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A new binary compound, NpSe2, possesses metal-chalcogen and chalcogen-chalcogen interactions different from those reported for other metal dichalcogenides. Its structure is incommensurately modulated and features linear Se chains and valence-ambiguous Np cations.

Single crystals of Ba6−2xU2+xAg4Se12 (x = 0 and 0.5) and Sr4Th2.78Cu4S12 were obtained by standard solid-state chemistry methods at 1173 K. The Ba6−2xU2+xAg4Se12 structures are modulated. They were solved and refined in the monoclinic C2(α0γ)0 super space group. The structure consists of layers formed by the connection of USe6 and AgSe4 polyhedra. The incommensurate nature of the structure arises from the disorder among Ba atoms and U atoms in the layers. The crystal structure of the Sr4Th2.78Cu4S12 was solved in space group Pmn21 of the orthorhombic system. The refinement of the structure reveals three partially occupied Th sites. The connection of ThS7 and CuS4 polyhedra form a channel structure filled by Sr atoms. From optical measurements Sr4Th2.78Cu4S12 is a semiconductor with an indirect band gap of 2.27(2) eV.

Standard solid-state methods produced black crystals of the compounds BaCu0.43(3)Te2 and BaAg0.77(1)Te2 at 1173 K; the crystal structures of each were established using single-crystal X-ray diffraction data. Both crystal structures are modulated. The compound BaCu0.43(3)Te2 crystallizes in the monoclinic superspace group P2(αβ1/2)0, having cell dimensions of a = 4.6406(5) A, b = 4.6596(5) A, c = 10.362(1) A, β = 90.000(9)°, and Z = 2 and an incommensurate vector of q = 0.3499(6)b* + 0.5c*. The compound BaAg0.77(1)Te2 crystallizes in the orthorhombic P21212(α00)000 superspace group with cell dimensions of a = 4.6734(1) A, b = 4.6468(1) A, c = 11.1376(3) A, and Z = 2 and an incommensurate vector of q = 0.364(2)a*. The asymmetric unit of the BaCu0.43(3)Te2 structure comprises eight crystallographically independent sites; that for BaAg0.77(1)Te2 comprises four. In these two structures, each of the M (M = Cu, Ag) atoms is connected to four Te atoms to make two-dimensional layers of [MxTe4/4]n- that are separated by layers of Ba atoms and square nets of Te. A Raman spectroscopic study at 298(2) K on a pelletized polycrystalline sample of BaAg0.8Te2 shows the presence of Ag-Te (83, 116, and 139 cm-1) and Ba-Te vibrations (667 and 732 cm-1). A UV-vis-NIR spectroscopic study on a powdered sample of BaAg0.8Te2 shows the semiconducting nature of the compound with a direct band gap of 1.0(2) eV, consistent with its black color. DFT calculations give a pseudo bandgap with a weak value of the DOS at the Fermi level.

Standard solid-state methods produced black crystals of the compounds BaCu

A new ternary telluride, Ba3ScTe5, with a pseudo-one-dimensional structure, was synthesized at 1173 K by standard solid-state methods. A single-crystal X-ray diffraction study at 100(2) K shows the structure to be modulated. The structure of the subcell of Ba3ScTe5 crystallizes with two formula units in the hexagonal space group D6h3-P63/mcm with unit cell dimensions of a = b = 10.1190(5) A and c = 6.8336(3) A. The asymmetric unit of the subcell structure consists of four crystallographically independent sites: Ba1 (site symmetry: m2m), Sc1 (-3.m), Te1 (m2m), and Te2 (3.2). Its structure is made up of chains of ∞1[ScTe33-] that are separated by Ba2+ cations. The Sc atoms are bonded to six Te1 atoms that form a slightly distorted octahedral geometry. The structure of the subcell also contains linear infinite chains of Te2 with intermediate Te···Te interactions. The superstructure of Ba3ScTe5 is incommensurate and was solved in the hexagonal superspace group P-6(00γ)0 with a = 10.1188(3) A and c = 6.8332(3) A and a modulation vector of q = 0.3718(2)c*. The arrangement and coordination geometries of the atoms in the superstructure are very similar to those in the substructure. However, the main difference is that the infinite chains of Te atoms in the superstructure are distorted owing to the formation of long- and short-bonded pairs of Te atoms. The presence of these chains with intermediate Te···Te interactions makes assignment of the formal oxidation states arbitrary. The optical absorption study of a polycrystalline sample of Ba3ScTe5 that was synthesized by the stoichiometric reaction of elements at 1173 K reveals a direct band gap of 1.1(2) eV. The temperature-dependent resistivity study of polycrystalline Ba3ScTe5 shows semiconducting behavior corroborating the optical studies, while density functional theory calculations report a pseudo band gap of 1.3 eV.

A new ternary telluride, Ba

Black single crystals of the Ba7UM2S12.5O0.5 (M = Ti, Si/Fe) compounds were obtained by standard solid-state chemistry method at 1123 K. Both compounds crystallize at 100 K in the Ba7UV2S12.5O0.5 structure type in space group I4/mcm of the tetragonal system with a = 16.1451(3) A and c = 9.5310(2) A (Ba7UTi2S12.5O0.5) and a = 16.1218(16) A and c = 9.4103(11) A (Ba7USi1.7Fe0.3S12.5O0.5). The crystal structures consist of infinite chains of U atoms octahedrally coordinated through the sharing of O/S corners along the c axis. The M atoms form isolated MS4 tetrahedra aligned also along the c axis. The space between US5O and MS4 polyhedra is filled by Ba atoms.

A new binary compound, NpSe

Single crystals and a polycrystalline sample of Ba

Single crystals and a polycrystalline sample of Ba2Ag2Se2(Se2) were synthesized by standard solid-state chemistry methods at 1173 and 973 K, respectively. The crystal structure of this ternary comp...

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) A, c = 17.1834(4) A, 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.

The black-colored compound BaUSe3 has been synthesized at 1173 K by a stoichiometric reaction of the elements in a CsCl flux. BaUSe3 crystallizes in the GdFeO3 structure type. There is no change in structure between 100 and 298 K. The U atoms in this structure are octahedrally connected to six Se atoms. Each octahedral unit shares all six corners with neighboring octahedra, forming a three-dimensional network. BaUSe3 can be charge balanced as Ba(2+)U(4+)(Se(2-))3. DFT electronic structure calculations found BaUSe3 to be antiferromagnetic in its ground state and to be a semiconductor with a band gap of 2.5 eV. The band gap is inconsistent with the black color of the material and with the small activation energy of 0.12(1) eV obtained from resistivity measurements. A UV-vis spectrum indicated that there was no band gap above 1 eV. It is possible that, for BaUSe3, intrinsic and extrinsic impurities from the flux create midgap states that lead to the experimentally measured narrow optical gap. More likely, BaUSe3 presents a challenge to DFT calculations as applied to 5f materials.

Single crystals of Ba2ZnQ3(Q= Se, Te) were obtained by solid-state reactions at 1173 K. These isostructural compounds crystallize in the K2AgI3structure type. The Zn atoms in this structure are coordinated to fourQatoms (2Q1, 1Q2, 1Q3) and these form a distorted tetrahedron around each Zn atom. Each ZnQ4tetrahedron shares two corners with neighboring ZnQ4tetrahedra resulting in the formation of infinite chains of [ZnQ44−] units. The absorption spectrum of a single crystal of Ba2ZnTe3shows an absorption edge at 2.10(2) eV, consistent with the dark-red color of the crystals. From DFT calculations Ba2ZnSe3and Ba2ZnTe3are found to be semiconductors with electronic band gaps of 2.6 and 1.9 eV, respectively.

The new ternary transition metal antimonide, Cu3Ru6Sb8, has been synthesized by a solid-state reaction of the elements at 1023 K. Its crystal structure has been established by single-crystal X-ray diffraction methods. It crystallizes in a new structure type in the trigonal crystal system (Pearson index hP17) in space group Pm1. The asymmetric unit of this structure contains six crystallographically independent sites: one Cu (site symmetry .2/m.), three Ru (Ru1 (.2/m.), Ru2 (3m.), and Ru3 (m.)), and two Sb sites (Sb1 (.m.) and Sb2 (3m.)). Two of the Ru atoms and the Cu atom are coordinated to six Sb atoms in a distorted octahedral fashion; the third Ru atom is found in a trigonal bipyramidal environment of five Sb atoms. The structure can be viewed as a hexagonal closed-packed array of Sb atoms, with Ru and Cu atoms in the interstices, representing a lattice that is an ordered variant of the NiAs structure. Electronic structure calculations provide insight into the chemical bonding in this transition metal antimonide. From magnetic and resistivity measurements on polycrystalline material, the compound is metallic and exhibits magnetic response that shows an effective moment smaller than any free-ion values, suggestive of weak itinerant magnetism.

The compound Cr4US8 has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P21/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6 octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr4US8 is complex. At temperatures above ~120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and χ(T) decreases monotonously with temperature, which is reminiscent of the Curie–Weiss law. At lower temperatures, the temperature dependence of χ(T) is complex and strongly dependent on the magnetic field strength.

International audience; The compound Ba3ThSe3(Se-2)(2) has been synthesized by solid-state methods at 1173 K. Its crystal structure features one-dimensional chains of (1)(infinity)[Th(Se)(3)(Se-2)(2)(6-)] separated by Ba2+ cations. Each Th atom in these chains is coordinated to two Se-Se single-bonded pairs and four Se atoms to give rise to a pseudooctahedral geometry around Th. The Th-Se distances are consistent with Th4+ and hence charge balance of Ba3ThSe3(Se-2)(2) is achieved as 3 x Ba2+, 1 x Th4+, 3 x Se2-, and 2 x Se-2(2-). From optical measurements the band gap of Ba3ThSe3(Se-2)(2) is 1.96(2) eV. DFT calculations indicate that the compound is a semiconductor.

Single crystals of K(Th0.75Sr0.25)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 × Q2–, 2 × (Q22.5–) has been proposed and hence a charge of −1.25 on Q of the “dichalcogenide”. Rather in K(Th0.75Sr0.25)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 Se22– pairs.

Single crystals of K(Th

A new quaternary uranium(V) selenide, Ba8PdU2Se12(Se2)2, has been synthesized by reaction of elements at 1173 K. A single-crystal X-ray diffraction study shows that the compound crystallizes in a new structure type with two formula units in space group D 2 h 12 – P n n m of the orthorhombic crystal system with cell constants of a=9.490(1), b=12.240(2), and c=13.780(3) A. Its crystal structure consists of PdU 2 Se 12 12 - units where U atoms are coordinated to six Se atoms in octahedral geometry and Pd atoms are coordinated to four Se atoms in square-planar geometry. These PdU 2 Se 12 12 - units are separated by Ba to result in a salt-like crystal structure. This compound also contains Se 2 2 - dimers that are part of Ba coordination polyhedra. The formula charge balances as (Ba2+)8(Pd2+)(U5+)2(Se2−)12( Se 2 2 - )2. Theoretical calculations predict antiferromagnetic semiconducting behavior for this compound with a band gap of 1.6 eV. Temperature-dependent four-probe resistivity measurements on single crystal confirm the semiconducting nature with an activation energy of 0.18(1) eV.

Five new quaternary chalcogenides of the 1113 family, namely BaAgTbS3, BaCuGdTe3, BaCuTbTe3, BaAgTbTe3, and CsAgUTe3, were synthesized by the reactions of the elements at 1173–1273 K. For CsAgUTe3 CsCl flux was used. Their crystal structures were determined by single-crystal X-ray diffraction studies. The sulfide BaAgTbS3 crystallizes in the BaAgErS3 structure type in the monoclinic space group C3,2h-C2/m, whereas the tellurides BaCuGdTe3, BaCuTbTe3, BaAgTbTe3, and CsAgUTe3 crystallize in the KCuZrS3 structure type in the orthorhombic space group D1,27,h-Cmcm. The BaAgTbS3 structure consists of edge-sharing [TbS69–] octahedra and [AgS59–] trigonal pyramids. The connectivity of these polyhedra creates channels that are occupied by Ba atoms. The telluride structure features 2∞[MLnTe32–] layers for BaCuGdTe3, BaCuTbTe3, BaAgTbTe3, and 2∞[AgUTe31–] layers for CsAgUTe3. These layers comprise [MTe4] tetrahedra and [LnTe6] or [UTe6] octahedra. Ba or Cs atoms separate these layers. As there are no short Q···Q (Q = S or Te) interactions these compounds achieve charge balance as Ba2+M+Ln3+(Q2–)3 (Q = S and Te) and Cs+Ag+U4+(Te2–)3.

Red plates of Cs5[U2(μ-S2)2Cl8]I were obtained in good yield from the reaction at 1173 K of U, GeI2 or SnI4, and S, with CsCl flux. The compound crystallizes in space group D2h25-Immm of the orthorhombic system in the Cs5[Nb2(μ-S2)2Cl8]Cl structure type. The centrosymmetric [U2(μ-S2)2Cl8]4– anion in the structure has mmm symmetry with the two U4+ atoms separated by 3.747(1) Å. Each U atom is coordinated to four Cl atoms and four S atoms from two S22– groups in a square-antiprismatic arrangement. The polarized absorbance spectra of Cs5[U2(μ-S2)2Cl8]I display prominent optical anisotropy. Magnetic measurements are consistent with the modified Curie–Weiss law at high temperatures. The low-temperature behavior may arise from antiferromagnetic coupling of the U4+ ions within the anion.

International audience; 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 D-4h(13)-P4(2)/mbc of the tetragonal system. Their structure features infinite one-dimensional chains of (1)(infinity)[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 Ak(2+)An(4+)(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 foe SrU(PS4)(2) and BaU(PS4)(2) using the Ha 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.

International audience; Six new uranium chalcogenides, Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, Ba3MnUS6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, related to the 2H hexagonal perovskite family have been synthesized by solid-state methods at 1173 K. These isostructural compounds crystallize in the K4CdCl6 structure type in space group D-3d(6) R3 (\₎c of the trigonal system with six formula units per cell. This structure type is remarkably flexible. The structures of Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 consist of infinite (1)(infinity)[MUQ(6) (6-)] chains (M = Fe or Mn; Q = S or Se) oriented along the c axis that are separated by Ba atoms. These chains are composed of alternating M-centered octahedra and U-centered trigonal prisms sharing triangular faces; in contrast, in the structures of Ba4USe6, Ba3.3Rb0.7US6, and Ba3.2K0.8US6, there are U-centered octahedra alternating with Ba-, Rb-, or K-centered trigonal prisms. Moreover, the Ba4USe6, Ba3FeUSe6, Ba3MnUSe6, and Ba3MnUS6 compounds contain U4+, whereas Ba3.3Rb0.7US6 and Ba3.2K0.8US6 are mixed U4+/5+ compounds. Resistivity and mu-Raman spectroscopic measurements and DFT calculations provide additional insight into these interesting subtle structural variations.

The mixed-cation compounds CsBa5Ti2Se9Cl and CsBa2Cl5 were synthesized in the same solid-state reaction at 1173 K. CsBa5Ti2Se9Cl adopts the Cs3CoCl5 structure type in the tetragonal crystal system whereas CsBa2Cl5 crystallizes in the PbU2Se5 structure type in the monoclinic crystal system. The CsBa5Ti2Se9Cl structure displays both Cs/Ba and Se/Cl disorder. From optical absorption measurements CsBa5Ti2Se9Cl is an indirect wide-gap semiconductor. From theoretical calculations CsBa2Cl5 has a large band gap of 6.4 eV.

Five compounds of the MAn2Q5 family, namely, SrU2S5, BaU2Se5, PbU2S5, BaTh2S5, and BaU2Te5, have been synthesized by high-temperature solid-state reactions. The crystal structures of these compounds were determined by single-crystal X-ray diffraction studies. SrU2S5, BaU2Se5, PbU2S5, and BaTh2S5 crystallize in the PbU2Se5 structure type in space group C2h5–P21/c of the monoclinic system, whereas BaU2Te5 adopts the (NH4)Pb2Br5 structure type in space group D4h18–I4/mcm of the tetragonal system. There are no Q–Q bonds in these structures, so the formulas charge balance as M2+(An4+)2(Q2–)5. The An atoms in the monoclinic structure are seven- or eight-coordinated by Q atoms; the U atoms in the tetragonal structure are eight-coordinated. The M atoms in the monoclinic structure are coordinated to either eight or nine Q atoms, depending on the monoclinic β angle; the M atoms in the tetragonal structure are 10-coordinated. Resistivity studies on single crystals of SrU2S5, BaU2Se5, and PbU2S5 show metallic behavio...

Black crystals of RbTiU₃Te₉ and CsTiU₃Te₉ have been synthesized at 1223 and 1173 K, respectively, by high-temperature solid-state routes. These compounds crystallize in a new structure type in space group C(2h)²-P2₁/m of the monoclinic system. The structure, which is similar to that of CsTiUTe₅, consists of UTe₂ layers connected into a three-dimensional framework by TiTe₆ octahedra. The expanded UTe₂ layers leave channels that are filled by Rb or Cs atoms. Single-crystal resistivity measurements on CsTiU₃Te₉ are consistent with semiconducting behavior; the calculated activation energy is 0.30(1) eV. X-ray photoelectron spectroscopic measurements on CsTiU₃Te₉ indicate that the compound contains U⁴⁺. From single-crystal magnetic measurements, CsTiU₃Te₉ is consistent with antiferromagnetic coupling between magnetic U atoms. The very low value of the effective magnetic moment of 0.56(2) μ(B) is believed to arise from a coexistence of magnetic and nonmagnetic U atoms.

The solid-state MU8Q17 compounds ScU8S17, CoU8S17, NiU8S17, TiU8Se17, VU8Se17, CrU8Se17, CoU8Se17, and NiU8Se17 were synthesized from the reactions of the elements at 1173 or 1123 K. These isostructural compounds crystallize in space group C2h3 - C2/m of the monoclinic system in the CrU8S17 structure type. X-ray absorption near-edge structure spectroscopic studies of ScU8S17 indicate that it contains Sc3+, and hence charge balance is achieved with a composition that includes U3+ as well as U4+. The other compounds charge balance with M2+ and U4+. Magnetic susceptibility measurements on ScU8S17 indicate antiferromagnetic couplings and a highly reduced effective magnetic moment. Ab Initio calculations find the compound to be metallic. Surprisingly, the Sc–S distances are actually longer than all the other M–S interactions, even though the ionic radii of Sc3+, low-spin Cr2+, and Ni2+ are similar.

The new compound U7O2Se12 was synthesized at 1173 K as a result of both unintentional and intentional oxygen contamination. The composition balances with formal charges of +4, –2, and –2 for U, O, and Se, respectively. U7O2Se12 crystallizes with one formula unit in space group C-P of the hexagonal system in a cell of dimensions a = 11.3222(4) A, c = 4.1362(1) A. The structure of U7O2Se12 closely resembles that of the An7Te12 (An = Th, U) compounds, but contains cavities, in which oxygen atoms are coordinated to three uranium atoms in a trigonal planar arrangement. It is not known if other members of the An7Q12 family (An = Th, U; Q = S, Se, Te) are actually An7O2Q12 compounds.

The three solid-state indium/germanium selenides Cs 4 In 8 GeSe 16 , CsInSe 2 , and CsInGeSe 4 have been synthesized at 1173 K. The structure of Cs 4 In 8 GeSe 16 is a three-dimensional framework whereas those of CsInSe 2 and CsInGeSe 4 comprise sheets separated by Cs cations. Both Cs 4 In 8 GeSe 16 and CsInGeSe 4 display In/Ge disorder. From optical absorption measurements these compounds have band gaps of 2.20 and 2.32 eV, respectively. All three compounds are charge balanced.

Powders of U6Fe30P19 and U6Co30P19 were synthesized through the use of tin fluxes. Examination of these powders at 298 K by the Guinier technique led to lattice parameters in the hexagonal system for U6Fe30P19 of a = 14.762(2) A, c = 3.6315(4) A, c/a = 0.2460, V = 685.3 A3 and for U6Co30P19 of a = 14.722(3) A, c = 3.6355(6) A, c/a = 0.2469, V = 682.4 A3. Single crystals of U6Fe30P19 were synthesized and its structure was determined. U6Fe30P19 crystallizes in the space group C1,3h – P of the hexagonal system in the Yb6Co30P19 structure type with one formula unit in a cell of dimensions determined at 100 K of a = 14.7206(4) A, c = 3.6243(1) A, c/a = 0.2462, V = 680.15(4) A3. The asymmetric unit of U6Fe30P19 comprises two U, ten Fe, and seven different P atoms. Each U atom is situated in a trigonal prism of six P atoms; each Fe atom is coordinated either by a tetrahedron or a square pyramid of P atoms. The distances are all less than 2.9 A. In addition, the structure contains numerous Fe–Fe bonds covering the range from 2.55 to 2.71 A. The proper space group of the Yb6Co30P19 structure type is discussed.

The compound Th2GeSe5 has been synthesized by the reaction of the elements at 1273 K. From a single-crystal study Th2GeSe5 crystallizes in the Ba5Si3 structure type with four formula units in the space group D84h−P4/ncc of the tetragonal system in a cell with dimensions a=7.4968(4) A and c=13.6302(9) A at 100(2) K. From optical absorption measurements Th2GeSe5 is found to have an optical band gap of 1.92 eV (indirect) or 1.98 eV (direct), consistent with its red color. Th2GeSe5 is a wide gap semiconductor, as indicated by its electrical resistivity at 298 K of 4.37(2)×109 Ω cm measured on a single crystal.

The compound Rb2Th7Se15 has been synthesized by the solid-state reaction at 1273 K of Th, Rb2Se3, Se, and Ge, and its structure has been determined by single-crystal X-ray diffraction methods. Red crystals of Rb2Th7Se15 crystallize at 100(2) K with four formula units in a new structure type in the monoclinic space group C 2 h 5 −P21/c. The structure is three-dimensional and comprises Rb and Th atoms coordinated by Se atoms to form nine-, eight-, and seven-coordinate polyhedra. Infinite channels that contain Rb atoms are present. Crystals of Rb2Th7Se15 are red in color; an indirect band gap of 1.83 eV was derived from single-crystal optical measurements.

Single crystals of Np2Se5 have been prepared through the reactions of Np and Se at 1223 K in an Sb2Se3 flux. The structure of Np2Se5, which has been characterized by single-crystal X-ray diffraction methods, crystallizes in the tetragonal space group P42/nmc. The crystallographic unit cell includes one unique Np and two Se positions. Se(1) atoms form one-dimensional infinite chains along the a and b axes with alternating intermediate Se-Se distances of 2.6489 (8) and 2.7999 (8) Å, whereas Se(2) is a discrete Se(2-) anion. Each Np is coordinated to 10 Se atoms and every NpSe10 polyhedron shares faces, edges, or vertices with 14 other identical metal polyhedra to form a complex three-dimensional structure. Np LIII-edge X-ray Absorption Near Edge Structure (XANES) measurements show a clear shift in edge position to higher energies for Np2Se5 compared to Np3Se5 (Np(3+)2Np(4+)Se(2-)5). Magnetic susceptibility measurements indicate that Np2Se5 undergoes a ferromagnetic-type ordering below 18(1) K. Above the transition temperature, Np2Se5 behaves as a paramagnet with an effective moment of 1.98(5) μB/Np, given by a best fit of susceptibilities to a modified Curie-Weiss law over the temperature range 50-320 K.

The compound Cs2U3Se7 has been synthesized at 1273 K by the reaction of U, Se, As, and Cs2Se3. The compound crystallizes in a new structure type in the orthorhombic space group D 2 h 16 – Pnma with four formula units in a cell of dimensions a = 22.847(1) A, b = 4.172(1) A, c = 16.639(1) A. In the asymmetric unit there are three independent U atoms, each octahedrally coordinated by six Se atoms. These USe6 octahedra are connected to form a channel structure with the channels running in the [010] direction. Within the unit cell the channel comprises twelve U centers.

A novel method involving a molten Ga flux for the synthesis of diffraction quality crystals of the compound Cu{sub 3.82(1)}Mo{sub 3}O{sub 12}, a copper molybdate in the Lyonsite (α-Cu{sub 3}Fe{sub 4}(VO{sub 4}){sub 6}) family, has been developed. Single-crystal X-ray diffraction data have been collected. Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} crystallizes in the space group P2{sub 1}2{sub 1}2{sub 1} with cell dimensions of a=4.9972(1) A, b=11.0259(3) A, and c=17.4912(5) A. Refinement of the resulting structure has enabled modeling of disorder in the channels of the structure and has indicated the localization of copper vacancies to these channel positions. Thermopower measurements indicate that Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} is a rare and interesting example of a cation-deficient n-type material. - Graphical abstract: The unit cell of Cu{sub 3.82(1)}(MoO{sub 4}){sub 3} with displacement ellipsoids drawn at the 75% probability level. Cu is green, Mo is blue, O is red. Highlights: ► A repeatable method for the synthesis Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} has been developed. ► Single crystals were formed from a polycrystalline sample through the use of a gallium flux. ► Thermopower measurements of Cu{sub 3.82(1)}Mo{sub 3}O{sub 12} show n-type behavior.

The barium uranium sulfides Ba 3.69 US 6 , BaUS 3 , and BaU 2 S 5 have been synthesized at 1273, 1323, and 1323 K, respectively. The structures of these compounds have been determined by single-crystal X-ray diffraction methods. They crystallize in space groups D 3 d 6 − R 3 ¯ c , D 2 h 16 − P n m a , and C 2 h 5 − P 2 1 / c , respectively. Among these three ternaries and Ba 2 US 6 the coordination geometries about the U atoms vary considerably. Ba 3.69 US 6 is a mixed U 4+ /U 5+ compound whereas the others are U 4+ compounds. The decreasing dimensionality of the four compounds with increasing Ba–to–U content shows the expected trend.

The compound Th(2)Se(5) has been synthesized and its structure determined by means of single-crystal X-ray diffraction methods. The subcell of Th(2)Se(5) is in the tetragonal space group P4(2)/nmc and is isostructural to Np(2)Se(5). The modulated structure of Th(2)Se(5) has been solved in the monoclinic super space group P2(α0γ)0. The structure features parallel infinite Se-Se chains with minimum and maximum Se-Se distances of 2.477(5) and 2.967(5) Å, respectively. Th(2)Se(5) is a semiconductor with an electrical resistivity that shows thermally activated Arrhenius behavior with an activation energy of 0.40(1) eV. From spectroscopic measurements, the band gap of Th(2)Se(5) is 0.37(2) eV. That the Th(2)Se(5) structure is modulated whereas the Np(2)Se(5) structure appears not to be implies that the formal oxidation state of Np in Np(2)Se(5) is 4+.

The compounds Ba2An(S2)2S2 (An = U, Th) have been synthesized by reactions of the elements with BaS and S at 1273 and 1173 K, respectively. These isostructural compounds crystallize in a new structure type in the tetragonal space group D(4h)(15)-P42/nmc. The structure comprises Ba2+ cations and (∞)(2)[An(S2)2(S)2(4–)] layers. The An4+ cations in these layers are arranged linearly and are bridged by S2– anions. Coordination about the An center, which has symmetry 4m2, consists of two S2(2–) ions and four S2– ions. Thus, the compounds are charge-balanced with An4+. No other alkali-metal actinide chalcogenides are known that contain chalcogen–chalcogen bonds. Optical measurements on Ba2Th(S2)2S2 indicate a direct band gap of 2.46(5) eV. Density functional theory calculations, performed with the HSE exchange-correlation potential, lead to band gaps of 2.2 and 1.8 eV for Ba2Th(S2)2S2 and Ba2U(S2)2S2, respectively, thus demonstrating the utility of applying this functional to 5f-electron systems.