Toward Nanodevices: Synthesis and Characterization of the Nanoporous Surfactant-Encapsulated Keplerate (DODA)₄₀(NH₄)₂[(H₂O)<i>_n</i>⊂Mo₁₃₂O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]

Abstract

We describe the spontaneous self-assembly and the superstructure of a discrete surfactant-encapsulated cluster, (DODA)40(NH4)2[(H2O)n⊂Mo132O372(CH3COO)30(H2O)72] (2, n ≈ 50), which consists of a hollow giant isopolyoxomolybdate core covered by a hydrophobic shell of dimethyldioctadecylammonium (DODA) cations. The structural characterization of these nanoporous core−shell particles is based on small-angle X-ray scattering (SAXS) data on solutions of the encapsulated clusters, TEM investigations, FT-IR and UV−vis spectroscopy, as well as determination of the molecular area of 2 by Langmuir film investigations. Computer modeling of the solvent-accessible surface of the encapsulated cluster yields a central cavity with a volume of 1.5 nm3 that is occupied by approximately 50 H2O molecules. The cluster bears (Mo−O) 9-ring openings with an average diameter of 0.43 nm. The covered surface area of 84 Å2/DODA indicates a rather tight packing of the amphiphile at the cluster surface. Due to the unique supramolecular architecture of 2 as well as its high solubility in common organic solvents, this compound shows promising perspectives for future applications in host−guest chemistry and homogeneous size-selective catalysis.