Syntheses, Crystal Structures, Optical and Theoretical Studies of the Actinide Thiophosphates SrU(PS4)2, BaU(PS4)2, and SrTh(PS4)2

Three new actinide thiophosphates, SrU­(PS4)2, BaU­(PS4)2, and SrTh­(PS4)2, have been synthesized by high-temperature solid-state methods, and their crystal structures were determined from single-crystal X-ray diffraction studies. These three isostructural compounds crystallize in a new structure type in space group D4h13-P42/mbc of the tetragonal system. Their structure features infinite one-dimensional chains of ∞1[An­(PS4)22–] anions (An = U or Th). Each An atom is coordinated by eight S atoms in a bicapped trigonal prism, and each P atom is tetrahedrally bonded to four S atoms. The compounds are readily charge balanced as Ak2+An4+(P5+(S2–)4)2. Optical studies on single crystals of SrU­(PS4)2 and BaU­(PS4)2 as well as ground single crystals of SrTh­(PS4)2 revealed a direct band gap of 2.13(2) eV and an indirect band gap value of 1.99(2) eV for SrU­(PS4)2 and a direct and indirect gap of about 2.28(2) eV for BaU­(PS4)2. SrTh­(PS4)2 has a relatively large band gap of 3.02(2) eV. DFT calculations for SrU­(PS4)2 and BaU­(PS4)2 using the HSE functional predict both compounds to be antiferromagnetic and have very similar electronic structures with band gaps of 2.7 eV. The band gap calculated for SrTh­(PS4)2 is 3.2 eV.