Stabilizing γ-Alkyltin-Oxo Keggin Ions by Borate Functionalization.

We report a hierarchical self-assembly engineering of tin-oxo clusters from nanosized hydrophobic clusters to a single-layer film of assembled clusters. These clusters are derivatives of the previously reported Na-centered butyltin Keggin ions, but they are bicapped with butyltin and with borate ligands. The formulas γ-[( n-BuSn)14(OCH3)10(OH)3O9(NaO4)(HBO3)2] and γ-[( n-BuSn)14(OCH3)10(OH)3O9(NaO4)(PhBO2)2] were determined from single-crystal X-ray diffraction and bulk solution characterization including small-angle X-ray scattering, electrospray ionization mass spectrometry, and multinuclear and multidimensional NMR (119Sn, 13C, and 1H). Solution characterization confirms that borate functionalization inhibits the solution-phase β-γ Keggin isomer interconversion that was recognized prior for uncapped butyltin clusters, and in this case, the γ isomer is favored. The assembly of the γ-NaSn14BO3 clusters into a homogeneous Langmuir-Blodgett monolayer is the first step toward creating nanopatterned films for microelectronic devices.