Two New Isopolyoxovanadates Based on V10 and V6: Structural Assembly and Dual Catalytic Applications

Abstract

Two novel isopolyoxovanadates modified by ethylenediamine, [Cu(en)2]2[VIV4VV6O25] (1) and [Cu(en)2][VV6O16] (2) (en=ethanediamine, C2H8N2), have been successfully synthesized under hydrothermal conditions. Both compounds represent new structural types in the V10 and V6 clusters family, featuring two-dimensional pure inorganic vanadate layer structures. The compounds were thoroughly characterized by infrared spectroscopy (IR), single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TG). Their catalytic properties were investigated in sulfide oxidation and Knoevenagel condensation under mild conditions. Notably, compound 1, which contains mixed-valent VIV/VV centers, demonstrates exceptional catalytic performance in the selective oxidation of methyl phenyl sulfide. It achieves a conversion rate of 98.3% with a selectivity of 84.9% towards sulfoxide within just 30 minutes at room temperature. Moreover, in the Knoevenagel condensation, compound 1 demonstrates remarkable activity with 95.2% conversion of benzaldehyde and >99% product selectivity within 90 minutes. Recycling experiments confirm the excellent stability of both compounds. This study not only enhances the structural diversity of polyoxovanadates but also offers efficient bifunctional catalysts for organic transformations under mild conditions.