Synthesis, structure and characterization of three new Mg-containing phosphates with deep-UV cut-off edges

Three new Mg-containing phosphates, AMg(2)P(3)O(10) (A = Li, Cs) and Rb2MgP2O7, have been successfully synthesized using a high-temperature solution method. Single-crystal X-ray diffraction measurements show that they crystallize in different space groups, P21/m for LiMg2P3O10, Pbcn for CsMg2P3O10 and Pnma for Rb2MgP2O7. Interestingly, their structures contain two different types of P-O connection modes, i.e., P3O10 trimers in AMg(2)P(3)O(10) (A = Li, Cs) and P2O7 dimers in Rb2MgP2O7. Correspondingly, the Mg2+-centered polyhedra also exhibit three different polymerizations, including one-dimensional (1D) [MgO6](infinity) infinite chains in LiMg2P3O10, Mg2O8 dimers in CsMg2P3O10 and isolated MgO5 square pyramids in Rb2MgP2O7. Detailed structural analysis indicates that the different sizes of the A-site cations and flexible coordination of Mg2+ cations are responsible for the structural differences. Furthermore, optical measurements of the three compounds show that they all possess deep-UV absorption cut-off edges (<190 nm). Their thermal properties and bond valence sum difference map (BVS-DM) calculations were also studied.