Zur Kristallstruktur von Rb2C2 und Cs2C2

On the Crystal Structure of Rb₂C₂ and Cs₂C₂ By reaction of rubidium or caesium solved in liquid ammonia with acetylene AC₂H with A = Rb, Cs was obtained, which was subsequently converted into the binary acetylide A₂C₂ in vacuum at temperatures of 520 K (Rb₂C₂) and 470 K (Cs₂C₂) using a surplus of the respective alkali metal. The crystal structures of the very air sensitive compounds were solved and refined by a combination of both neutron and X‐ray powder diffraction data. Rb₂C₂ as well as Cs₂C₂ coexist in two modifications. The hexagonal modification (P 6 2m, Z = 3) crystallises in the known Na₂O₂ structure type with two crystallographic independent sites for the C₂^2– dumbbells. For the orthorhombic modification (Pnma, Z = 4) a new structure type was found, which is related to the PbCl₂ structure type with ordered C₂^2– dumbbells occupying the Pb sites. Temperature dependent investigations between 4 K and the decomposition temperature by the means of neutron and X‐ray powder diffraction resulted in a very complex dynamic disorder of the C₂ dumbbells, which is still not completely understood. The frequencies of the C–C stretching vibration determined by the help of Raman spectroscopy fit nicely to the results obtained for other alkali metal acetylides and alkali metal hydrogen acetylides. These results seem to indicate that the electronegativity of the alkali metal has a strong influence on the frequency of the C–C stretching vibration.     

The bivalent metal hypophosphites Sr(H2PO2)2, Pb(H2PO2)2 and Ba(H2PO2)2

The structures of isomorphous monoclinic strontium and lead bis­(di­hydrogenphosphate), Sr(H₂PO₂)₂ and Pb(H₂PO₂)₂, and orthorhombic barium bis­(di­hydrogen­phos­phate), Ba(H₂PO₂)₂, consist of layers of hypophosphite anions and metal cations exhibiting square antiprismatic coordination by O atoms. The Sr and Pb atoms are located on sites with point symmetry 2, and the Ba atoms are on sites with point symmetry 222. Within the layers, each anion bridges four metal cations.     

Electrochemical study of (NEt4)2Cl2FeS2MoS2 and (NEt4)2Cl2FeS2MoS2FeCl2

Summary The ability of [MoS₄]^2–, anions to be used as ligands for transition metal ions has been widely demonstrated, especially with Fe²⁺. The present study has been restricted to linear complexes such as (NEt₄)₂ [Cl₂FeS₂MoS₂] and (NEt₄)₂[Cl₂FeS₂MoS₂FeCl₂]. Their electrochemical properties are described: upon electrochemical reduction, these compounds yield MoS₂, as a black precipitate, and an iron complex in solution, assumed to be [SFeCl₂]^2–. The electrochemical reduction goes through two electron transfers, coupled with the breakdown of the molecular skeleton: a DISPl and an ECE mechanism. Depending on the solvent, the following equilibrium may be observed: [Cl₄Fe₂MoS₄]^2–[Cl₂FeMoS₄]^2–+FeCl₂. The equilibrium constant, K_D, was evaluated by differential pulse polarography. K_D is tightly related to the donor number of the solvent.     

Syntheses,Spectroscopic Studies,and Crystal Structures of Me2Sn(O2PPh2)2, Ph2Pb(O2PMe2)2, and Ph2Pb(O2PPh2)2

Me₂Sn(O₂PPh₂)₂ ( 1 ), Ph₂Pb(O₂PMe₂)₂ ( 2 ), and Ph₂Pb(O₂PPh₂)₂ ( 3 ) have been synthesized by the reactions of Me₂SnCl₂ or Ph₃PbCl with the corresponding diorganophosphinic acid in methanol. X‐ray diffraction studies show that the diorganophosphinate groups behave as double bridges between the metal atoms leading to polymeric ring‐chain structures with M₂O₄P₂ (M = Pb, Sn) eight‐membered rings. The organic groups bonded to the metal atoms are in trans‐position in the resulting octahedral arrangement around the metal atoms. The IR and the mass spectra were reported and discussed.     

The alkali hypophosphites KH2PO2, RbH2PO2 and CsH2PO2

The structures of the hypophosphites KH₂PO₂ (potassium hypophosphite), RbH₂PO₂ (rubidium hypophosphite) and CsH₂PO₂ (caesium hypophosphite) have been determined by single‐crystal X‐ray diffraction. The structures consist of layers of alkali cations and hypophosphite anions, with the latter bridging four cations within the same layer. The Rb and Cs hypophosphites are isomorphous.     

Neue AB2X2-Verbindungen mit CaBe2Ge2-Struktur

New AB₂X₂ Compounds with CaBe₂Ge₂ Structure Crystal structure of ternary RELi₂Sb₂ compounds (RE = Ce, Pr, Nd) is reported. The compounds are isotypic and crystallize tetragonally in the CaBe₂Ge₂ structure (space group P4/nmm), which is a modified type of the ThCr₂Si₂ structure.     

BaAg2S2, ein Thioargentat im CaAl2Si2-Strukturtyp

BaAg₂S₂, a Thioargentate with the CaAl₂Si₂-Type Structure BaAg₂S₂ could be obtained as crystalline powder by the reaction of barium-bis[dicyanoargentate(I)] in a stream of hydrogensulfid at 500°C. Single crystals grew at 480°C in an evacuated glass ampoule filled with a flux of potassium thiocyanate and powdery BaAg₂S₂ as solid. BaAg₂S₂ crystallises in the trigonal CaAl₂Si₂-typ structure, a = 4.386(1) Å, c = 7.194(2) Å, space group P3 m1, Z = 1. The structure was determined from four-circle diffractometer data. The silver-sulphur distances are discussed with respect to the corresponding distances of the hitherto known alkaline earth-transition metal pnictides, also crystallizing in the CaAl₂Si₂-typ structure.     

Crystal Structures of [Bu2Sn(O2PPh2)2], [Ph2Sn(O2PPh2)2], and [PhClSn(O2PPh2)OMe]2. Raman Spectra of [Ph2Sn(O2PPh2)2] and [PhClSn(O2PPh2)OMe]2

[(n‐Bu)₂Sn(O₂PPh₂)₂] ( 1 ), and [Ph₂Sn(O₂PPh₂)₂] ( 2 ) have been synthesized by the reactions of R₂SnCl₂ (R=n‐Bu, Ph) with HO₂PPh₂ in Methanol. From the reaction of Ph₂SnCl₂ with diphenylphosphinic acid a third product [PhClSn(O₂PPh₂)OMe]₂ ( 3 ) could be isolated. X‐ray diffraction studies show 1 to crystallize in the monoclinic space group P2₁/c with a = 1303.7(1) pm, b = 2286.9(2) pm, c = 1063.1(1) pm, β = 94.383(6)°, and Z = 4. 2 crystallizes triclinic in the space group , the cell parameters being a = 1293.2(2) pm, b = 1478.5(4) pm, c = 1507.2(3) pm, α = 98.86(3)°, β = 109.63(2)°, γ = 114.88(2)°, and Z = 2. Both compounds form arrays of eight‐membered rings (SnOPO)₂ linked at the tin atoms to form chains of infinite length. The dimer 3 consists of a like ring, in which the tin atoms are bridged by methoxo groups. It crystallizes triclinic in space group with a = 946.4(1) pm, b = 963.7(1) pm, c = 1174.2(1) pm, α = 82.495(6)°, β = 66.451(6)°, γ = 74.922(6)°, and Z = 1 for the dimer. The Raman spectra of 2 and 3 are given and discussed.     

Sc2MgGa2 and Y2MgGa2

Scandium magnesium gallide, Sc₂MgGa₂, and yttrium magnesium gallide, Y₂MgGa₂, were synthesized from the corresponding elements by heating under an argon atmosphere in an induction furnace. These intermetallic compounds crystallize in the tetragonal Mo₂FeB₂‐type structure. All three crystallographically unique atoms occupy special positions and the site symmetries of (Sc/Y, Ga) and Mg are m2m and 4/m, respectively. The coordinations around Sc/Y, Mg and Ga are pentagonal (Sc/Y), tetragonal (Mg) and triangular (Ga) prisms, with four (Mg) or three (Ga) additional capping atoms leading to the coordination numbers [10], [8+4] and [6+3], respectively. The crystal structure of Sc₂MgGa₂ was determined from single‐crystal diffraction intensities and the isostructural Y₂MgGa₂ was identified from powder diffraction data.     

Zur Kenntnis der Dialkalimetalldichalkogenide β-Na2S2, K2S2, α-Rb2S2, β-Rb2S2, K2Se2, Rb2Se2, α-K2Te2, β-K2Te2 und Rb2Te2

On Dialkali Metal Dichalcogenides β-Na₂S₂, K₂S₂, α-Rb₂S₂, β-Rb₂S₂, K₂Se₂, Rb₂Se₂, α-K₂Te₂, β-K₂Te₂ and Rb₂Te₂ The first presentation of pure samples of α- and β-Rb₂S₂, α- and β-K₂Te₂, and Rb₂Te₂ is described. Using single crystals of K₂S₂ and K₂Se₂, received by ammonothermal synthesis, the structure of the Na₂O₂ type and by using single crystals of β-Na₂S₂ and β-K₂Te₂ the Li₂O₂ type structure will be refined. By combined investigations with temperature-dependent Guinier-, neutron diffraction-, thermal analysis, and Raman-spectroscopy the nature of the monotropic phase transition from the Na₂O₂ type to the Li₂O₂ type will be explained by means of the examples α-/β-Na₂S₂ and α-/β-K₂Te₂. A further case of dimorphic condition as well as the monotropic phase transition of α- and β-Rb₂S₂ is presented. The existing areas of the structure fields of the dialkali metal dichalcogenides are limited by the model of the polar covalence.     

Synthesis,Spectral Studies,and Crystal Structure of [Me2ClSnO2AsMe2] and [Et2ClSnO2AsMe2]

The treatment of Me₂SnCl₂ and Et₂SnCl₂ with HO₂AsMe₂ in methanol leads to [Me₂ClSnO₂AsMe₂] ( 1 ) and [Et₂ClSnO₂AsMe₂] ( 2 ), respectively. X‐ray diffraction studies show that the O₂AsMe₂ groups function as bidentate bridge ligands between R₂ClSn units forming polymeric chain structures. 1 consists of double chains, in which the oxygen atoms of each O₂AsMe₂ group of one chain interact in a chelate mode with the tin atom of the other affording seven‐coordinated tin atoms, whereas the structure of 2 is built of single chains in which the tin atoms exhibt a distorted trigonal‐bipyramidal geometry with an axial O‐Sn‐Cl angle of 160°. The vibrational and mass spectra are given and discussed.     

Metall-Schwefelstickstoff-Verbindungen. 13. Die Reaktion von [Ni(HN2S2)2] mit Basen Salze mit den Anionen [Ni(HN2S2)(N2S2)]− und [Ni(N2S2)2]2−

Metal Sulfur Nitrogen Compounds. 13. Reaction of [Ni(HN₂S₂)₂] with Bases. Salts with the Anions [Ni(HN₂S₂)(N₂S₂)]^? and [Ni(N₂S₂)₂]^2? Whereas the complex [Ni(HN₂S₂)₂] reacts with alcoholic solutions of alkaline hydroxides by double deprotonation to the anion [Ni(N₂S₂)₂]^2?, only one proton is removed by the reaction with strong organic bases like tetraalkylammonium, tetraphenylphosphonium, and tetrphenylarsonium hydroxides. The corresponding salts with the anion [Ni(HN₂S₂)(N₂S₂)]^? are formed. The salts containing the tetramethylammonium, tetraethylammonium, tetra-n-butylammonium and tetraphenylarsonium cations were isolated as rather stable, crystalline solids. The structure of the tetraphenylarsonium salt [Ph₄As][Ni(HN₂S₂)(N₂S₂)] was determined by X-ray structure analysis.     

Synthesis and crystal structure of [Nb2(S1.72Se2.28)(S2CNEt2)4]—A solid solution based on [Nb2(μ2, η2-X2)2(S2CNEt2)4], where X2=S2, SSe,and Se2. New model of structure refinement of [Nb2(S2)2(S2CNEt2)4], where X2=S2, SSe,and Se2. New model of structure refinement of [Nb2(S2)2(S2CNEt2)4]

The crystal structure of [Nb₂(S_1.72Se_2.28)(S₂CNEt₂)₄], which is a solid solution based on [Nb₂(μ₂, η²-X₂)₂(S₂CNEt₂)₄], where X₂=S₂, SSe, and Se₂, is determined. The compound was obtained by the reaction of NaS₂CNEt₂ in CH₃CN with the product of the reaction of the NbSe₂Cl₂-KNCS fusion cake with an aqueous solution of Bu₄NBr (yield 30%). The crystals are monoclinic, a=21.319(11), b=7.008(1), c=16.673(8) Å, β=133.99(2)°, V_cell=1792(1) ų, space group C2/m, Z=2, d_calc=1.879 g/cm³ for C₂₀H₄₀N₄Nb₂S_9.72Se_2.28, Syntex P2₁, λCukα, N_meas/corr=2423/1191, R(F)=0.0569 and wR(F²)=0.1282 for 889 F_hkl>4σ(F). The compound is isostructural to the thio analog Nb₂S₄(S₂CNEt₂)₄ studied earlier; in both cases, the molecule is disordered in crystals over two positions. The composition was refined by diffraction data. The results are in good agreement with the Raman and FMB (fast molecule bombardment) mass spectrometry data. The structure of Nb₂S₄(S₂CNEt₂)₄ was refined for the second time using a new model of disorder; as a result of the refinement, a normal value of S?S bond length in the S₂ ligand [2.027(5) Å] was obtained.     

Darstellung und Kristallstruktur der Pnictidoxide Na2Ti2As2O und Na2Ti2Sb2O

Preparation and Crystal Structure of the Pnictide Oxides Na₂Ti₂As₂O and Na₂Ti₂Sb₂O Na₂Ti₂As₂O and Na₂Ti₂Sb₂O were synthesized in form of very easily hydrolysed metallic-grey powders by reaction of Na₂O and TiAs resp. TiSb in sealed tantalum tubes under argon. The tetrahedral bodycentered crystallizing compounds from a modified anti-K₂NiF₄ structure type [1] (also called Eu₄As₂O-type [2,3]), space group I4/mmm (no. 139), with the lattice constants for Na₂Ti₂As₂O: a = 407.0(2) pm, c = 1528.8(4) pm and for Na₂Ti₂Sb₂O: a = 414.4(0) pm, c = 1656.1(1) pm. Magnetic measurements of powder samples of Na₂Ti₂Sb₂O show antiferromagnetic interaction within the Ti—O-layers. Superconductivity was not found by ac-shielding method down to 4 K.     

Comparative XPS Study of Al2O3 and CeO2Sulfation in Reactions with SO2, SO2 + O2, SO2 + H2O,and SO2 + O2 + H2O

The interactions of Al₂O₃, CeO₂, Pt/Al₂O₃, and Pt/CeO₂ films with SO₂, SO₂ + H₂O, SO₂ + O₂, and SO₂ + O₂ + H₂O in the temperature range 300–673 K at the partial pressures of SO₂, O₂, and H₂O equal to 1.5 × 10², 1.5 × 10², and 3 × 10² Pa, respectively, were studied using X-ray photoelectron spectroscopy. The formation of surface sulfite at T 473 K (the S 2p _3/2 binding energy (E _b) is 167.5 eV) and surface sulfate at T 573 K (E _b = 169.2 eV) was observed in the reactions of Al₂O₃ and CeO₂ with SO₂. The formation of sulfates on the surface of CeO₂ occurred much more effectively than in the case of Al₂O₃, and it was accompanied by the reduction of Ce(IV) to Ce(III). The formation of aluminum and cerium sulfates and sulfites on model Pt/Al₂O₃ and Pt/CeO₂ catalysts occurred simultaneously with the formation of surface platinum sulfides (E _b of S 2p _3/2 is 162.2 eV). The effects of oxygen and water vapor on the nature and yield of sulfur-containing products were studied.     

Über LaCo2P2 und andere Neue Verbindungen mit ThCr2Si2- und CaBe2Ge2-Struktur

On LaCo₂P₂ and Other New Compounds with ThCr₂Si₂- and CaBe₂Ge₂-Type Structure The compounds MCo₂P₂ (M = La, Ce, Pr, Nd, Sm, Th, U), MFe₂P₂ (M = La, Ce, U), and ThCo₂As₂ were prepared for the first time. Structure determinations from single crystal X-ray data of LaCo₂P₂ (R = 0.011; 325 F-values), CeCo₂P₂ (R = 0.023; 160 F), PrCo₂P₂ (R = 0.044; 441 F), LaFe₂P₂ (R = 0.024; 511 F), and CeFe₂P₂ (R = 0.016; 183 F) with 11 variable parameters each resulted in atomic positions within the range of the ThCr₂Si₂-type. The powder patterns of ThCo₂P₂, and ThCo₂As₂ show superstructure reflections indicating a CaBe₂Ge₂-type structure. The other compounds can be assigned to the ThCr₂Si₂-type. Chemical bonding of these can be rationalized by a simple band structure model where bonding transition metal – transition metal interactions are important.     

Superconductivity in the intermetallic borocarbides YPd2B2C,YPt2B2C and LaPt2B2C

We report a detailed study of the thermodynamic properties of the conventional phonon-mediated superconductors YPd₂B₂C, YPt₂B₂C and LaPt₂B₂C. Our calculations conducted within the framework of the Migdal-Eliashberg formalism show that the experimental values of the critical temperature cannot be properly reproduced using commonly accepted value of Coulomb pseudopotential. Moreover, we proved that the values of universal ratios of conventional superconductivity appearing in the Bardeen-Copper-Schrieffer (BCS) theory are inconsistent with our results obtained from the investigated borocarbides. The observed differences are connected with the strong/medium-coupling and retardation effects existing in the studied systems.     

Die Kristallstruktur von (PPh4)2[Mo2(O2C?Ph)4Br2] · 2 CH2Br2

Crystal Structure of (PPh₄)₂[Mo₂(O₂C? Ph)₄Br₂] · 2 CH₂Br₂ The title compound, prepared by the reaction of Mo₂(O₂C? Ph)₄ with PPh₄Br and PPh₄N₃, respectively, under the assistance of CH₂Br₂, was characterized by an X-ray structure determination. Space group P2₁/n, Z = 2, R = 0.074 (5261 independent observed reflexions). The lattice dimensions are at ?70°C: a = 1562.9, b = 1406.2, c = 1662.1 pm, β = 94.11°. the compound consists of PPh₄^⊕ ions, CH₂Br₂ molecules, and centrosymmetric anions [Mo₂(O₂C? Ph)₄Br₂]^2?. The axis Br? Mo?Mo–Br is nearly linear (bond angle 175.6°) with bond lengths MoMo = 212.3 pm and Mo? Br = 303 pm, corresponding with a weak electrostatic Mo? Br bond. In the FIR spectrum the Mobr stretching vibration is found at 85 cm^?1, which corresponds with the low value of the force constant of 0.24 N · cm^?1.     

Studies on TiO2/SiO2 and Pd/TiO2/SiO2 Catalysts in Photoreduction of CO2 with H2O to Methanol

The development of industry induced a massive increase in the emission of carbon dioxide into the atmosphere. A large amount of CO₂ and its general availability causes that it could be a cheap reactant in a reaction that runs in a way similar to photosynthesis in plants. Pure TiO₂ and metal doped TiO₂ are the most studied semiconductor catalysts for photoreduction of CO₂. The TiO₂/SiO₂ and Pd/TiO₂/SiO₂ catalysts were prepared and studied by temperature-programmed desorption, X-ray diffraction analysis, SEM-EDS, temperature-programmed reduction and then used for the methanol synthesis. The photoactivity of Pd/TiO₂/SiO₂ catalysts in the reduction of CO₂ with H₂O was tested at room temperature using photoreactor equipped with 16 lamps. The wavelength was characteristic of near ultraviolet. Post-reaction products were identified with gas chromatograph equipped with the flame ionization detector. Pd doping made the catalysts photoactive and the photoactivity of catalysts was changing as follows: 1%Pd/5%TiO₂/SiO₂ > 1% Pd/10% TiO₂/SiO₂ > 1% Pd/15% TiO₂/SiO₂. Optimum ultraviolet radiation time in the photoreduction of CO₂ to methanol was 7 h. An addition of Pd does not change the surface of the carrier.     

(PPh4)2[WO2Cl3]2 · 2 CH2Cl2: Synthese,Schwingungsspektrum und Kristallstruktur

(PPh₄)₂[WO₂Cl₃]₂ · 2 CH₂Cl₂. Synthesis, Vibrational Spectrum, and Crystal Structure Depending on the stoichiometry and the solvent, dichloromethane or 1.2-dichloroethane, WO₂Cl₂ reacts with tetraphenylphosphonium chloride affording (PPh₄)₂[WO₂Cl₄] or (PPh₄)₂[WO₂Cl₃]₂, respectively. Both compounds are easily soluble in dichloromethane, from which they can be crystallized under incorporation of two molecules CH₂Cl₂ per formula unit. The crystalline compounds have been characterized by their IR and Raman spectra. According to the X-ray crystal structure analysis, (PPh₄)₂[WO₂Cl₃]₂ · 2 CH₂Cl₂ crystallizes in the triclinic space group P1 with one formula unit per unit cell (986 independent observed reflexions, R = 0.061). Lattice constants: a = 1100.2, b = 1116.9, c = 1238.4 pm, = 69.40, = 80.46 and = 85.62°. The crystals consist of PPh₄^⊕ ions, centrosymmetric [WO₂Cl₃]₂^2? anions and CH₂Cl₂ molecules. In the anions, the tungsten atoms are linked via two oxo bridges with WO distances of 184 and 252 pm. The distorted octahedral coordination around each tungsten atom is completed by three terminal chloro and one terminal oxo ligand (WO bond length 166 pm), the latter being in trans position to the longer WO bridging bond. (PPh₄)₂[WO₂Cl₄] · 2 CH₂Cl₂ also forms triclinic crystals that are isotypic with (PPh₄)₂[WOCl₅] · 2 CH₂Cl₂ and in which the anions must have orientational disorder.