Embedding hexanuclear tantalum bromide cluster {Ta(6)Br(12)} into SiO(2) nanoparticles by reverse microemulsion method

Hexanuclear tantalum bromide cluster units [{Ta(6)Br(i)(12)}L(a)(6)] (i = inner, a = apical, L = ligand OH or H(2)O) are embedded into SiO(2) nanoparticles by a reverse microemulsion (RM) based method. [{Ta(6)Br(i)(12)}Br(a)(2) (H(2)O)(a)(4)]·nH(2)O (noted TBH) and tetraethyl orthosilicate (TEOS) are used as the starting cluster compound and the precursor of SiO(2), respectively. The RM system in this study consists of the n-heptane (oil phase), Brij L4 (surfactants), ethanol, TEOS, ammonia solution and TBH aqueous sol. The size and morphology of the product namely {Ta(6)Br(12)}@SiO(2) nanoparticles are analyzed by HAADF-STEM and EDS mappings. The presence and integrity of {Ta(6)Br(12)} in the SiO(2) nanoparticles are evidenced by EDS mapping, ICP-OES/IC and XPS analysis. The optical properties of {Ta(6)Br(12)}@SiO(2) nanoparticles are analyzed by diffuse reflectance UV-vis spectroscopy, further evidencing the integrity of the embedded {Ta(6)Br(12)} and revealing their oxidation state. Both {Ta(6)Br(12)}(2+) and {Ta(6)Br(12)}(3+) are found in SiO(2) nanoparticles, but the latter is much more stable than the former. The by-products in this RM-based synthesis, as well as their related factors, are also discussed.