New group IIIA metal phosphate–oxalates containing dimethylammonium cations with proton conductivity

Abstract

Three new group IIIA metal phosphate–oxalate (MPO) compounds, namely [(CH₃)₂NH₂]₂[M₂(HPO₄)₂(H₂PO₄)₂(C₂O₄)] (M = Al (1), Ga (2)) and [(CH₃)₂NH₂]₂[In₂(HPO₄)₂(H₂PO₄)₂(C₂O₄)]·H₂O (3), have been synthesized. Their crystal structures feature an anionic layer with the sql topology net. In particular, 1 displays a proton conductivity (σ) of 9.09 × 10⁻³ S cm⁻¹ at 85 °C and under 98% relative humidity, which is the highest among MPOs. This study not only endows the main group metal-based MPO family with new members, but also contributes to further understanding of the structure-directing roles of amines and provides a feasible idea for improving the proton conductivity of MPOs.