Na2Mg2P2O7F2: A new diphosphate of the cuspidine family without disorder designed by targeted structural modulation

A new alkali/alkali-earth metal pyrophosphate fluoride Na 2 Mg 2 P 2 O 7 F 2 without the structural disorder in the cuspidine family has been successfully prepared in the sealed system. Na 2 Mg 2 P 2 O 7 F 2 crystallizes in the space group P 2 1 / c (No. 14) of the monoclinic crystal system . The structure of Na 2 Mg 2 P 2 O 7 F 2 is shown to be an intricate three-dimensional (3D) framework that consists of the 2D layers [Mg 4 O 12 F 2 ] ∞ and the 1D chain [Na 2 O 8 F 3 ] ∞ interlinked by isolated P 2 O 7 groups, which demonstrates the precise coordination environment of cations and the framework in inorganic alkali/alkaline earth metal pyrophosphate fluoride. By comparing with other phosphate structures, we found that the introduction of F is conducive to the consistent arrangement of anionic group P 2 O 7 and enriches the diversity of cationic polyhedra. In addition, first-principle theoretical studies were also carried out to aid the understanding of microstructures, and Na 2 Mg 2 P 2 O 7 F 2 possesses a large band gap (7.1 eV) and has potential applications in the deep ultraviolet region.