Crystallographic disorder and electron scattering on structural two-level systems in ZrAs1.4Se0.5

Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical vapour transport. While their thermodynamic and transport properties are typical for ordinary metals, the electrical resistivity exhibits a shallow minimum at low temperatures. Application of strong magnetic fields does not influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5 apparently originates from interaction between the conduction electrons and structural two-level systems. Significant disorder in the As-Se substructure is inferred from X-ray diffraction and electron microprobe studies

Diethyl 2-[(1-methyl-1H-pyrrol-2-yl)methyl­ene­amino]-5-(2-thienylmethyl­ene­amino)thio­phene-3,4-dicarboxyl­ate

Both imine bonds of the title compound, C21H21N3O4S2, were found to be in the E configuration. The terminal pyrrole and thio­phene rings are twisted by 2.5 (3) and 2.3 (2)°, respectively, from the mean plane of the central thio­phene to which they are attached. The structure is disordered by exchange of the terminal heterocyclic rings; the site occupancy factors are ca 0.8 and 0.2. The crystal packing involves some π–π stacking [3.449 (4) Å between pyrrole and terminal thio­phene rings]

Diethyl 2-amino-5-[(E)-(furan-2-yl­methyl­idene)amino]­thio­phene-3,4-di­carboxyl­ate

In the crystal structure of the title compound, C15H16N2O5S, the azomethine adopts the E configuration. The two heterocyclic rings adopt an anti­periplanar orientation. The mean planes of the thio­phene and furan rings are twisted by 2.51 (4)°. The crystal structure exhibits inter­molecular N—H⋯O hydrogen bonding. π–π stacking is also observed, the centroid-to-centroid distance being 3.770 (4) Å

Th substituted SmFeAsO: structural details and superconductivity with Tc above 50 K

Superconducting poly- and single-crystalline samples of Sm1-xThxFeAsO with partial substitution of Sm3+ by Th4+ were synthesized and grown under high pressure and their structural, magnetic and transport properties are studied. The superconducting Tc reaches values higher than 50 K. Bulk superconducting samples (x = 0.08, 0.15, 0.3) do not show any signs of a phase transition from tetragonal to orthorhombic crystal structure at low temperatures. With Th substitution the unit cell parameters a and c shrink and the fractional atomic coordinate of the As site zAs remains almost unchanged, while that of Sm/Th zSm/Th increases. Upon warming from 5 K to 295 K the expansion of the FeAs layer thickness is dominant, while the changes in the other structural building blocks are smaller by a factor of 1/5, and they compensate each other, since the As-Sm/Th distance appears to contract by about the same amount as the O-Sm/Th expands. The poly- and single-crystalline samples are characterized by a full diamagnetic response in low magnetic field, by a high intergrain critical-current density for polycrystalline samples, and by a critical current density of the order of 8 x 105 A/cm2 for single crystals at 2 K in fields up to 7 T. The magnetic penetration depth anisotropy {\gamma}{\lambda} increases with decreasing temperature, a similar behavior to that of SmFeAsO1-xFy single crystals. The upper critical field estimated from resistance measurements is anisotropic with slopes of 5.4 T/K (H//ab plane) and 2.7 T/K (H//c axis), at temperatures sufficiently far below Tc. The upper critical field anisotropy {\gamma}H is in the range of 2, consistent with the tendency of a decreasing {\gamma}H with decreasing temperature, already reported for SmFeAsO1-xFy single crystals.Comment: 30 pages, 2 tables, 15 figure

Tris(ethane-1,2-diamine-κ2 N,N′)cobalt(II) cis-aqua-2κO-μ-cyanido-1:2κ2 C:N-hepta­cyanido-1κ7 C-bis­(ethane-1,2-diamine-2κ2 N,N′)cobalt(II)molybdenum(IV) dihydrate

The title compound, [Co(C2H8N2)3][CoMo(CN)8(C2H8N2)2(H2O)]·2H2O, is isostructural with the NiII analogue. The MoIV atom is coordinated by eight cyanide ligands, one of which forms a bridge to a CoII atom that is itself coordinated by two bidentate ethane-1,2-diamine (en) ligands and one water mol­ecule. Another CoII complex, coordinated to three bidentate en ligands, acts as the counter-ion. The crystal structure contains O—H⋯N/O, N—H⋯N/O and C—H⋯N/O hydrogen bonds, which form a three-dimensional network

catena-Poly[[penta-μ-benzoato-μ-chlorido-dioxanedineodymium(III)] dioxane 2.5-solvate]

The asymmetric unit of the title compound, [Nd2(C6H5COO)5Cl(C4H8O2)]·2.5C4H8O2, consists of two NdIII ions bridged by one Cl− ion, five benzoate ions and one coordinating 1,4-dioxane mol­ecule. One NdIII ion is nine-coordinate, with a very distorted monocapped square-anti­prismatic geometry. It is coordinated by two chelating carboxyl­ate groups, three monodentate carboxyl­ate groups, one chloride ion and one dioxane mol­ecule. A second independent NdIII ion is eight-coordinated in a distorted square-anti­prismatic geometry by one chelating carboxyl­ate group, five monodentate carboxyl­ate groups and one chloride ion. The chains of the extended structure are parallel to the crystallographic b axis. There is a small amount of void space which is filled with five disordered dioxane solvent mol­ecules per unit cell. The intensity contribution of the disordered solvent molecules was removed by applying the SQUEEZE procedure in PLATON [Spek (2009). Acta Cryst. D65, 148–155]

Diethyl 2,5-bis­[(1E)-(1H-pyrrol-2-yl­methyl­idene)amino]­thio­phene-3,4-dicarboxyl­ate

In the crystal structure of the title compound, C20H20N4O4S, the azomethine group adopt E conformations. The pyrrole units are twisted by 10.31 (4) and 18.90 (5)° with respect to the central thio­phene ring. The three-dimensional network is close packed and involves N—H⋯O, N—H⋯N, C—H⋯N and C—H⋯O hydrogen bonding

Non-Fermi liquid behavior in a fluctuating valence system, the filled skutterudite compound CeRu_{4}As_{12}

Electrical resistivity $\rho$, specific heat C, and magnetic susceptibility $\chi$ measurements made on the filled skutterudite CeRu_4As_{12} reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., $\rho$(T) $\sim$ T^{1.4} and weak power law or logarithmic divergences in C(T)/T and $\chi$(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3^+.Comment: 18 pages, 5 figure

6,6′-(Pyridine-2,6-di­yl)bis­(pyrrolo­[3,4-b]pyridine-5,7-dione)

The title compound, C19H9N5O4, has crystallographically imposed twofold rotational symmetry. The asymmetric unit contains one half-mol­ecule. The crystal structure is stabilized by π–π stacking of inversion-related pyrrolo­[3,4-b]pyridine rings, with a centroid–centroid distance between stacked pyridines of 3.6960 (8) Å. The dihedral angle between the central pyridine ring and the pyrrolo-pyridine side rings is 77.86 (2)° while the angle between the two side chains is 60.87 (2)°

Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2

Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction, magnetic susceptibility, magnetization, electrical resistivity, and specific heat measurements carried out in wide temperature and magnetic field ranges. Moreover, the electronic structure of the compound was studied at room temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The physical properties were analyzed in terms of crystalline electric field and compared with results of ab-initio band structure calculations performed within the density functional theory approach. The compound was found to crystallize in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma -- No.74, Pearson symbol: oI24) with the lattice parameters: a = 7.1330(14) A, b = 9.7340(19) A, and c = 5.6040(11) A. Analysis of the magnetic and XPS data revealed the presence of well localized magnetic moments of trivalent cerium ions. All physical properties were found to be highly anisotropic over the whole temperature range studied, and influenced by exceptionally strong crystalline electric field with the overall splitting of the 4f1 ground multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic moments at TN = 4.70(1)K and their subsequent spin rearrangement at Tt = 4.48(1) K manifest themselves as distinct anomalies in the temperature characteristics of all investigated physical properties and exhibit complex evolution in an external magnetic field. A tentative magnetic B-T phase diagram, constructed for B parallel to the b-axis being the easy magnetization direction, shows very complex magnetic behavior of CeRh3Si2, similar to that recently reported for an isostructural compound CeIr3Si2. The electronic band structure calculations corroborated the antiferromagnetic ordering of the cerium magnetic moments and well reproduced the experimental XPS valence band spectrum.Comment: 32 pages, 12 figures, to appear in Physical Review