Construction of hydrothermally stable beryllium phosphite open-frameworks with high proton conductivity

Abstract

Two new beryllium phosphite anionic open-frameworks based on Be₃P₄O₁₂H₄ cluster building blocks, formulated as (Him)₂·Be₃(HPO₃)₄, were synthesized under solvothermal conditions, where im is imidazole. Interestingly, the use of different alcohols, i.e., isopropanol and n-propanol, as solvents afforded two new anionic open-frameworks with the same chemical composition, but different structures. Compound 1 crystallized in the monoclinic C2/c space group, whereas compound 2 crystallized in the triclinic P space group. Both compounds displayed intersected channels with 8-, 8-, 8-, and 12-membered windows along different directions. Considering Be₃P₄O₁₂H₄ clusters as four-connected nodes, both compounds showed a pcu topology. Notably, the frameworks of both open-frameworks remained stable after soaking in boiling water for one month. Furthermore, compound 1 exhibited a high proton conductivity of 2.03 × 10⁻³ S cm⁻¹ at 363 K and 98% relative humidity, indicating its potential as a hydrothermally stable proton-conducting material.