Bottom-up synthesis of functionalized {Ce4(SiW9O34)2(l)2} polyoxometalates

Abstract

The reaction of Na₁₀[SiW₉O₃₄] with the 4f tetravalent cerium cation associated with four different organic O/N-donor ligands at pH = 4–4.5 gives rise to the formation of five anionic polyoxometalates [Ce₄(μ³-O)₂(SiW₉O₃₄)₂(C₄H₅O₄)₂]¹⁰⁻ (1), [Ce₄(μ³-O)₂(SiW₉O₃₄)₂(C₅H₇O₄)₂]¹⁰⁻ (2), [Ce₄(μ³-O)₂(SiW₉O₃₄)₂(C₅H₈O₂–NH₃)₂]⁸⁻ (3), [Ce₄(μ³-O)₂(SiW₉O₃₄)₂(C₆H₁₀O₂–NH₃)₂]⁸⁻ (4) and [(Ce₃(μ³-O)(μ²-OH)₃)(Ce₆(μ³-O)₄(μ³-OH)₄)(SiW₉O₃₄)₄]²¹⁻ (5). Compounds 1–4 consist of one tetranuclear Ce-based cluster fragment stabilized by two [SiW₉O₃₄]¹⁰⁻ polyanions and two organic linkers. Compound 5 is composed of a hexanuclear core combined with a trinuclear cerium core, stabilized by four [SiW₉O₃₄]¹⁰⁻ moieties. The molecular species were characterized by single-crystal and powder X-ray diffraction, IR spectroscopy, TGA, SEM/EDX, SAXS and ICP analysis. The solution stability of compounds 1–4 was also assessed by ²⁹Si and ¹⁸³W NMR.