A “missing” caesium member in the family of A 3Al2P3O12 aluminophosphates

Abstract A new caesium aluminophosphate, Cs 3 Al 2 P 3 O 12 , has been synthesized by spontaneous crystallization from the melt and structurally characterized. The compound crystallizes in the orthorhombic space group Pnma , with a =9.7675(2) Å, b =17.7537(3) Å, c =8.1063(2) Å, V =1405.71(2) Å 3 , and Z =4. Its crystal structure is based on an open interrupted framework built by alternating AlO 4 and PO 4 tetrahedra with Cs ions occupying the channels. The Cs 3 Al 2 P 3 O 12 framework topology resembles the previously known 4.8.12-net, which has been reported in the [C 4 N 3 H 16 ][Al 2 P 3 O 12 ] phase prepared by solvothermal synthesis in the presence of diethylenetriamine (DETA). The crystal chemical relationships between the K, Rb, Cs, Tl, [NH 4 ] and [C 4 N 3 H 16 ]-members of the A 3 Al 2 P 3 O 12 family of compounds are discussed.