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.