Search

A two-dimensional array of polyoxomolybdate nanoball ([MoVI72MoV60O372(CH3COO)30(H2O)72]42-, Mo132) was successfully constructed by a Langmuir−Blodgett (LB) semiamphiphilic method by using Mo132 aqueous solution as a subphase and dimethyldioctadecylammonium (DODA) as a cationic amphiphile. Conservation of molecular structure of the Mo132 nanoball in the built-up LB film was confirmed by ultraviolet−visible (UV−vis) and infrared (IR) spectroscopy. Specular X-ray reflectivity (SXR) measurements combined with UV−vis spectroscopy revealed that the Mo132/DODA LB film had a well-defined layered structure containing a densely packed two-dimensional array of the Mo132 nanoballs. The electrochemical characteristics of the Mo132 nanoballs were retained after the deposition onto the solid substrates, which verifies that the LB semiamphiphilic method is an effective way to fabricate thin films composed of functional nanosized clusters toward a two-dimensional molecular device.

Microporous dodecahedral aggregates of a polyoxotungstate were synthesized by homogeneous precipitation from aqueous solution using hydrolysis of urea at 373 K (H3PW12O40 + 3/2(NH2)2CO + 3/2H2O → (NH4)3PW12O40↓ + 3/2CO2). The aggregates isolated after various reaction periods were characterized by several methods such as high-resolution scanning electron microscopy, N2 and Ar adsorption, X-ray and electron diffraction, and solid-state NMR. The formation process is also discussed. Each of these aggregates (0.3−5 μm in size) consisted of 5−10 nm nanocrystallites of (NH4)3PW12O40, which connected epitaxially (the same orientation of crystal planes), leaving pores between the nanocrystallites. With an increase in the reaction time, the initially formed spherical aggregates having micro- and mesopores gradually turned in to dodecahedral aggregates having only micropores and higher crystallinity. The dodecahedral aggregates obtained after 24 h were almost stoichiometric, (NH4)3PW12O40, according to 31P NMR, and...