Yuandong Wu

K2Ln2As2Se9 (Ln = Sm, Gd): the first quaternary rare-earth selenoarsenate compounds with a 3D framework containing chairlike As2Se4 units.

The new compounds K(2)Ln(2)As(2)Se(9) (Ln = Sm, Gd) were obtained by applying the reactive flux method. The structure consists of a three-dimensional (3D) [Ln(2)As(2)Se(9)](2-) framework with K(+) ion-filling tunnels running along the b axis. The two unique Ln(3+) cations are coordinated by two Se(2)(2-) dumbbells, two AsSe(3)(3-) pyramids, and one chairlike As(2)Se(4)(2-) unit in a bicapped trigonal-prismatic geometry. The Ln(3+)-centered trigonal prisms share triangular faces with neighboring prisms, forming one-dimensional chains along the b axis. These chains are linked to each other to form layers by sharing Se(2-) anions on the capped sites of the trigonal prisms. The As(2)Se(4) units connect these layers to form the 3D framework.

Structural diversity of rare earth and transition metal thiophosphates

Technological interest in the design of solid state materials has stimulated recent research into the development of mild molten polychalcophosphate salt fluxes for the synthesis of complex, multinary rare earth and transition metal thiophosphate compounds. The reaction pathways from elemental or metal sulfide sources can be influenced by a variety of often interdependent factors of which counter cation sizes and charges, basicity, and temperature are of paramount importance. In rare earth and transition metal containing thiophosphates the dominating structural building units are tetrahedral [PS4]3− or ethane-like [P2S6]4− anions. Hierarchical topological relations between individual members of structural families of the type AmMnPySz (A = alkali metal, M = rare earth or transition metal) can be established that provide a detailed insight into probable mechanisms of formation. The findings enable the development of guidelines for the employment of suitable counter cations in controlling the condensation of small species into chains, layers or frameworks.

Syntheses, structures, and spectroscopic properties of K9Nd[PS4]4, K3Nd[PS4]2, Cs3Nd[PS4]2, and K3Nd3[PS4]4.

Four new quaternary alkali neodymium thiophosphates K 9Nd[PS 4] 4 ( 1), K 3Nd[PS 4] 2 ( 2), Cs 3Nd[PS 4] 2 ( 3), and K 3Nd 3[PS 4] 4 ( 4) were synthesized by reacting Nd with in situ formed fluxes of K 2S 3 or Cs 2S 3, P 2S 5 and S in appropriate molar ratios at 973 K. Their crystal structures are determined by single crystal X-ray diffraction. Crystal data: 1: space group C2/ c, a = 20.1894(16), b = 9.7679(5), c = 17.4930(15) A, beta = 115.66(1) degrees , and Z = 4; 2: space group P2 1/ c, a = 9.1799(7), b = 16.8797(12), c = 9.4828(7) A, beta = 90.20(1) degrees , and Z = 4; 3: space group P2 1/ n, a = 15.3641(13), b = 6.8865(4), c = 15.3902(13) A, beta = 99.19(1) degrees , and Z = 4; 4: space group C2/ c, a = 16.1496(14), b = 11.6357(7), c = 14.6784(11) A, beta = 90.40(1) degrees , and Z = 4. The structure of 1 is composed of one-dimensional (1) infinity{Nd[PS 4] 4} (9-) chains and charge balancing K (+) ions. Within the chains, eight-coordinated Nd (3+) ions, which are mixed with K (+) ions, are connected by [PS 4] (3-) tetrahedra. The crystal structures of 2 and 3 are characterized by anionic chains (1) infinity{Nd[PS 4] 2} (3-) being separated by K (+) or Cs (+) ions. Along each chain the Nd (3+) ions are bridged by [PS 4] (3-) anions. The difference between the structures of 2 and 3 is that in 2 the Nd (3+) ions are coordinated by four edge-sharing [PS 4] (3-) tetrahedra while in 3 each Nd (3+) ion is surrounded by one corner-sharing, one face-sharing, and two edge-sharing [PS 4] (3-) tetrahedra. The structure of 4 is a three-dimensional network with K (+) cations residing in tunnels running along [110] and [110]. The {Nd(1)S 8} polyhedra share common edges with four [PS 4] tetrahedra forming one-dimensional chains (1) infinity{Nd[PS 4] 2} (3-) running along [110] and [110]. The chains are linked by {Nd(2)S 8} polyhedra yielding the final three-dimensional network (3) infinity{Nd[PS 4] 2} (3-). The internal vibrations of both crystallographically independent [PS 4] (3-) anions of 2- 4 have been assigned in the range 200-650 cm (-1) by comparison of their corresponding far/mid infrared and Raman spectra (lambda exc = 488 nm) on account of locally imposed C 1 symmetry. In the Fourier-transform-Raman spectrum (lambda exc = 1064 nm) of 2- 4, very similar well-resolved electronic Raman (ER) transitions from the electronic Nd (3+) ground-state to two levels of the (4)I 9/2 ground manifold and to the six levels of the (4)I 11/2 manifold have been determined. Resonant Raman excitation via a B-term mechanism involving the (4)I 15/2 and (4)F 3/2 intermediate states may account for the significant intensity enhancement of the ER transitions with respect to the symmetric P-S stretching vibration nu 1. Broad absorptions in the UV/vis/NIR diffuse reflectance spectrum at 293 K in the range 5000-25000 cm (-1) of 2- 4 are attributed to spin-allowed excited quartet states [ (4)(I < F < S < G < D)] and spin-forbidden doublet states [ (2)(H < G < K < D < P)] of Nd (3+). A luminescense spectrum of 3 obtained at 15 K by excitation with 454.5 nm shows multiplets of narrow lines that reproduce the Nd (3+) absorptions. Sharp and intense luminescence lines are produced instead by excitation with 514.5 nm. Lines at 18681 ( (4)G 7/2), 16692 ( (4)G 5/2), 14489 ( (4)F 9/2), and 13186 cm (-1) ( (4)F 7/2) coincide with the corresponding absorptions. Hypersensitive (4)G 5/2 is split by 42 cm (-1). The most intense multiplet at about 16500 cm (-1) is assigned to the transition from (4)G 5/2 to the Stark levels of the ground manifold (4)I 9/2.

Synthesis, Crystal Structures and Spectroscopic Properties of RbBaTaS4 and K2BaTa2S11

Single crystals of RbBaTaS4 (1) and K2BaTa2S11 (2) were obtained from the reactions of Ta, with in situ formed fluxes of A2S3 (A = K, Rb), BaS, and S at 500 °C. Compound 1 crystallizes in the orthorhombic space group Pnma with a = 9.3286(5), b = 7.0391(4), c = 12.4365(7) Å, V = 816.6(1) Å3, Z = 4. Compound 2 crystallizes in the monoclinic space group P21/c with a = 14.5280(10), b = 12.6347(7), c = 17.5148(12) Å , β = 94.744(8)°, V = 3203.9(4) Å3, Z = 4. The structure of RbBaTaS4 (1) consists of isolated tetrahedral [TaS4]3− anions and Rb+ and Ba2+ cations. The Ba2+ cations are surrounded by nine sulfur atoms forming distorted tricapped trigonal prisms, whereas the Rb+ cations are in an irregular environment of ten sulfur atoms. The structure of K2BaTa2S11 (2) consists of two different dinuclear [Ta2S11] units which are separated by Ba2+ and K+ cations. The Ta atoms are coordinated by S22− and S2− ligands according to the mode [Ta2(μ2-S)(μ2-η2,η1- S2)2(η2-S2)2(S)2]4−. Each Ta atom is surrounded by seven sulfur ions forming strongly distorted pentagonal bipyramids. The two [TaS7] polyhedra share a common face in the [Ta2S11] unit. The K+ and Ba2+ cations are statistically distributed over the crystallographic sites. Compound 2 has also been characterized by UV/Vis diffuse reflectance, IR and Raman spectroscopy Graphical Abstract Synthesis, Crystal Structures and Spectroscopic Properties of RbBaTaS4 and K2BaTa2S11

Low Dimensional Materials: Syntheses, Structures, and Optical Properties of Rb2CuTaS4, Rb2CuTaSe4, RbCu2TaSe4, K3Ag3Ta2Se8, and Rb3AgTa2Se12

The new compounds Rb2CuTaS4 (1), Rb2CuTaSe4 (2), RbCu2TaSe4 (3), K3Ag3Ta2Se8 (4), and Rb3AgTa2Se12 (5) have been synthesized by the reactive flux method at 773 or 873 K. Their crystal structures were determined by single crystal X-ray diffraction. Crystal data for 1: space group Fddd, a = 5.598(1), b = 13.512(4), c = 23.854(5) Å , Z = 8; Crystal data for 2: space group Fddd, a = 5.782(1), b = 13.924(3), c = 24.653(5) Å , Z = 8; Crystal data for 3: space group C2cm, a = 5.7218(3), b = 19.2463(13), c = 7.7456(5) Å , Z = 4; Crystal data for 4: space group C2/c, a = 25.1374(19), b = 6.1007(3), c = 14.4030(11) Å , β = 119.703(8)◦, Z = 4; Crystal data for 5: space group P21/n, a = 9.8186(6), b = 13.7462(11), c = 15.7368(9) Å , β = 96.681(7)◦, Z = 4. The compounds 1 and 2 are built up of 1∞[CuTaQ4]2− anionic chains which are formed by edge-sharing CuQ4 and TaQ4 tetrahedra. The rubidium cations are located between the chains. Compound 3 consists of 2∞[Cu2TaSe4]− anionic layers separated by rubidium cations. The anionic layers are formed by1∞[CuTaSe4]2− chains which are connected by CuSe4 tetrahedra that share common edges with the TaSe4 tetrahedra of neighboring chains. In compound 4 1∞[Ag3Ta2Se8]3− anionic chains are found which are separated by potassium cations. These chains are formed by successive corner sharing of AgSe4 tetrahedra and edge sharing between AgSe4 and TaSe4 tetrahedra. All three structures are closely related with the sulvanite (Cu3VS4) structure type. Compound 5 contains a one dimensional 1∞[AgTa2Se12]3− anionic chain formed by interconnection of AgSe4 tetrahedra and [Ta2Se11] units. In the structure three monoselenide, three diselenide, and one triselenide anions are found. Raman and far-IR spectroscopic data of compounds 1 and 4 were collected and an interpretation is presented.