Polynuclear tantalum(v) coordination complexes: from dinuclear {Ta2O} to octanuclear {Ta8O12} oxo species connected through aryl monotopic carboxylate linkers

Abstract

A series of monocarboxylic ligands (benzoic acid, 1-naphtoic acid, 2-naphtoic acid, antracene-9-carboxylic acid and 4′-methylbiphenyl-4-carboxylic acid) has been used to react upon mild heating with the pentavalent ethoxide tantalum(V) precursor Ta(OEt)₅ in isopropanol solvent. Five new molecular coordination compounds were isolated from crystallization upon cooling of the reactant's mixtures at room temperature. The different systems crystallized in dimeric {Ta₂O} (compound 1 and 2), tetrameric {Ta₄O₄} (compound 3 and 4) or octameric {Ta₈O₁₂} (compound 5) metal-oxo units stabilized by a combination of monocarboxylic ligands and isopropanolate solvent molecules. The five molecular samples were characterized in solid state by single-crystal and powder X-ray diffraction analyses, infrared spectroscopy, scanning electron microscopy (SEM) and thermogravimetric (TG) analysis. The chemical properties of compounds 1 & 5 have been tested for the catalytic conversion of dihydroxyacetone, showing Brønsted acidity.