Dimeric four tartaric acid-bridged tetra-Zr-incorporated arsenotungstate showing decent proton conduction

Abstract

Exploring a new and robust material for proton conduction is of significant importance to the scientific interest and technological importance. Polyoxometalates (POMs) are a class of molecular anion metal oxide clusters with well-defined structures and diverse properties. Therefore, the design and synthesis of a POM-based material for proton conduction is extremely vital. Herein, a dimeric four tartaric acid-bridged tetra-Zr-incorporated arsenotungstate, [NH₂(CH₃)₂]₁₆KH₇[{Zr(tarH) O₂}₄{As₂W₁₉O₆₈}₂]·16H₂O (1) (tarH = tartaric acid), was successfully synthesized via a conventional aqueous method that utilized the tartaric acid ligand protection strategy, and it was systematically characterized by powder X-ray diffraction (PXRD), thermo gravimetric analysis (TGA), infrared (IR), ultraviolet (UV) spectra and energy-dispersive X-ray spectroscopy (EDS). This strategy included an innovative [Zr(tarH)WO₂]₄⁸⁺ core sandwiched by two distorted [As₂W₁₉O₆₈]¹⁶⁻ subunits. The [Zr(tarH)WO₂]₄⁸⁺ core is constituted of four Zr⁴⁺ and four {WO₂} groups, which are linked together by four tartaric acid ligands. Interestingly, the four tartaric acid ligands decorated on Zr⁴⁺ are covalently modified toward the W atoms. Moreover, the impedance measurements demonstrate that 1 has excellent proton conduction properties with the proton conductivity value of 3.82 × 10⁻³ S·cm⁻¹ under 348 K and 95% RH.

Graphical abstract