Positional flexibility: syntheses and characterization of six uranium chalcogenides related to the 2H hexagonal perovskite family

Synthesis, Characterization, and Magnetic Properties of Uranium-Containing 2H-Perovskite-Related Sulfides: Ba3MUS6 (M = Mn, Fe, Co, Ni) and Ba3Co0.858(5)Mg0.142(5)US6

The uranium-containing 2H-perovskite-related chalcogenide family of compounds was revisited using the recently developed boron-chalcogen mixture (BCM) method for actinides to aid in their syntheses and to obtain magnetic measurements. Two known 2H-perovskite-related structures, Ba3MnUS6 and Ba3FeUS6, were synthesized using the BCM method and were found to exhibit antiferromagnetic transitions at TN = ∼7.6 and 10.8 K, respectively. Combining the BCM method with the molten flux crystal growth technique resulted in single crystals of three new compositions, Ba3NiUS6, Ba3CoUS6, and Ba3Co0.858(5)Mg0.142(5)US6, the synthesis and characterization of which is reported. Magnetic measurements of Ba3NiUS6 revealed a complex magnetic susceptibility consisting of a weak, glassy, antiferromagnetic transition near 65 K followed by an antiferromagnetic transition at TN = ∼18 K. A reduced radius ratio plot for the existing chalcogenide compositions and new additions to this structure type reported herein is presented to aid in the search for additional 2H-perovskite-related sulfides.

Transuranium Sulfide via the Boron Chalcogen Mixture Method and Reversible Water Uptake in the NaCuTS3 Family

The behavior of 5f electrons in soft ligand environments makes actinides, and especially transuranium chalcogenides, an intriguing class of materials for fundamental studies. Due to the affinity of actinides for oxygen, however, it is a challenge to synthesize actinide chalcogenides using non-metallic reagents. Using the boron chalcogen mixture method, we achieved the synthesis of the transuranium sulfide NaCuNpS₃ starting from the oxide reagent, NpO₂. Via the same synthetic route, the isostructural composition of NaCuUS₃ was synthesized and the material contrasted with NaCuNpS₃. Single crystals of the U-analogue, NaCuUS₃, were found to undergo an unexpected reversible hydration process to form NaCuUS₃·xH₂O (x ≈ 1.5). A large combination of techniques was used to fully characterize the structure, hydration process, and electronic structures, specifically a combination of single crystal, powder, high temperature powder X-ray diffraction, extended X-ray absorption fine structure, infrared, and inductively coupled plasma spectroscopies, thermogravimetric analysis, and density functional theory calculations. The outcome of these analyses enabled us to determine the composition of NaCuUS₃·xH₂O and obtain a structural model that demonstrated the retention of the local structure within the [CuUS₃]^- layers throughout the hydration-dehydration process. Band structure, density of states, and Bader charge calculations for NaCuUS₃, NaCuUS₃·xH₂O, and NaCuNpS₃ along with X-ray absorption near edge structure, UV-vis-NIR, and work function measurements on ACuUS₃ (A = Na, K, and Rb) and NaCuUS₃·xH₂O samples were carried out to demonstrate that electronic properties arise from the [CuTS₃]^- layers and show surprisingly little dependence on the interlayer distance.

Structures and Magnetic Properties of K2Pd4U6S17, K2Pt4U6S17, Rb2Pt4U6S17, and Cs2Pt4U6S17 Synthesized Using the Boron-Chalcogen Mixture Method

A series of A₂M₄U₆S₁₇ (A = alkali metal; M = Pd, Pt) compounds, specifically K₂Pd₄U₆S₁₇, K₂Pt₄U₆S₁₇, Rb₂Pt₄U₆S₁₇, and Cs₂Pt₄U₆S₁₇, were synthesized using the combined boron-chalcogen mixture and molten flux crystal growth methods. The formation of rubidium- and cesium-containing analogues resulted from a in situ alkali polysulfide flux formed from alkali carbonates. The successful synthesis of single crystals of the title compounds allowed for their structural characterization by single-crystal X-ray diffraction. The structure determination revealed disorder of the alkali cations in Rb₂Pt₄U₆S₁₇ and Cs₂Pt₄U₆S₁₇, while the potassium cations in K₂Pd₄U₆S₁₇ and K₂Pt₄U₆S₁₇ were fully ordered. Magnetic measurements were performed on samples of K₂Pt₄U₆S₁₇, Rb₂Pt₄U₆S₁₇, and Cs₂Pt₄U₆S₁₇ that contained small amounts of paramagnetic β-US₂ and diamagnetic PtS. Antiferromagnetic order was observed at T_N = 9.1 K for K₂Pt₄U₆S₁₇. No long-range magnetic order was observed for Rb₂Pt₄U₆S₁₇ and Cs₂Pt₄U₆S₁₇. Uranium moments of 2.5, 2.6, and 2.6 μ_B were measured for K₂Pt₄U₆S₁₇, Rb₂Pt₄U₆S₁₇, and Cs₂Pt₄U₆S₁₇, respectively.

Lanthanide thioborates, an emerging class of nonlinear optical materials, efficiently synthesized using the boron–chalcogen mixture method

Single crystals of LnBS3 (Ln = La–Nd) were synthesized by the combined boron–chalcogen mixture and molten flux growth methods. SHG measurements confirmed the expectation that LaBS3 would exhibit a strong SHG response, measured at 1.5 × KDP.

Five coordinated Mn in Ba4Mn2Si2Te9: synthesis, crystal structure, physical properties, and electronic structure

A new structure type Ba4Mn2Si2Te9 containing unique MnTe5 units is synthesized. The structure comprises two independent Mn atoms, each with 50% occupancy. It is a narrow bandgap semiconductor (Eg = 0.6(1) eV) consistent with the DFT studies.

K(Th0.75Sr0.25)2Se6: Structural Change Resulting from the Disorder of Differently Charged Cations

Single crystals of K(Th_0.75Sr_0.25)₂Se₆ were obtained by a standard solid-state chemistry route at 1173 K. This compound does not belong to the AAn₂Q₆ family (A = K, Rb, Cs, or Tl; An = Th, U, or Np; Q = S, Se, or Te) that possesses infinite Q-Q-Q chains and where a charge distribution of A⁺, 2 × An⁴⁺, 2 × Q^2-, 2 × (Q₂^2.5-) has been proposed and hence a charge of -1.25 on Q of the "dichalcogenide". Rather in K(Th_0.75Sr_0.25)₂Se₆, where the Th and Sr cations randomly occupy the same site, incorporation of these differently charged cations breaks the infinite Se-Se-Se chains into a structure that has typical Se₂^2- pairs.

Tetrametallic Thorium Compounds with Th4E4 (E = S, Se) Cubane Cores

Tetrametallic thorium compounds with a Th₄E₄ core (E = S, Se) having a distorted cubane structure can be prepared by ligand-based reductions of elemental E with thorium chalcogenolates, prepared by in situ oxidation of Th metal with a 3:1 mixture of PhEEPh and F₅C₆EEC₆F₅. Four compounds, (py)₈Th₄S₄(μ₂-SPh)₄(SC₆F₅)₄, (py)₈Th₄S₄(μ₂-SPh)₄(SeC₆F₅)₄, (py)₈Th₄Se₄(μ₂-SePh)₄(SeC₆F₅)₄, and (py)₈Th₄Se₄(μ₂-SePh)₄(SC₆F₅)₄, were isolated and characterized by NMR spectroscopy and X-ray diffraction. These compounds clearly demonstrate the chemical impact of ring fluorination, with the less-nucleophilic EC₆F₅ ligands occupying the terminal binding sites and the EPh ligands bridging two metal centers. For this series of compounds, crystal packing and intermolecular π···π and H-bonding interactions result in a consistent motif and crystallization in a body-centered tetragonal unit cell. Solution-state ⁷⁷Se NMR spectroscopy reveals that the solid-state structures are maintained in pyridine.

Overview of the crystal chemistry of the actinide chalcogenides: incorporation of the alkaline-earth elements

This review focuses on the results of exploratory syntheses of alkaline-earth-metal actinide chalcogenides Ak–An–Q (Ak = Ba, Sr; An = Th, U; Q = S, Se, and Te). About thirty new compounds and eleven new structure types are described.