Synthesis, crystal structure and characterizations of a new diphosphate Rb^sub 2^CaP^sub 2^O^sub 7

A new diphosphate Rb2CaP2O7 is synthesized by solid-states reaction. This compound crystallizes in the monoclinic space group of P21/n, with unit cell parameters of a=10.0238(9) Å, b=5.7861(5) Å, c=13.0654(ll) Å and β=104.726°. In this compound the [P2O7]4- dimers and [Ca06]10- units are interconnected by sharing the corner 0 atoms to form a 3D framework, with Rb+ cations filling in the interstices to balance the charge. The thermal property, IR and Raman spectra, UV-Vis-NIR diffuse reflectance spectrum and electronic band structure in Rb2CaP2O7 are determined, demonstrating its congruently melted characteristic and wide transparency down to the deep-ultraviolet region. Moreover, the replacement of Rb by K atoms in Rb2CaP2O7 can keep the compound structure unchanged, and the exemplified K1.85Rb0.15CaP2O7 exhibits almost the same fundamental physicochemical properties as Rb2CaP2O7.