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 ⊂ VIV8Nb32O110]·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.