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

Three new group IIIA metal phosphate-oxalate (MPO) compounds, namely [(CH 3 ) 2 NH 2 ] 2 [M 2 (HPO 4 ) 2 (H 2 PO 4 ) 2 (C 2 O 4 )] (M = Al (1), Ga (2)) and [(CH 3 ) 2 NH 2 ] 2 [In 2 (HPO 4 ) 2 (H 2 PO 4 ) 2 (C 2 O 4 )]·H 2 O (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.