Hydrothermal synthesis, structural and thermal characterizations of three open-framework gallium phosphites

Abstract Three new gallium phosphites A[Ga(HPO 3 ) 2 ], where A = K ( 1 ), NH 4 ( 2 ), Rb ( 3 ), have been synthesized by using mild hydrothermal conditions under autogeneous pressure. Their structures have been determined by single-crystal X-ray diffraction. These compounds crystallize in the hexagonal P 63 mc space group with a = 5.2567 (2) A and c = 12.2582 (3) A for 1 , a = 5.2576 (2) A and c = 12.9113 (4) A for 2 , a = 5.27020 (10) A and c = 12.7619 (5) A for 3 , with Z = 2 in the three phases. The three compounds are isostructural and exhibit the same framework topology, consisting of a layered structure stacked along the c-axis with the A + cations located in the interlayer spaces. The [Ga(HPO 3 ) 2 ] - sheets contain GaO 6 octahedra interconnected by phosphite units through sharing vertices. Thermal analysis under air atmosphere shows a large range stability for alkali cations containing compounds with decomposition starting around 750 K leading to phosphate phases. Under nitrogen, a disproportionation of the phosphite into red phosphorus and phosphates is expected, accompanied by a release of H 2 .