Dimensional regulation in gigantic molybdenum blue wheels featuring {(W)Mo5} motifs for enhanced proton conductivity

Abstract

Dimensional regulation in polyoxometalates is an effective strategy during the design and synthesis of polyoxometalates-based high proton conductors, but it is not available to date. Herein, the precise regulation of dimensionality has been realized in an unprecedented gigantic molybdenum blue wheel family featuring pentagonal {(W)Mo₅} motifs through optimizing the molar ratio of Mo/W, including [Gd₂Mo₁₂₄W₁₄O₄₂₂(H₂O)₆₂]³⁸⁻ (0D-{Mo₁₂₄W₁₄}, 1), [Mo₁₂₆W₁₄O₄₄₁(H₂O)₅₁]⁷⁰⁻ (1D-{Mo₁₂₆W₁₄}_n, 2), and [Mo₁₂₄W₁₄O₄₃₀(H₂O)₅₀]⁶⁰⁻ (2D-{Mo₁₂₄W₁₄}_n, 3). Such important {(W)Mo₅} structural motif brings new reactivity into gigantic Mo blue wheels. There are different numbers and sites of {Mo₂} defects in each wheel-shaped monomer in 1–3, which leads to the monomers of 2 and 3 to form 1D and 2D architectures via Mo–O–Mo covalent bonds driven by {Mo₂}-mediated H₂O ligands substitution process, respectively, thus achieving the controllable dimensional regulation. As expected, the proton conductivity of 3 is 10 times higher than that of 1 and 1.7 times higher than that of 2. The continuous proton hopping sites in 2D network are responsible for the enhanced proton conductivity with lower activation energy. This study highlights that this dimensional regulation approach remains great potential in preparing polyoxometalates-based high proton conductive materials.