A Rhombus-Like Tetrameric Vanadoniobate Containing Pseudo-Sandwich-Type {Li ⊂ V₂O₈(Nb₅O₁₄)₂} and Its Electrocatalytic Activity for the Selective Oxidation of Benzyl Alcohol

Ongoing research on V-containing polyoxoniobates (PONbs) is driven by their diverse structures and potential applications. Although Lindqvist-type {Nb₆O₁₉} is a widely used building block in PONbs, vanadoniobates based on {Nb₆O₁₉} and/or its derivatives are still very limited. Herein, a discrete vanadoniobate, LiNa₁₄K₁₁[Li₂ ⊂ V^IV₈Nb₃₂O₁₁₀]·45H₂O (1), has been synthesized by a hydrothermal method, which shows a rhombus-like tetrameric structure composed of two {V₂O₆(Nb₆O₁₉)} and two {Li ⊂ V₂O₈(Nb₅O₁₄)₂} subunits derived from {Nb₆O₁₉}. Notably, the {Li ⊂ V₂O₈(Nb₅O₁₄)₂} subunit has an interesting pseudo-sandwich-type structure, where a {LiV₂O₈} belt is coordinated by two monolacunary {Nb₅O₁₄} molecules and the central site of the cluster is occupied by Li⁺. Considering that 1 has both basic hexaniobates and redox active V centers, 1 was used as a noble metal-free electrocatalyst for the selective oxidation of benzyl alcohol to benzaldehyde, achieving complete conversion of benzyl alcohol with 94% selectivity for benzaldehyde in 3 h under ambient conditions without using any alkaline additives. Moreover, the catalytic performance of 1 remained largely unchanged after four cycles.