Trinuclear ruthenium core-containing polyoxometalate-based hybrids: preparation, characterization and catalytic behavior

Abstract

Two ruthenium-containing polyoxometalate-based hybrids (Ru-POMs), KH₈[Ru₃O(Trz)₆Cl₃]₂[(NaO₆)W₆(H₂O)₆(AsW₉O₃₃)₄]·28H₂O (1) and H₃[Ru₃O(Trz)₆Cl₃]₂[(WO)₂W(OH)(AsW₉O₃₃)₂]·6H₂O (2), (Trz = 1,2,4-triazole), were successfully isolated by a one-step hydrothermal method under different acidic conditions and further characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectroscopy, electrospray ionization and mass spectrometry (ESI-MS), thermogravimetric (TG) analyses and elemental analyses. Single-crystal X-ray diffraction analyses reveal two polyanions comprised of four/two identical trivacant Keggin-type polyanion building blocks, leading to the formation of tetrameric/dimeric assembly stabilized by additional metal–oxo cores, respectively. ESI-MS shows that the polyanion units [(NaO₆)W₆(H₂O)₆(AsW₉O₃₃)₄]¹¹⁻ and [(WO)₂W(OH)(AsW₉O₃₃)₂]⁵⁻ are intact in mixed solvent. Moreover, the two heterogeneous catalysts with trinuclear ruthenium cations were further investigated, and 1 was found to exhibit much higher yield (94.1%)/conversion (95.1%) and better selectivity (>99%) towards the oxidation of thioanisole to sulfoxide than 2.