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The system IrX(CO)[P(C(6)H(5))(3)](2) in benzene solution adds mo lecular oxygen reversibly if X is chlorine and irreversibly if X is iodine. The crystal structure of the complex IrIO(2)(CO)[P(C(6)H(5))(3)](2) * CH(2)Cl(2) is reported here and compared with a previous study of the structure of IrClO(2)(CO)[P(C(6)H(5))(3)](2). The O-O bond length is 1.47 +/- 0.02 angstroms in the irreversibly oxygenated iodo-compound and 1.30 +/- 0.03 angstroms in the reversibly oxygenated chloro compound.

Standard solid-state methods produced black crystals of the compounds BaCu 0.43(3) Te 2 and BaAg 0.77(1) Te 2 at 1173 K; the crystal structures of each were established using single-crystal X-ray diffraction data. Both crystal structures are modulated. The compound BaCu 0.43(3) Te 2 crystallizes in the monoclinic superspace group P 2( αβ 1/2)0, having cell dimensions of a = 4.6406(5) Å, b = 4.6596(5) Å, c = 10.362(1) Å, β = 90.000(9)°, and Z = 2 and an incommensurate vector of q = 0.3499(6) b * + 0.5 c *. The compound BaAg 0.77(1) Te 2 crystallizes in the orthorhombic P 2 1 2 1 2(α00)000 superspace group with cell dimensions of a = 4.6734(1) Å, b = 4.6468(1) Å, c = 11.1376(3) Å, and Z = 2 and an incommensurate vector of q = 0.364(2) a *. The asymmetric unit of the BaCu 0.43(3) Te 2 structure comprises eight crystallographically independent sites; that for BaAg 0.77(1) Te 2 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 [M x Te 4/4 ] 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 BaAg 0.8 Te 2 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 BaAg 0.8 Te 2 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.

A new ternary telluride, Ba 3 ScTe 5 , 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 Ba 3 ScTe 5 crystallizes with two formula units in the hexagonal space group D 6 h 3 - P 6 3 / mcm with unit cell dimensions of a = b = 10.1190(5) Å and c = 6.8336(3) Å. The asymmetric unit of the subcell structure consists of four crystallographically independent sites: Ba1 (site symmetry: m 2 m ), Sc1 (-3. m ), Te1 ( m 2 m ), and Te2 (3.2). Its structure is made up of chains of ∞ 1 [ScTe 3 3- ] that are separated by Ba 2+ 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 Ba 3 ScTe 5 is incommensurate and was solved in the hexagonal superspace group P -6(00γ)0 with a = 10.1188(3) Å and c = 6.8332(3) Å 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 Ba 3 ScTe 5 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 Ba 3 ScTe 5 shows semiconducting behavior corroborating the optical studies, while density functional theory calculations report a pseudo band gap of 1.3 eV.

A new binary compound, NpSe 2, 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., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Single crystals and a polycrystalline sample of Ba 2 Ag 2 Se 2 (Se 2 ) were synthesized by standard solid-state chemistry methods at 1173 and 973 K, respectively. The crystal structure of this ternary compound was established by single-crystal X-ray diffraction studies at 100(2) K. The superstructure of this compound is commensurate and crystallizes in the space group P2 1 / c of a monoclinic system with cell constants of a = 6.1766(2) Å, b = 6.1788(2) Å, c = 21.5784(8) Å, and β = 90.02(1)° ( Z = 4). The asymmetric unit of the superstructure comprises eight atoms occupying general positions: two Ba atoms, two Ag atoms, and four Se atoms. In this structure, each Ag atom is tetrahedrally coordinated with four adjacent Se atoms to form distorted AgSe 4 units that share edges with the neighboring tetrahedra to form a two-dimensional [AgSe 4/4 ] - layer. These layers are separated by Ba 2+ and Se 2 2- units. The presence of the Se 2 2- unit is also supported by an intense band at around 247 cm -1 in the Raman spectrum of Ba 2 Ag 2 Se 2 (Se 2 ). A density functional theory study shows that the compound is a semiconductor with a calculated band gap of 1.1 eV. As determined by UV-visible spectroscopy, the direct and indirect band gaps are 1.23(2) and 1.10(2) eV, respectively, in good agreement with the theory and consistent with the black color of the compound. A temperature-dependent resistivity study also confirms the semiconducting nature of Ba 2 Ag 2 Se 2 (Se 2 ).

The structure of Ag 5 U(PS 4 ) 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. Ag 5 U(PS 4 ) 3 crystallizes in a remarkable new structure type in space group P3 2 21 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 Ag 2 S 6 species. The overall structure consists of U polyhedra connected to each other via PS 4 tetrahedra through edge-sharing in a zigzag fashion along the c axis to form infinite layers. PS 4 groups and the Ag atoms pack these layers. From density functional theory calculations, the total density of states of Ag 5 U(PS 4 ) 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.

Single crystals of K(Th 0.75 Sr 0.25 ) 2 Se 6 were obtained by a standard solid-state chemistry route at 1173 K. This compound does not belong to the AAn 2 Q 6 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 × An 4+ , 2 × Q 2- , 2 × (Q 2 2.5- ) has been proposed and hence a charge of -1.25 on Q of the "dichalcogenide". Rather in K(Th 0.75 Sr 0.25 ) 2 Se 6 , 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 Se 2 2- pairs.

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 are described. Although the basic building blocks of their structures are usually AnQ 6 octahedra and AkQ 8 bicapped trigonal prisms, these are combined in diverse ways to afford eleven new structure types. The structures reconfirm the prevailing presence of An 4+ in chalcogenides, although some of the compounds discovered are mixed An 4+ /An 5+ systems, and a few contain only An 5+ . The tendency of the chalcogens to form Q-Q bonds is again evident from the presence of S-S single bonds and infinite Te-Te-Te linear chains. The latter possess interatomic distances of lengths greater than that of a Te-Te single bond but less than that of a Te-Te van der Waals interaction. Assignment of formal oxidation states in compounds containing these chains is arbitrary at best. Addition of metal atoms (M) affords quaternary structures, some of which show remarkable flexibility in the positions of the An and M atoms, and in such compounds the nature of the M elements influences directly the dimensionality of the resultant structure. The presence of adventitious oxygen, often from etching of the fused-silica tubes by oxyphilic An elements, results in new quintary compounds that show remarkable structural variations with change of M. The compounds discussed have shown transport and electronic structures that range from metallic-like to semiconducting. We find, with the exception of BaUSe 3 , when comparisons can be made that the values of the calculated band gaps are reasonably close but usually lower than the experimentally derived values. Thus the method used, in particular the HSE functional, has been generally successful on these 5f actinides. This is an important result because in the absence of suitable crystals, and hence experimental measurements, it still may be possible to offer credible predictions of some of the magnetic and electronic properties of the compounds.

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.

Four new actinide chalcogenides—namely, Ba2Cu4USe6, Ba2Cu2ThSe5, Ba2Cu2USe5, and Sr2Cu2US5—were synthesized via solid-state methods at 1173 K. Single-crystal X-ray diffraction studies show that Ba2Cu4USe6 crystallizes in a new structure type in space group C2h5–P21/c of the monoclinic system, whereas the three other compounds are isostructural and adopt the Ba2Cu2US5 structure type in space group C2h3–C2/m, also of the monoclinic system. These Ak/Cu/An/Q structures (Ak = alkaline-earth metal; An = actinide; Q = chalcogen) have no short Q–Q interactions and, hence, are charge-balanced with Ak2+, Cu1+, An4+, and Q2–. Crystal structures of all these compounds are two-dimensional and feature layers that are separated by Ba2+ cations. The compositions of these layers differ. In the structure of Ba2Cu4USe6, the ∞2[Cu4USe64–] layers comprising USe6 octahedra and CuSe4 tetrahedra stack perpendicular to the a-axis. These ∞2[Cu4USe64–] layers show short Cu–Cu interactions. In the three isostructural Ak2Cu2AnQ5 compounds, AnQ6 octahedra and CuQ4 tetrahedra are connected along the c-axis in the sequence “...oct tet tet oct tet tet...” to form the ∞2[Cu2AnQ54–] layers. Resistivity, optical, and DFT calculations show semiconducting behavior for these compounds.

The three new quaternary actinide chalcogenides Ba2TiUTe7, Ba2CrUTe7, and Ba2CrThTe7 have been synthesized. From single-crystal X-ray diffraction studies these isostructural compounds are found to crystallize in a new structure type in space group D2h16–Pnma of the orthorhombic system. The structure features ∞1[MAnTe74–] strips (M = Cr or Ti; An = Th or U) that propagate in the b-direction and are separated by Ba cations. An atoms are coordinated to eight Te atoms in a bicapped trigonal-prismatic geometry while M atoms are octahedrally coordinated to six Te atoms. Sharing of the AnTe8 and MTe6 polyhedra forms ∞1[MAnTe74–] strips. The presence of the infinite linear Te–Te–Te chains in these compounds makes assignment of oxidation states arbitrary. Resistivity measurements and DFT calculations provide further insight into the properties of these compounds.

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.

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.

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 D3d6–R3̅c 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[MUQ66–] 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 μ-Raman spectroscopic measurements and DFT calculations provide additional insight into these interesting subtle structural variations.

Single crystals of ScUS3 were synthesized in high yield in a single step at 1173 K. ScUS3 crystallizes in the FeUS3 structure type in the space group D2h(17)–Cmcm of the orthorhombic system with four formula units in a cell of dimensions a = 3.7500(8) Å, b = 12.110(2) Å, and c = 9.180(2) Å. Its structure consists of edge- and corner-sharing ScS6 octahedra that form two-dimensional layers. U atoms between layers are connected to eight S atoms in a bicapped trigonal-prismatic fashion. ScUS3 can be easily charge-balanced as Sc(3+)U(3+)(S(2–))3 as there are no S–S single bonds present in the crystal structure. High temperature-dependent resistivity measurements on a single crystal of ScUS3 show semiconducting behavior with an activation energy of 0.09(1) eV. A magnetic study on powdered single crystals of ScUS3 reveals an antiferromagnetic transition at 198 K followed by a ferromagnetic transition at 75 K. The weak ferromagnetic behavior at low temperature may originate from canted antiferromagnetic spins. A density functional theory (DFT) calculation predicts ScUS3 to be ferromagnetic and either a very poor metal or a semiconductor with a very small gap.

The three new solid-state compounds BaThTe4, BaUTe4, and BaUTe6 have been synthesized and characterized. BaThTe4 and BaUTe4 are isostructural. The structure consists of infinite ∞(2)[AnTe4(2–)] layers separated by Ba(2+) ions. Each An (An = Th, U) atom is coordinated to eight Te atoms in a bicapped trigonal-prismatic arrangement. Te atoms are connected to each other to form linear infinite chains. These Te–Te interactions are longer than that of a Te–Te single bond. However, this structure also possesses Te–Te single bonds. Charge balance in the formula BaAnTe4 may be achieved with [Ba(2+)]2[(An(4+))2(Te(2–))2(Te2(2–))(Te2(3–))2](4–). The structure of BaUTe6 features one-dimensional anionic ∞(1)[UTe6(2–)] chains that are separated by Ba(2+) ions. There are three Te–Te single bonds around each U atom. The anion in this structure can thus be described as [U(4+)(Te2(2–))3](2–). Resistivity measurements on single crystals of BaThTe4 and BaUTe6 show semiconducting behavior. DFT calculations indicate finite band gaps for BaThTe4 and for BaUTe6, whereas BaUTe4 has a vanishing density of states at the Fermi level.

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 C2h(5)–P2(1)/c of the monoclinic system, whereas BaU2Te5 adopts the (NH4)Pb2Br5 structure type in space group D4h(18)–I4/mcm of the tetragonal system. There are no Q–Q bonds in these structures, so the formulas charge balance as M(2+)(An(4+))2(Q(2–))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 behavior with resistivities of 0.24, 10, and 3.3 mΩ·cm, respectively, at 298 K. Spin-polarized density functional theory in the generalized gradient approximation applied to the four U compounds suggests that they are ferromagnetic. In each compound, the density of states of one spin channel is found to be finite at the Fermi level, whereas there is a gap in the density of states of the other spin channel; this is characteristic of a half-metal.

The new uranium(IV) chlorophosphate compounds UCl4(POCl3) and [U2Cl9][PCl4] have been synthesized by the solid-state reactions of U, P2O5, and PCl5 at 648 K; the compounds UCl3(PO2Cl2) and U2Cl8(POCl3) have been synthesized at 648 K with the same reactants plus added S. Their structures are, respectively, chainlike, a simple salt, three-dimensional, and sheetlike. From ab initio calculations, U2Cl8(POCl3) and UCl3(PO2Cl2) are found to be ferromagnetic, whereas UCl4(POCl3) is found to be antiferromagnetic. U2Cl8(POCl3) is a strong metal, whereas UCl3(PO2Cl2) is a weaker metal. In contrast, UCl4(POCl3) has a finite band gap, with a value of 0.35 eV.

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.

Crystals of tricaesium scandium(III) hexa-chloride were obtained as a side product from the reaction of U, SnCl2, Sc, and S in a CsCl flux at 1073 K. Cs3ScCl6 crystallizes in the Rb3YCl6 structure type. The asymmetric unit comprises three Cs sites, two Sc sites, and six Cl sites, all of which have site symmetry 1, except for the two Sc sites that have site symmetries of 2 and -1, respectively. The structure is composed of isolated [ScCl6](3-) octa-hedra that are surrounded by Cs(+) cations. Two Cs(+) cations have inter-actions with eight Cl(-) anions, while the third has inter-actions with ten Cl(-) anions.

The compounds Ba3FeUS6 and Ba3AgUS6 have been synthesized by the reactions of BaS, U, S, and M (= Fe or Ag) at 1223 K. These two isostructural compounds crystallize in the K4CdCl6 structure type in the trigonal system in space group D3d(6)–R3c. Both structures feature infinite ∞(1)[MUS6(6–)] chains along c that are separated by Ba atoms. The ∞(1)[FeUS6(6–)] chains are formed by the face-sharing of US6 trigonal prisms with FeS6 octahedra; in contrast, the ∞(1)[AgUS6(6–)] chains are formed by the face-sharing of US6 octahedra with AgS6 trigonal prisms. The Ba3FeUS6 compound charge balances with 3 Ba(2+), 1 Fe(2+), 1 U4+, and 6 S(2–), whereas Ba3AgUS6 charge balances with 3 Ba(2+), 1 Ag(1+), 1 U(5+), and 6 S(2–). This structure offers a remarkable flexibility in terms of the oxidation state of the incorporated uranium depending on the oxidation state of the d-block metal. DFT calculations performed with the HSE functional have led to band gaps of 2.3 and 2.2 eV for Ba3FeUS6 and Ba3AgUS6, respectively. From resistivity measurements, the Arrhenius activation energies are 0.12(1) and 0.43(1) eV for Ba3FeUS6 and Ba3AgUS6, respectively.

Crystals of NiUS3 were obtained from the reaction of the elements Ni, U, S, and of GeI2 in a CsCl flux at 1173 K. Nickel(II) uranium(IV) tris-ulfide, NiUS3, has ortho-rhom-bic (Pnma) symmetry and crystallizes in the GdFeO3 structure type. The compound has a perovskite ABQ 3-like structure, with U occupying the inter-stitial sites of a NiS6 framework. The U atoms are coordinated by eight S atoms in a distorted bicapped trigonal-prismatic arrangement. The Ni atoms are coordinated by six S atoms in a slightly distorted octa-hedral arrangement. The asymmetric unit comprises one U site (site symmetry .m.), one Ni site (-1), and two S sites (1 and .m.).

Two new compounds, Ba7UV2S12.5O0.5 and Ba7UFe2S12.5O0.5, have been synthesized in fused-silica tubes by the direct combinations of V or Fe with U, BaS, and S at 1223 K. The compound Ba7UV2S12.5O0.5 crystallizes at 100 K in the Cs7Cd3Br17 structure type in space group D4h(18)–I4/mcm of the tetragonal system. The compound Ba7UFe2S12.5O0.5 crystallizes at 100 K in space group D4h(5)–P4/mbm of the tetragonal system. The structures are very similar with V/S or Fe/S networks in which Ba atoms reside as well as channels large enough to accommodate additional Ba atoms and infinite linear US5O chains. Each U atom is octahedrally coordinated to four equatorial S atoms, one axial S atom, and one axial O atom. The Fe/S network contains a S–S single bond, whereas the V/S network does not. The result is that the Fe3+ compound charge balances with 7 Ba2+, U4+, 2 Fe3+, 10.5 S2–, S2(2–), and 0.5 O2–, whereas the V4+ compound charge balances with 7 Ba2+, U4+, 2 V4+, 12.5 S2–, and 0.5 O2–. Other differences between these two compounds have been characterized by Raman spectroscopy and resistivity measurements. DFT calculations have provided insight into the nature of their bonding. The overall structural motif of Ba7UV2S12.5O0.5 and Ba7UFe2S12.5O0.5 offers a remarkable flexibility in terms of the oxidation state of the incorporated transition metal.

The new uranyl sulfide anion [(UO2)S4](6-) has been synthesized and characterized as a cation-stabilized anion in the compound Na2Ba2(UO2)S4. This compound was synthesized at 873 K from the solid-state reaction of uranium, Na2O2, BaS, and sulfur. The coordination about the U(6+) center in [(UO2)S4](6-) is square bipyramidal with the uranyl O atoms 180° apart and four equatorial S atoms. The Na(+) and Ba(2+) cations form interactions with the uranyl O atoms. Despite the inherent difficulties involved in the synthesis of complex uranium oxysulfides, it is demonstrated that under the right reaction conditions the UO2(2+) species can be produced in situ and result in totally new chalcogen derivatives.

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.

Barium dierbium(III) tetra-sulfide, BaEr2S4, crystallizes with four formula units in the ortho-rhom-bic space group Pnma in the CaFe2O4 structure type. The asymmetric unit contains two Er, one Ba, and four S atoms, each with .m. site symmetry. The structure consists of channels formed by corner- and edge-sharing ErS6 octa-hedra in which Ba atoms reside. The resultant coordination of Ba is that of a bicapped trigonal prism.

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.

Single crystals of CsU(2)Te(6) were synthesized from the reaction of U, Te, and Cs(2)Te(3) at 1273 K. CsU(2)Te(6) crystallizes in the space group Cmcm in the CsTh(2)Te(6) structure type. The asymmetric unit comprises one U (site symmetry m2m), one Cs (m2m; half-occupancy) and two Te atoms (m.. and m2m). The structure of CsU(2)Te(6) consists of infinite [U(2)Te(6)] layers perpendicular to [010] separated by Cs atoms. There are infinite Te-Te-Te linear chains along [001].

The A(2)M(4)U(6)Q(17) compounds Rb(2)Pd(4)U(6)S(17), Rb(2)Pd(4)U(6)Se(17), Rb(2)Pt(4)U(6)Se(17), Cs(2)Pd(4)U(6)S(17), Cs(2)Pd(4)U(6)Se(17), and Cs(2)Pt(4)U(6)Se(17) were synthesized by the high-temperature solid-state reactions of U, M, and Q in a flux of ACl or Rb(2)S(3). These isostructural compounds crystallize in a new structure type, with two formula units in the tetragonal space group P4/mnc. This structure consists of a network of square-planar MQ(4), monocapped trigonal-prismatic UQ(7), and square-antiprismatic UQ(8) polyhedra with A atoms in the voids. Rb(2)Pd(4)U(6)S(17) is a typical semiconductor, as deduced from electrical resistivity measurements. Magnetic susceptibility and specific heat measurements on single crystals of Rb(2)Pd(4)U(6)S(17) show a phase transition at 13 K, the result either of antiferromagnetic ordering or of a structural phase transition. Periodic spin-polarized band structure calculations were performed on Rb(2)Pd(4)U(6)S(17) with the use of the first principles DFT program VASP. Magnetic calculations included spin-orbit coupling. With U f-f correlations taken into account within the GGA+U formalism in calculating partial densities of states, the compound is predicted to be a narrow-band semiconductor with the smallest indirect and direct band gaps being 0.79 and 0.91 eV, respectively.

The compounds ThOS, ThOSe, and ThOTe have been synthesized, and their structures have been determined by means of single-crystal X-ray diffraction methods. All three compounds adopt the PbFCl structure type in the tetragonal space group D(4h)(7) - P4/nmm. More precise crystallographic data have been obtained for ThOS and ThOSe, which had previously only been known from X-ray powder diffraction data. ThOS, ThOSe, and ThOTe are yellow-, orange-, and black-colored, respectively. From single-crystal optical absorption measurements the band gaps are 2.22, 1.65, and 1.45 eV, respectively. Optical band gaps, ionic charges, and densities of states were calculated for the three compounds with the use of Density Functional methods.

Thallium(I) copper(I) thorium(IV) tris-elenide, TlCuThSe₃, crystallizes with four formula units in the space group Cmcm in the KCuZrS₃ structure type. There is one crystallographic-ally independent Th, Tl, and Cu atom at a site of symmetry 2/m.., m2m, and m2m, respectively. There are two crystallographically independent Se atoms at sites of symmetry m.. and m2m. The structure consists of sheets of edge-sharing ThSe₆ octa-hedra and CuSe₄ tetra-hedra stacked parallel to the (010) face, separated by layers filled with chains of Tl running parallel to [100]. Each Tl is coordinated by a trigonal prism of Se atoms.

Black single crystals of A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) have been synthesized by the reactive flux method. These isostructural compounds crystallize in the cubic space group Ia ̅3d at room temperature. The structure comprises a three-dimensional framework built from US(6) octahedra and CuS(3) trigonal planar units with A cations residing in the cavities. There are no S-S bonds in the structure. To elucidate the oxidation state of U in these compounds, various physical property measurements and characterization methods were carried out. Temperature-dependent electrical resistivity measurement on a single crystal of K(6)Cu(12)U(2)S(15) showed it to be a semiconductor. These three A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) compounds all exhibit small effective magnetic moments, < 0.58 μ(B)/U and band gaps of about 0.55(2) eV in their optical absorption spectra. From X-ray absorption near edge spectroscopy (XANES), the absorption edge of A(6)Cu(12)U(2)S(15) is very close to that of UO(3). Electronic band structure calculations at the density functional theory (DFT) level indicate a strong degree of covalency between U and S atoms, but theory was not conclusive about the formal oxidation state of U. All experimental data suggest that the A(6)Cu(12)U(2)S(15) family is best described as an intermediate U(5+)/U(6+) sulfide system of (A(+))(6)(Cu(+))(12)(U(5+))(2)(S(2-))(13)(S(-))(2) and (A(+))(6)(Cu(+))(12)(U(6+))(2)(S(2-))(15).

Nine compounds from the series A(2)M(3)UQ(6) (A = K or Rb or Cs; M = Pd or Pt; Q = S or Se) were synthesized by reacting U, M, and Q in ACl or A(2)Q(x) fluxes. These compounds crystallize with eight formula units in the NaBa(2)Cu(3)O(6) structure type, in space group Fmmm of the orthorhombic system. The structure contains hexagons formed from six edge-sharing square-planar coordinated M atoms, which in turn edge-share with trigonal-prismatically coordinated U atoms, forming layers along (010). These layers are separated by A atoms. Electrical resistivity measurements along the [100] direction of Rb(2)Pd(3)US(6) show typical semiconductor behavior. Magnetic susceptibility measurements on Rb(2)Pd(3)US(6) display marked magnetic anisotropy and unusually low magnetic moments owing to crystalline electric field effects.

The compound Ba(8)Hg(3)U(3)S(18) was obtained from the solid-state reaction at 1123 K of U, HgS, BaS, and S, with BaBr(2)/KBr or BaCl(2) as a flux. This material crystallizes in a new structure type in space group P6 of the hexagonal system with three formula units in a cell of dimensions a = 27.08(1) Å, c = 4.208(2) Å, and V = 2673(2) Å(3). The structure contains infinite chains of US(6) octahedra and nearly linear [S-Hg-S](2-) dithiomercurate anions, separated by Ba(2+) cations. In the temperature range 100-300 K, the paramagnetic behavior of Ba(8)Hg(3)U(3)S(18) can be fit to the Curie-Weiss law, resulting in μ(eff) = 5.40(4) μ(B), or 3.12(2) μ(B)/U. The compound displays an antiferromagnetic transition at T(N) = 59 K. Although the formal oxidation states of Ba, Hg, and S can be assigned as +2, +2, and -2, the oxidation state of U is less certain. On the basis of interatomic distance arguments and the magnetic susceptibility data, the compound is proposed to contain U in both +4 and +5 formal oxidation states.

Zirconium(IV) dilanthanum(III) penta-sulfide, ZrLa(2)S(5), crystallizes with four formula units in the space group Pnma in the U(3)S(5) structure type. The asymmetric unit comprises one Zr, one La and four S atoms. The Zr and three S atoms are situated on mirror planes. The structure consists of LaS(8) face-sharing bicapped distorted trigonal prisms and ZrS(7) edge-sharing monocapped octa-hedra.

β-UPSe was synthesized from the reaction of U(2)Se(3), P and Se in a CsCl flux in a fused-silica tube. It crystallizes with four formula units in the tetra-gonal space group I4/mmm in the UGeTe structure type. The asymmetric unit comprises one U (site symmetry 4mm), one Se (4mm), and one P (mmm.) atom. The U atom is coordinated in a monocapped square-anti-prismatic arrangement, where the square face is formed by P atoms and the other five vertices are Se atoms. The P site is disordered about a mirror plane, showing half-ocupancy for each of the two resulting P atoms. The title structure is related to that of α-UPSe, which crystallizes with two formula units in the tetra-gonal space group P4/nmm in the PbFCl structure type.