Syntheses, characterization and theoretical calculation of the first alkali magnesium pyrophosphate fluorides with a short cutoff edge

Two new alkali/alkaline-earth metal pyrophosphate fluorides, A 2 Mg 2 P 2 O 7 F 2 ( A  = K , Rb) have been synthesized, structurally analyzed, and characterized for the first time. They both crystallize in the Pbcn space group and show similar crystal structures. Their structures contain 1 [M g 2 O 7 F 3 ] ∞ chains made up of edge-sharing MgO 4 F 2 octahedra and 2 [ A 2 O 11 F 4 ] ∞ layers built by face-sharing [ A 2 O 11 F 4 ] clusters, which are bridged by isolated P 2 O 7 units to construct a 3D framework. It's worth noting that A 2 Mg 2 P 2 O 7 F 2 ( A  = K , Rb) are the first pyrophosphate fluoride in the A -Mg-P-O-F ( A  = alkali metal) system. Furthermore, the optical measurements of the title compounds show that they all possess UV absorption cutoff edges. First-principles theoretical studies were conducted to understand the electronic structures.