SrPt3In2- an orthorhombically distorted coloring variant of SrIn5.

The new intermetallic phase SrPt3In2 was synthesized by induction-melting of the elements in a sealed tantalum ampoule followed by long-term annealing for crystal growth. The SrPt3In2 structure was refined from single crystal X-ray diffraction data: Imma, a = 1674.7(6), b = 921.2(4), c = 971.2(4) pm, wR2 = 0.0551, 1192 F2 values and 55 variables. Electronic structure calculations indicate strong covalent Pt-In bonding and a substantial charge transfer from the strontium atoms to the three-dimensional [Pt3In2]δ- polyanionic network. The strontium atoms fill larger cavities within the network and the bonding of strontium to the polyanion is of the electrostatic type. The Bader charge calculations classify SrPt3In2 as a ternary platinide. The close relationship between the SrPt3In2 structure and the aristotype CaCu5 is discussed on the basis of a group-subgroup scheme in the Bärnighausen formalism along with other CaCu5 coloring variants and superstructures.

Red-emitting K3HF2WO2F4:Mn4+ for application in warm-white phosphor-converted LEDs - optical properties and magnetic resonance characterization.

We report novel efficient Mn4+ phosphors of composition K3HF2MO2F4:Mn4+ (M = Mo, W) containing [HF2]- and octahedral [MO2F4]2- building units. The phosphor exhibits strong absorption at 450 nm and an external quantum yield of 90%. K3HF2WO2F4:0.01Mn4+ provides a sufficiently high quenching temperature T1/2 of about 400 K and is applicable as a converter for (In,Ga)N LEDs. The EPR spectrum is consistent with the presence of a MnF62- species at giso = 1.983. 19F MAS NMR results confirm the 2 : 1 ratio of the metal-bound fluoride species to the hydrogen difluoride group as predicted from the chemical formula. There are two distinct M-bonded species in a 1 : 1 ratio, indicating that the W and Mo octahedra are exclusively of the MO2F42- type, with the two oxygen atoms in cis-position. Their extremely sharp 19F resonances indicate a fast, near-isotropic reorientational process at room temperature that is on the millisecond timescale. For the HF2- group, the 19F and 1H MAS NMR spinning sideband profiles reveal the geometry of a linear centrosymmetric three-spin system with an H-F bond distance of 1.14 Å.

Structural phase transitions in YPtGe2 and GdPtGe2.

The germanides YPtGe2 and GdPtGe2 were synthesized from REGe2 precursor compounds and platinum by arc-melting and their structures were studied on the basis of temperature-dependent single crystal X-ray diffraction data. At room temperature both germanides adopt the orthorhombic YIrGe2 type structure, space group Immm, with enhanced U11 displacement parameters for the Ge1 atoms. Below 174 and 145 K, respectively, satellite reflections emerge in the diffraction patterns, giving rise to modulations. The low-temperature structures were refined in the superspace group Pnnn(1/2,1/2,γ)qq0 (48.1.11.3). The structural phase transition is also evident in the magnetic susceptibility, specific heat and resistivity data. The high- and low-temperature modifications are discussed on the basis of a group-subgroup scheme.

A ZrNiAl related high-pressure modification of CeRuSn.

Monoclinic CeRuSn with its own structure type transforms to a high-pressure modification at 11.5 GPa and 1470 K (1000 t press, Walker type module). The structure of the high-pressure phase was refined from X-ray single crystal diffractometer data at room temperature. The HP-CeRuSn subcell structure adopts the ZrNiAl type: P6[combining macron]2m, a = 751.4(3) and c = 394.6(2) pm, wR2 = 0.0787, 310 F(2) values and 15 variables. The Ru2 atoms within the Sn6 trigonal prisms show a strongly enhanced U33 parameter. Weak satellite reflections indicate a commensurate modulation: (3 + 1)D superspace group P31m(1/3,1/3,γ)000, a = 751.4(3) and c = 394.6(2) pm, γ = -1/3, wR2 = 0.0786, 1584 F(2) values, 32 variables for the main reflections and wR2 = 0.3757 for the satellites of 1(st) order. A description of this new superstructure variant of the ZrNiAl type is possible in a transformed 3D supercell with the space group R3m and Z = 9. The driving force for formation of the modulation is strengthening of Ru-Sn bonding within the comparatively large Ru@Sn6 trigonal prisms. Electronic structure calculations point to an almost depleted Ce 4f shell. This is substantiated by temperature-dependent magnetic susceptibility data. Fitting of the data within the interconfiguration fluctuation model (ICF) resulted in cerium valences of 3.41 at 10 K and 3.31 at 350 K. Temperature dependent specific heat data underline the absence of magnetic ordering.

New quaternary arsenide oxides with square planar coordination of gold(I) - structure, (197)Au Mössbauer spectroscopic, XANES and XPS characterization of Nd10Au3As8O10 and Sm10Au3As8O10.

The quaternary gold(I) arsenide oxides Nd10Au3As8O10 and Sm10Au3As8O10 were synthesized in sealed quartz ampoules from the rare earth (RE) elements, their appropriate sesquioxides, arsenic, arsenic(III) oxide and finely dispersed gold at maximum annealing temperatures of 1223 K. Both structures were refined from X-ray single crystal diffractometer data at room temperature and at 90 K. Nd10Au3As8O10 and Sm10Au3As8O10 crystallize with a new structure type that derives from the BaAl4 structure through distortions and formation of ordered vacancies. The structures consist of stacked polycationic [RE10O10](10+) layers with oxygen in tetrahedral rare earth coordination and polyanionic [Au(I)3(As2)4](10-) layers with gold in square planar or rectangular planar coordination of four arsenic dumbbells (255 pm As1-As2). In contrast to the well known ionic rare earth oxide layers, the gold arsenide layers rather show covalent bonding and account for the metallic nature of these two new arsenide oxides. This is confirmed by electronic structure calculations and resistivity measurements. The oxidation state of gold was investigated by (197)Au Mössbauer, X-ray absorption near edge structure (XANES) and photoelectron (XPS) spectroscopy. Due to missing comparative gold arsenide compounds, the monovalent gold phosphide oxides RE2AuP2O were measured for comparison. The XANES measurements additionally comprise monovalent gold arsenides REAuAs2. The XPS study contains BaAuAs as reference compound instead. Combination of all data clearly indicates Au(I), which was not observed in square planar coordination up to now. Temperature dependent magnetic susceptibility data show Curie-Weiss paramagnetism for Nd10Au3As8O10 and no magnetic ordering down to 2.5 K. Sm10Au3As8O10 shows the typical Van Vleck type paramagnetism for samarium compounds along with a transition to an antiferromagnetically ordered state at TN = 8.6 K.

Refined crystal structure and idealized structure of mixed-valent Eu4F5(CN2)2: transition possible.

The new europium fluoride carbodiimide Eu(4)F(5)(CN(2))(2) was synthesized by solid state reaction from mixtures of EuF(3) and Li(2)(CN(2)) at 700 °C. The crystal structure as refined by single crystal X-ray diffraction (P ̅42(1)c, no. 114, a = 16.053(1) Å, c = 6.5150(6) Å, Z = 8) reveals three crystallographically distinct [N═C═N](2-) ions in the structure of mixed-valent Eu(4)F(5)(CN(2))(2). The presence of one Eu(3+) and three Eu(2+) per formula unit Eu(4)F(5)(CN(2))(2) is confirmed by magnetic measurements and (151)Eu-Mössbauer spectroscopy. The arrangement of Eu ions and gravity centers of [NCN](2-) ions in the structure of Eu(4)F(5)(CN(2))(2) follow the motif formed by atoms in the CuAl(2)-type structure. A possible high-symmetry structure of Eu(4)F(5)(CN(2))(2) is discussed on the basis of a group-subgroup scheme.

Indium flux-growth of Eu2AuGe3: a new germanide with an AlB2 superstructure.

The germanide Eu(2)AuGe(3) was obtained as large single crystals in high yield from a reaction of the elements in liquid indium. At room temperature Eu(2)AuGe(3) crystallizes with the Ca(2)AgSi(3) type, space group Fmmm, an ordered variant of the AlB(2) type: a = 857.7(4), b = 1485.5(10), c = 900.2(4) pm. The gold and germanium atoms build up slightly distorted graphite-like layers which consist of Ge(6) and Au(2)Ge(4) hexagons, leading to two different hexagonal-prismatic coordination environments for the europium atoms. Magnetic susceptibility data showed Curie-Weiss law behavior above 50 K and antiferromagnetic ordering at 11 K. The experimentally measured magnetic moment indicates divalent europium. The compound exhibits a distinct magnetic anisotropy based on single crystal measurements and at 5 K it shows a metamagnetic transition at ∼10 kOe. Electrical conductivity measurements show metallic behavior. The structural transition at 130 K observed in the single crystal data was very well supported by the conductivity measurements. (151)Eu Mössbauer spectroscopic data show an isomer shift of -11.24 mm/s at 77 K, supporting the divalent character of europium. In the magnetically ordered regime one observes superposition of two signals with hyperfine fields of 26.0 (89%) and 3.5 (11%) T, respectively, indicating differently ordered domains.

High- and low-temperature modifications of Sc3RuC4 and Sc3OsC4--relativistic effects, structure, and chemical bonding.

Sc(3)RuC(4) and Sc(3)OsC(4) were synthesized by arc-melting and subsequent annealing. At room temperature, they crystallize with the Sc(3)CoC(4) structure, space group Immm. At 223 and 255 K, Sc(3)RuC(4) and Sc(3)OsC(4), respectively, show a monoclinic distortion caused by a pair-wise displacement of the one-dimensional [Ru(C(2))(2)](delta-) and [Os(C(2))(2)](delta-) polyanions, which are embedded in a scandium matrix. Superstructure formation leads to shorter Ru-Ru and Os-Os distances of 316 pm between adjacent [Ru(C(2))(2)](delta-) and [Os(C(2))(2)](delta-) polyanions. Each ruthenium (osmium) atom is covalently bonded to four C(2) pairs with Ru-C (Os-C) distances of 220-222 pm. A comparison of the C-C bond distances at room temperature in Sc(3)TC(4) with T representing a group 8 transition metal (Fe, Ru, Os) reveals a minimum in the case of the 4d metal Ru: 144.98(11) pm (Fe), 142.8(7) pm (Ru), and 144.6(4) pm (Os). Analysis of the local electronic structure of the [T(C(2))(2)] moieties hints at a complex interplay between chemical bonding and relativistic effects, which is responsible for the V-shaped pattern of the C-C bond distances (long, short, and long for T = Fe, Ru, and Os, respectively). Relativistic effects lead to a strengthening of covalent T-C bonding. This is shown on the basis of periodic DFT calculations by a significant increase of the charge density at the T-C bond critical points (0.55 < 0.57 < 0.64 eA(-3)) down the row of group 8 elements. These structural characteristics and topological features do not change in the corresponding low-temperature phases of Sc(3)RuC(4) and Sc(3)OsC(4). However, topological analyses of theoretical charge density distributions reveal distinct changes of the valence shell charge concentrations at the transition metal centers due to the monoclinic distortions. Presumably, the local electronic situation at the transition metals reflects the origin and extent of these monoclinic distortions.

Experimental electron density of the complex carbides Sc3[Fe(C2)(2)] and Sc3[Co(C2)(2)].

The nature of chemical bonding in the complex carbides Sc3[Fe(C2)2] (1) and Sc3[Co(C2)2] (2) has been explored by combined experimental and theoretical charge density studies. The structures of these organometallic carbides contain one-dimensional infinite TC4 (T = Fe, Co) ribbons embedded in a scandium matrix. Bonding in 1 and 2 was studied experimentally by multipolar refinements based on high-resolution X-ray data and compared to scalar-relativistic electronic structure calculations using the augmented spherical wave method. Besides substantial covalent T-C bonding within the TC4 ribbons, one also observes discrete Sc-C bonds of noticeable covalent character. Furthermore, our study highlights that even tiny differences in the electronic band structure of solids might be faithfully recovered in the properties of the Laplacian of the experimental electron density. In our case, the increase of the Fermi level in the organometallic Co(d9) carbide 2 relative to its isotypic Fe(d8) species 1 is reflected in the charge density picture by a significant change in the polarization pattern displayed by valence shell charge concentrations of the transition metal centers in the TC4 units. Hence, precise high-resolution X-ray diffraction data provide a reliable tool to discriminate and analyze the local electronic structures of isotypic solids, even in the presence of a severe coloring problem (Z(Fe)/Z(Co) = 26/27).

New stannide ScAgSn: determination of the superstructure via two-dimensional 45Sc solid state NMR.

The new stannide ScAgSn was synthesized by induction melting of the elements in a sealed tantalum tube and subsequent annealing. ScAgSn crystallizes with a pronounced subcell structure: ZrNiAl type, P2m, a = 708.2(2) pm, c = 433.9(1) pm, wR2 = 0.1264, 321 F2 values, and 14 variables. The Guinier powder pattern reveals weak superstructure reflections pointing to a TiFeSi-type structural arrangement: I2cm, a = 708.1(1) pm, b = 1225.2(2) pm, c = 869.9(1) pm, wR2 = 0.0787, 5556 F2 values, and 49 variables. So far the growth of high-quality single crystals failed. Determination of the superstructure was partly based on merohedral triplet X-ray data augmented by 119Sn Mössbauer spectroscopy and 119Sn and 45Sc solid-state NMR data. In particular, the observation of three crystallographically inequivalent sites in 45Sc NMR triple quantum magic-angle spinning (TQ-MAS) NMR spectra provided unambiguous proof of the superstructure proposed. The ScAgSn structure consists of a three-dimensional [AgSn] network (with Ag-Sn distances between 273 and 280 pm) in which the scandium atoms are located in distorted hexagonal channels, each having five tin and two silver nearest neighbors. Both crystallographically independent tin sites have a tricapped trigonal prismatic coordination, that is, [Sn1Sc6Ag3] and [Sn2Ag6Sc3] environments, which are well distinguished in the 119Sn NMR and Mössbauer spectra because of their different site symmetries.

Structure and lithium dynamics of Li2AuSn2--a ternary stannide with condensed AuSn4/2 tetrahedra.

The new stannide Li(2)AuSn(2) was prepared by reaction of the elements in a sealed tantalum tube in a resistance furnace at 970 K followed by annealing at 720 K for five days. Li(2)AuSn(2) was investigated by X-ray diffraction on powders and single crystals and the structure was refined from single-crystal data: Z=4, I4(1)/amd, a=455.60(7), c=1957.4(4) pm, wR2=0.0681, 278 F(2) values, 10 parameters. The gold atoms display a slightly distorted tetrahedral tin coordination with Au-Sn distances of 273 pm. These tetrahedra are condensed through common corners leading to the formation of two-dimensional AuSn(4/2) layers. The latter are connected in the third dimension through Sn-Sn bonds (296 pm). The lithium atoms fill distorted hexagonal channels formed by the three-dimensional [AuSn(2)] network. Modestly small (7)Li Knight shifts are measured by solid-state NMR spectroscopy that are consistent with a nearly complete state of lithium ionization. The noncubic local symmetry at the tin site is reflected by a nuclear electric quadrupolar splitting in the (119)Sn Mössbauer spectra and a small chemical shift anisotropy evident from (119)Sn solid-state NMR spectroscopy. Variable-temperature static (7)Li solid-state NMR spectra reveal motional narrowing effects at temperatures above 200 K, revealing lithium atomic mobility on the kHz time scale. Detailed lineshape as well as temperature-dependent spin lattice relaxation time measurements indicate an activation energy of lithium motion of 27 kJ mol(-1).