Syntheses, crystal structures, and characterizations of three new pyrophosphates CsNaZnP2O7, RbNaZnP2O7, and RbLiMgP2O7

Three new pyrophosphates, CsNaZnP 2 O 7 , RbNaZnP 2 O 7 , and RbLiMgP 2 O 7 , were successfully obtained by the high-temperature solution method. The structures determined by single-crystal X-ray diffraction showed that the three compounds contained three-dimensional [Zn(P 2 O 7 ) 4/4 ] or [(Li 1/2 Mg 1/2 ) 2 (P 2 O 7 ) 4/4 ] frameworks, but they crystallized in different space groups, the monoclinic system P 2 1 / n for CsNaZnP 2 O 7 and RbNaZnP 2 O 7 , and the orthorhombic system Pnma for RbLiMgP 2 O 7 . All the compounds in the AA'MP 2 O 7 (A, A′ = different alkali metal ; M = Zn, Mg) family were summarized and compared. The thermal analyses and optical spectra analyses were performed on the title compounds. The band structures, density of states, and birefringence have also been investigated by the first-principles calculations.