New quaternary alkali metal, rare earth (3+) thiophosphate, K_2SmP_2S_7 with both [P_2S_6]~(4-) and [PS_4]~(3-) anions

摘要

A new quaternary alkali metal, rare earth thiophosphate was synthesized by the ceramic method and characterized by single crystal X-ray diffraction: K_2SmP_2S_7 crystallizes in the monoclinic space group C2 (no. 5) with the unit cell parameters a - 22.746(5) A, b = 6.7362(13) A, c = 8.9004(18) A, β = 99.68(3)°, V= 1344.3(5) A~3 and Z= 2. The phase K_2SmP_2S_7 can be better described as K_4Sm_2[PS_4]_2[P_2S_6] because it contains in the crystal structure both discrete anions [PS_4]~(3-) and [P_2S_6]~(4-). The crystal structure consists of infinite chains of _∞~1[SmPS_4] that are linked together through the ethane-like [P_2S_6]~(4-) anions to form two-dimensional layers. The packing of K_2SmP_2S_7 is formed by layers of _∞~2[Sm_2[PS_4]_2[P_2S_6]~(4-) separated by K~+ cations. K_2SmP_2S_7 was characterized by Raman and Fourier transform infrared (FTIR) spectroscopy and SEM-EDX microprobe analyses. The optical band gap of K_2SmP_2S_7 was determined by UV-vis diffuse reflectance measurements to be 2.59 eV.