A 3 Sr 2 P 7 O 21 (A = Rb, Cs): Two Polyphosphates Based on Different Types of P-O Chains and Ring Structures.

Two polyphosphates containing two types of polymerization of the [PO4 ] groups, Rb3 Sr2 P7 O21 and Cs3 Sr2 P7 O21 , were grown through a spontaneous nucleation method. Single-crystal X-ray diffraction data were collected in order to determine their structures. Interestingly, Rb3 Sr2 P7 O21 is the first example of two kinds of [PO3 ]∞ linear chains coexisting in one phosphate structure. However, in the structure of Cs3 Sr2 P7 O21 , the isolated [P4 O12 ] ring and the 1D [PO3 ]∞ chain can be observed, which is also rare in phosphates. After careful structural analysis, the alkali-metal cations have an effect on the polymerization of the [PO4 ] groups and make Rb3 Sr2 P7 O21 and Cs3 Sr2 P7 O21 crystallize in different space groups. What is more, IR spectra, UV-vis-NIR diffuse reflectance spectroscopy data, and first-principles theoretical calculations were adopted to determine the optical properties and the structure-properties relationship of the compounds.