Phosphates with Two Types of Isolated P-O Groups: Noncentrosymmetric Na 6 Sr 2 Bi 3 (PO 4 )(P 2 O 7 ) 4 and Centrosymmetric Cs 2 CaBi 2 (PO 4 ) 2 (P 2 O 7 ).

Inorganic phosphates are of great interest, because of their rich structural chemistry and multiple functional properties. Compared with the phosphates that only contain the solely condensed P-O groups, the phosphates with various condensed P-O groups are less reported, especially for the noncentrosymmetric (NCS) ones. Here, two new bismuth phosphates, Na 6 Sr 2 Bi 3 (PO 4 )(P 2 O 7 ) 4 and Cs 2 CaBi 2 (PO 4 ) 2 (P 2 O 7 ), were synthesized by the solid-state reaction and both structures contain two types of isolated P-O groups. Remarkably, Na 6 Sr 2 Bi 3 (PO 4 )(P 2 O 7 ) 4 crystallizes in the tetragonal space group P 4̅2 1 c , which represents the first NCS bismuth phosphate with PO 4 and P 2 O 7 groups. Detailed structural comparisons among Bi 3+ -containing alkali/alkaline-earth metal phosphates show that the ratios of cations/phosphorus profoundly influence the condensed degree of P-O groups. Ultraviolet-visible-near-infrared (UV-vis-NIR) diffusion spectra show that both compounds have the relatively short UV cutoff edges. And Na 6 Sr 2 Bi 3 (PO 4 )(P 2 O 7 ) 4 has a second-harmonic generation response of 1.1 × KDP. The first-principles calculations are carried out to understand the structure-performance relationship.