New quaternary alkali metal, rare earth (3+) thiophosphate, K2SmP2S7 with both [P2S6]4− and [PS4]3− anions

A new quaternary alkali metal, rare earth thiophosphate was synthesized by the ceramic method and characterized by single crystal X-ray diffraction: K2SmP2S7 crystallizes in the monoclinic space group C2 (no. 5) with the unit cell parameters a = 22.746(5) Å, b = 6.7362(13) Å, c = 8.9004(18) Å, β = 99.68(3)°, V = 1344.3(5) Å3 and Z = 2. The phase K2SmP2S7 can be better described as K4Sm2[PS4]2[P2S6] because it contains in the crystal structure both discrete anions [PS4]3− and [P2S6]4−. The crystal structure consists of infinite chains of 1∞[SmPS4] that are linked together through the ethane-like [P2S6]4− anions to form two-dimensional layers. The packing of K2SmP2S7 is formed by layers of 2∞[Sm2[PS4]2[P2S6]]4− separated by K+ cations. K2SmP2S7 was characterized by Raman and Fourier transform infrared (FTIR) spectroscopy and SEM-EDX microprobe analyses. The optical band gap of K2SmP2S7 was determined by UV–vis diffuse reflectance measurements to be 2.59 eV.