ligand stabilization strategy to get the stable pure γ-Keggin structure [(n-BuSn)₁₂(NaO₄)(OH)₂₄](DHTA)_2.5 ⋅ DMF ⋅ H₂O (CTGU-SnC-10). Different from the reported mixed neutral-charge alkytin β, γ isomers, the NaSn₁₂ cluster in the CTGU-SnC-10 is a cationic pentavalent γ-Keggin structure without isomerization. Besides the electrostatic interaction, the NaSn₁₂ cationic clusters have a strong hydrogen-bond interaction with polycarboxylic ligands, resulting in the formation of a 3D hydrogen-bonded framework. These are conducive to stabilizing the γ-Keggin structure. Moreover, the CTGU-SnC-10 exhibits high hydrophobicity and a small band gap due to the organic functional groups of the framework.