An Ortho‐silicate‐hydroxide: Rb5[SiO4][OH]

Rb₅[SiO₄][OH] crystallizes in the monoclinc space group C2/m with a = 737.3(1) pm, b = 1073.7(2) pm, c = 1207.2(2) pm, β = 106.07(2)° and Z = 4 (single crystal data; R1= 0.0681 all data). Layers of edge‐connected distorted trigonal prismatic [(OH)Rb₆] entities and isolated tetrahedral [SiO₄] units present the main structural features of this unprecedented structure type.     

Effect of Phosphate on the Adsorption of Glyphosate on Soils,Clay Minerals and Oxides

The effect of phosphate (ortho-phosphate) on the adsorption of the widely used glyphosate herbicide was evaluated with three typical Danish agricultural soils as well as pure oxides (goethite, FeOOH and gibbsite, Al(OH) 3 ) and silicates (illite and montmorillonite), which are considered the most important glyphosate and phosphate adsorbents in soils. Batch experiments where made in order to find out how phosphate affects adsorption of glyphosate and how glyphosate affects adsorbed phosphate. Solution glyphosate was quantified by liquid scintillation counting of 14 C-taggered herbicide and the concentration of phosphate by the molybdenum blue method. All experiments showed competition between phosphate and glyphosate for adsorption sites but the various adsorbents exhibited great variation in affinity for glyphosate and phosphate. Thus, gibbsite and, in particular goethite strongly prefer phosphate, whereas the competition on the silicates is more equal. The current studies showed that the competition in soils is almost equal, but still phosphate affects the sorption of glyphosate in soil. The amount of glyphosate and phosphate adsorbed by the various kinds of adsorbents was found to decrease in the order: oxides > silicates > soils. For the soils tested aluminium oxides, and to a lesser extent iron oxides seem the most important components in determining a soil's ability to adsorb phosphate and glyphosate, whereas the clay content and clay type seem of minor or little importance for adsorption of these species.     

Synthese und Kristallstruktur von Ln2SeSiO4 (Ln = Sm,Dy, Ho) und Sm2TeSiO4

Synthesis and Crystal Structure of Ln₂SeSiO₄ (Ln = Sm, Dy, Ho) and Sm₂TeSiO₄ Single crystals of Ln₂SeSiO₄ (Ln = Sm, Dy, Ho) could be prepared by the reaction of lanthanide metal, selenium and iodine in the ratio 1 : 1 : 2.5 and subsequent reaction with quartz glass powder. Black crystals of Sm₂TeSiO₄ have been obtained in chemical transport experiments of SmTe₂ with iodine in evacuated quartz glass ampoules as by‐products. All chalcogenide silicates crystallize orthorhombically with the space group Pbcm (Z = 4) and the lattice constants: Sm₂SeSiO₄: a = 612.6(1) pm, b = 709.0(1) pm, c = 1094.0(2) pm; Dy₂SeSiO₄: a = 603.6(1) pm, b = 696.4(1) pm, c = 1081.2(2) pm; Ho₂SeSiO₄: a = 601.0(1) pm, b = 693.6(1) pm, c = 1078.6(2) pm; Sm₂TeSiO₄: a = 623.82(8) pm, b = 713.06(7) pm, c = 1112.26(11) pm. The crystal structure is built up of alternating Ln(Se/Te) and LnSiO₄ sheets parallel (001).     

Darstellung und Aufbau der Lanthanoidfluorid‐catena‐Trisilicate M3F[Si3O10] (M = Dy,Ho, Er) im Fluorthalenit‐Typ (Y3F[Si3O10])

Synthesis and Constitution of Fluorothalenite‐Type (Y₃F[Si₃O₁₀]) Fluoride catena‐ Trisilicates M₃F[Si₃O₁₀] with the Lanthanides (M = Dy, Ho, Er) By the reaction of the sesquioxides M₂O₃ with the corresponding trifluorides MF₃ (M = Dy, Ho, Er), SiO₂ and CsCl as flux (molar ratio: 1 : 1 : 3 : 6; 700 °C, 7 d) in evacuated silica tubes and gastight sealed metal capsules made of platinum, niobium or tantalum, respectively, single crystals of the fluoride silicates M₃F[Si₃O₁₀] (monoclinic, P2₁/n; Z = 4; M = Dy: a = 734.06(6), b = 1116.55(9), c = 1040.62(8) pm, β = 97.281(7)°; M = Ho: a = 730.91(6), b = 1111.68(9), c = 1037.83(8) pm, β = 97.238(7)°; M = Er: a = 727.89(6), b = 1107.02(9), c = 1035.21(8) pm, β = 97.209(7)°) were obtained. The most important building groups in the crystal structures of the thalenite type are “isolated” [FM₃]⁸⁺ triangles and catena‐trisilicate anions [Si₃O₁₀]^8–, which contain three [SiO₄] tetrahedra linked to a chain fragment via common corners. This has the shape of a horseshoe where both the terminal tetrahedra show different conformations (eclipsed and staggered) relative to the central unit. Therefore a chelatizing coordination on the same M³⁺ cation via oxygen atoms of both terminal [SiO₄] groups is possible. The narrow area of existence of these fluoride silicates within the lanthanide series will be discussed and structural comparisons with other catena‐trisilicates are presented.     

Sm2Si3O3N4 und Ln2Si2,5Al0,5O3,5N3,5 (Ln = Ce,Pr, Nd,Sm, Gd) – neuer synthetischer Zugang zu N‐haltigen Melilith‐Phasen und deren Einkristall‐Röntgenstrukturanalyse

Sm₂Si₃O₃N₄ and Ln₂Si_2.5Al_0.5O_3.5N_3.5 (Ln = Ce, Pr, Nd, Sm, Gd) – A Novel Synthetic Approach for the Preparation of N‐containing Melilites and X‐Ray Single‐Crystal Structure Determination The high‐temperature synthesis of nitridosilicates using an especially developed rf furnace was now transferred to the preparation of single‐crystalline oxonitridosilicates and oxonitridoaluminosilicates (sialons). Sm₂Si₃O₃N₄ was obtained by the reaction of SrCO₃, Si(NH)₂, and the respective lanthanoides, for Ln₂Si_2.5Al_0.5O_3.5N_3.5 (Ln = Ce, Pr, Nd, Sm, Gd) additionally AlN was used. The compounds were obtained as coarsely crystalline products. Their crystal structures were refined on the basis of single‐crystal X‐ray diffraction data. Sm₂Si₃O₃N₄ (a = 768.89(4), c = 499.60(4) pm) and the isotypic sialons Ce₂Si_2.5Al_0.5O_3.5N_3.5 (a = 779.20(3), c = 506.94(4) pm), Pr₂Si_2.5Al_0.5O_3.5N_3.5 (a = 778.26(4), c = 508.56(5) pm), Nd₂Si_2.5Al_0.5O_3.5N_3.5 (a = 776.15(4), c = 506.7(3) pm), Sm₂Si_2.5Al_0.5O_3.5N_3.5 (a = 772.63(13), c = 502.80(9) pm), and Gd₂Si_2.5Al_0.5O_3.5N_3.5 (a = 774.15(5), c = 506.46(4) pm) are new representatives of the N‐containing melilite structure type (space group P 4 2₁m (no. 113), Z = 2). For the structure analysis specific models were applied, which have been developed by Werner et al. on the basis of powder diffraction data.     

Zwei Formen (A- und B-Typ) von Pr2Te[SiO4]

Two Types (A and B) of Pr₂Te[SiO₄] Two forms of praseodymium(III) telluride ortho-silicate (Pr₂Te[SiO₄]) are obtained as light green, transparent single crystals (A type: bricks, B type: needles, both unsensitive to hydrolysis) from a CsCl melt by reacting Pr, TeO₂ and SiO₂ in stoichiometric ratios (950 °C, 10 d) in evacuated silica tubes. A-Pr₂Te[SiO₄] crystallizes orthorhombically (Pbcm; a = 633.70(3), b = 724.42(4), c = 1125.13(8) pm; Z = 4) with alternatingly arranged monolayers {(Pr2)Te}⁺ and {(Pr1)[SiO₄]}^– parallel (001). Pr1 exhibits a coordination number of nine (6 O and 3 Te) while Pr2 has ten next neighbours (6 O and 4 Te), in which all the oxygen atoms are components of discrete ortho-silicate tetrahedra ([SiO₄]^4–), as also is the case in the B-type structure. The telluride anions show coordination numbers of seven (3 Pr1 and 4 Pr2). B-Pr₂Te[SiO₄] crystallizes monoclinically (P2₁/c; a = 989.90(7), b = 648.03(4), c = 870.68(6) pm, β = 94.307(8)°; Z = 4) with along [100] alternatingly sheethed double layers [{(Pr1)Te}₂]²⁺ and [{(Pr2)[SiO₄]}₂]^2–. This results in coordination numbers of eight (4 O and 4 Te) for Pr1, nine plus one (8 O and 1 + 1 Te) for Pr2, and five plus one (4 Pr1 and 1 + 1 Pr2) for Te. The almost 8% higher density of Pr₂Te[SiO₄] in the A-type structure (D_x = 6.45 g/cm³) compared to that of B-type Pr₂Te[SiO₄] (D_x = 5.98 g/cm³) is quite remarkable.     

Silicates and Perovskites: Two Themes with Variations

An intermediate position between oxosilicates and nitridosilicates on one side and silicates and silicon oxo salts on the other is taken up by Ce₁₆Si₁₅O₆N₃₂. This compound is a perovskite derivative in which the octahedrally coordinated cations have been extensively replaced by tetrahedrally coordinated cations to give the formula Ce₁₆(Si^[6]Si^[4]₁₄□)(O₆N₃₂□₁₀) (^[n]=coordination number, □=lattice vacancy). The presence of vacancies in both the cation and the anion sublattices leads to expectations of ionic conductivity.     

Zwitterionic Spirocyclic λ5Si‐Silicates with Two Bidentate Acetohydroximato(2–) or Benzohydroximato(2–) Ligands: Synthesis,Structure, and Dynamic Stereochemistry

The syntheses of the zwitterionic spirocyclic λ⁵Si‐silicates 7–14 are described. The chiral zwitterions contain a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom, the ate and onium center being connected by an alkylene group. The zwitterions each contain two identical bidentate diolato(2–) ligands that formally derive from acetohydroximic acid or benzohydroximic acid. The stereochemistry and dynamic behavior of these compounds were investigated by experimental and theoretical methods. For this purpose, the zwitterionic λ⁵Si‐silicates 7–14 were studied by solution (¹H, ¹³C, ²⁹Si) and solid‐state (¹³C, ¹⁵N, and ²⁹Si CP/MAS) NMR experiments. In addition, compounds 7 , 8 , 10 , 11 , and 13 were structurally characterized by single‐crystal X‐ray diffraction. The dynamic behavior (intramolecular enantiomerization) of 7 and 13 in solution was studied by VT ¹H NMR experiments. These experimental studies were completed by ab initio investigations of the related anionic model species 15 . The chiral compounds 7–14 exist as (λ)‐ and (δ)‐enantiomers in the solid state and in solution. The trigonal‐bipyramidal structure of the respective Si‐coordination polyhedra, with the two carbon‐linked oxygen atoms in the axial sites, is the energetically most favorable one. The (λ)‐ and (δ)‐enantiomers of 7–14 are configurationally stable in solution on the NMR time scale ([D₆]DMSO, room temperature). They undergo an intramolecular (λ)/(δ)‐enantiomerization (twist‐type mechanism), with an activation free enthalpy of δG^{ = 72–73 kJ mol^–1 (experimentally established for 7 and 13 ; calculated energy barrier for the model species 15 : 66.0 kJ mol^–1).     

Cs4K2CuSi2O8: Synthese,Kristallstruktur, UV‐Vis‐IR‐Daten

Cs₄K₂CuSi₂O₈: Synthesis, Crystal Structure, UV‐Vis‐IR Data Cs₄K₂CuSi₂O₈ may be obtained via a redox reaction of KCuO₂ in the presence of Cs₂O and SiO₂ with the container material (Cu) at 450 °C as blue single crystals which are sensitive to moisture. Powder samples were obtained by annealing intimate mixtures of the binary oxides under an inert gas atmosphere (Ar) in sealed Ag containers at 500 °C. The crystal structure contains isolated trimeric anions of [O₂SiO₂CuO₂SiO₂]^6–. Cu²⁺ in square‐planar coordination share trans‐edges with [SiO₄] tetrahedra. Spectroscopic investigations focus on the bonding situation of the [CuO₄] unit (AOM) and characteristic vibrational modes of the silicate.     

快速测定水化硅酸钙结晶度的XRD方法

本文根据水化硅酸钙的特征衍射谱形,提出了一个快速测定其结晶度的方法,并达到了预期的效果。