Bis[4‐(dimethylamino)pyridine‐κN1]silver(I) nitrate dihydrate

The title compound, [Ag(C₇H₁₀N₂)₂]NO₃·2H₂O or [Ag(dmap)₂]NO₃·2H₂O, where dmap is 4‐(dimethylamino)pyridine, has a distorted linear coordination geometry around the Ag^I ion. A novel pattern of water–nitrate hydrogen‐bonded anionic strands is formed in the c direction, with the cationic [Ag(dmap)₂]⁺ monomers trapped between them. The Ag^I ion and the nitrate group atoms, as well as the water molecules (including the H atoms), are on a crystallographic mirror plane (Wyckoff position 4a). The influence of bulky methyl substituents in position 4 of the 4‐(dimethylamino)pyridine ligand on packing is discussed. The absolute structure was determined unequivocally.     

Synthese von 2-Oxo-2H-pyran-5-Carboxylat-Derivaten

Synthesis of 2-Oxo-2H-pyran-5-carboxylate Derivatives 3-Substituted diethyl pent-2-enedioates are easily formylated by means of ethyl formate/TiCl⁴/4-methylmorpholine to produce the ethoxymethylene derivatives, which are smoothly cyclized either with HCOOH or PPA to corresponding 2-oxo-2H-pyran-5-carboxylate derivatives.     

Aromatic nucleophilic substitution. Part 2. Preparation of novel 3-substituted xanthone and thioxanthone derivatives

The novel 3-nitro-9-oxo-9H-xanthene- and 3-nitro-9-oxo-9H-thioxanthene-l-carboxylic acids 2a–d were prepared by intramolecular acylation of 3-aryloxy- and 3-arylthio-5-nitrophthalic anhydrides 1 (Scheme). The 3-nitro group was readily substituted by O- and S-nucleophiles and halide and azide ions to give a range of 3-substituted thioxanthone derivatives 3 with varied λ_max.     

Improved resolution and powder neutron diffraction research on the KSN-2 diffractometer

The diffractometer KSN-2 placed at the 10 MW reactor VVRS-M in e near Prague provides the possibility for powder structure analysis of silicates. The characteristic parameters of the device are given.     

Über den Einfluss der pK-Werte von Anilinen auf die Bildung und Folgereaktionen von substituierten Butadienen aus Cumalinsäure-methylester

The Influence of Aniline pK Values on the Formation and Reactivity of Substituted Butadienes from Methyl Coumalate The product of the reaction between 2 equiv. of methyl coumalate ( 1 ) and 1 equiv. of a substituted aromatic amine depends on the pK value of the latter. Aromatic amines with pK values between 1.05 and 2.8 produce bicyclic lactones 4 , whereas those with higher pK values also give 2-azabicyclo[3.3.1]nona-3,7-diene-9-carboxylic acids 9 . The latter, products of the intramolecular Diels-Alder reaction 8 → 9 , may in certain cases even prevail.     

A pseudo‐merohedrally twinned rare‐earth sulfate: K6[Ce(HSO4)2(SO4)4]·H2O,a novel structure type

A novel structure type of an acidic rare‐earth sulfate, hexa­potassium cerium dihydrogensulfate tetra­sulfate monohydrate, is reported. The crystal is twinned, mimicking tetra­gonal symmetry. The Ce^IV atom is nine‐coordinate, connecting to one corner‐sharing and four edge‐sharing sulfate groups. One of the potassium ions is disordered over two general positions. The compound is unique as it contains rare‐earth monomers, [Ce(HSO₄)(SO₄)₄]⁵⁻. The structure is composed of these monomers, water mol­ecules, discrete hydrogensulfate ions and potassium ions held together by ionic inter­actions. There are two types of alternating layers in the structure, with compositions [K₄Ce(HSO₄)(SO₄)₄]⁻ and [K₂(HSO₄)(H₂O)]⁺.     

The orthorhombic polymorph of diammonium trichromate(VI) decaoxide, <Emphasis Type="Italic">α</Emphasis>–(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>3</Subscript>O<Subscript>10</Subscript>

Synthesis and crystal structure of a trichromium(VI) decaoxide compound, α–(NH₄)₂Cr₃O₁₀, is reported. The crystal structure has been determined from three dimensional X-ray data collected at low temperature, 173 K. The structure is isomorphous with its Rb and Cs trichromate analogues, orthorhombic, space group Pbca, with a = 11.2558(3), b = 9.3193(3), c = 18.9819(5) ? and Z = 8. The title compound is composed of discrete [Cr₃O₁₀]^2– chains held together by the counter ion charge and a hydrogen bonding network. The different conformations adopted by trichromate anion within its ammonium, alkali and organic salts are discussed.     

Three X-ray diffraction methods for testing of large disk-shaped or lentiform CaF2-crystals for high-performance optics

Three methods (Lang-topgraphy, one-crystal-rocking curves with scan-step-registration, two-crystal-diffractometry (TCD) with a large registered area) were tested. The reached parameters as well as advantages and disadvantages are discussed. The purpose of the examination is the application of CaF₂-crystals with high diameters (⪆ 100 mm) in high-performance optics for the UV-lithography. Especially in this context the influence of defects of the crystal structure on the index of refraction has been examined.     

Pentamethylcyclopentadienylrhodium(I) complexes incorporated into porous polysiloxanes prepared by a sol–gel process: catalysts for hydrogenation of crotonic acid in water

Pentamethylcyclopentadiene‐functionalized polysiloxanes were prepared by a sol–gel process from tetraethoxysilane and (pentamethylcyclopentadienylmethyl)methyldiethoxysilane without a catalyst. The polysiloxanes are microporous–mesoporous solids, of which the BET surface areas and micropore volumes are inversely proportional to the concentration of the functionalizing agent (5–21 mol%) in the starting mixture of alkoxysilanes. The polysiloxanes were also characterized by CP MAS ¹³C NMR spectroscopy, revealing essentially the same structure of organofunctional ligand as that in particulate materials with low surface areas prepared earlier in a sol–gel process catalyzed by dibutyltin diacetate. Novel alkoxysilyl‐substituted pentamethylcyclopentadienyl (1,5‐cyclo‐octadiene)rhodium(I) complexes were synthesized from the corresponding cyclopentadienes by deprotonation followed by reaction with [(cod)RhCl]₂ (cod = cyclo‐octadiene). Polysiloxane‐bound rhodium complexes were prepared by a sol–gel reaction analogous to the one mentioned above and were found to catalyze the hydrogenation of crotonic acid in water; to the best of our knowledge, this constitutes the first example of catalysis by a well‐defined polysiloxane‐bound transition metal complex in an aqueous system. Copyright © 2000 John Wiley & Sons, Ltd.