Targeted Synthesis of Uranium(IV) Thiosilicates

Two new uranium(IV) thiosilicates, Cs₂Na₄[U₂(SiS₄)₂(Si₂S₈)] and Cs_2.12Na_3.88[U₂(SiS₄)₂(Si₂S₇)], were obtained by flux crystal growth using SiS₂ as a silicon source. The former compound contains a novel Si₂S₈^6- unit that features a terminal persulfide group. The magnetic susceptibility measurements performed on this compound revealed paramagnetic behavior with a moment of 3.49 μ_B per uranium atom as obtained from a Curie-Weiss law fit and showed no magnetic transition down to 2 K. The structures are based on closely related isomeric planar and 3D topologies that can be transformed into one another by a rotation of the structural units.

Ag5U(PS4)3: A Transition-Metal Actinide Phosphochalcogenide

The structure of Ag₅U(PS₄)₃ is unique, as in the literature there are no other structures of the type MAnPQ (M = transition metal, An = actinide, Q = S, Se, or Te). The compound has been synthesized at 1123 K by standard solid-state methods, and its single-crystal X-ray structure has been determined at 100(2) K. Ag₅U(PS₄)₃ crystallizes in a remarkable new structure type in space group P3₂21 of the trigonal system with three formula units in a hexagonal cell of dimensions a = b = 9.6635(2) Å, c = 17.1834(4) Å, and γ = 120°. In the structure, each U atom is coordinated to eight S atoms in a bicapped trigonal prismatic manner. Each P atom is tetrahedrally coordinated to four S atoms. Two of the three unique Ag atoms are connected to four S atoms in a distorted tetrahedral manner, whereas the third unique Ag atom forms an Ag₂S₆ species. The overall structure consists of U polyhedra connected to each other via PS₄ tetrahedra through edge-sharing in a zigzag fashion along the c axis to form infinite layers. PS₄ groups and the Ag atoms pack these layers. From density functional theory calculations, the total density of states of Ag₅U(PS₄)₃ is asymmetric with respect to spin and has finite spin polarization in the crystal cell: the magnetic moments of two of the U atoms are parallel, whereas the magnetic moment of the third U atom is antiparallel.

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)2(2–)] 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.