Crystal structure of decacalcium tetrapotassium hexakis (pyrophosphate) nonahydrate

The crystal structure of Ca₁₀K₄(P₂O₇)₆·9H₂O has been determined by single crystal X-ray diffraction. Crystals are hexagonal, space group P6₃cm witha=11.761(1),c=9.770(1) Å, andZ=1. The structure was refined toR=0.028 andR _w=0.037 for 468 reflections withI3(I). The structure consists of a compact assembly of Ca and P₂O₇ ions arranged in layers perpendicular to thec-axis in a hexagonal array with relatively large open channels along thec-axis. The K ions and the water molecules are located in these open channels and are disordered.Certain commercial materials and equipments are identified in this paper to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Institute of Standards and Technology or the ADA Health Foundation or that the material or equipment identified is necessarily the best available for the purpose.     

Crystal structure of calcium adipate monohydrate

The crystal structure of calcium adipate monohydrate, Ca(C₆H₈O₄)·H₂O, has been determined by single crystal X-ray diffraction study. The crystals are triclinic witha=5.8990(3),b=6.7985(5),c=10.8212(6)Å,=78.999(5),=81.831(5), and =82.971(5)°, space group P¯1,Z=2,V=419.65(8)ų,d _m=1.59,d _c=1.600 Mg m^–3. The structure was refined by full-matrix least-squares techniques toR=0.040,R _w=0.058 for 1283 reflections withI3(I). Ca is coordinated to seven oxygen atoms and the coordination polyhedron is best described as pentagonal bipyramid. The coordinations of the two carboxylate groups in adipate ion are quite different. One carboxylate group binds three different Ca ions forming a four-membered chelate ring with one Ca ion and unidentate bridge bonds to two other Ca ions. The other carboxylate group links to two Ca ions through unidentate bonds. The structure is highly polymeric, but with a layertype structure parallel to (001) with the hydrocarbon chains sandwiched between the polar regions consisting of Ca, carboxylate and water molecules.Certain commercial materials and equipment are identified in this paper to specify the experimental procedure. In no instance does such identification imply recommendation or endorsement by the National Institute of Standards and Technology or the ADA Health Foundation or that the material or equipment identified is necessarily the best available for the purpose.     

Copper(II) tetrafluroborate-promoted Meinwald rearrangement reactions of epoxides

Epoxides undergo a highly efficient Meinwald rearrangement in the presence of catalytic quantities of copper(II) tetrafluoroborate to give carbonyl compounds in high yields and with excellent selectivity. The low toxicity and ease of handling of this reagent make it an attractive alternative to the more corrosive or costly Lewis acids frequently employed.     

Metal complexation of crosslinked polyacrylamide-supported dithiocarbamates: Effect of the molecular character and extent of crosslinking on complexation

Dithiocarbamate functions were incorporated into different polyacrylamide matrices crosslinked with a flexible and hydrophilic crosslinking agent, tetraethyleneglycol diacrylate (TEGDA), and their complexation behaviours were investigated. Crosslinked polyacrylamides with varying extents of the tetrafunctional TEGDA crosslinks were prepared by free radical solution polymerization at 60°C using potassium persulphate as initiator in ethanol. The dithiocarbamate functionality was incorporated into these polyacrylamides by a two-step polymer-analogous reaction involving (i)trans-amidation with ethylenediamine and (ii) dithiocarbamylation of the aminopolyacrylamide with carbon disulphide and alkali. The complexations of dithiocarbamate with Cu(II), Ni(II), Zn(II), Co(II) and Hg(II) ions were followed under different conditions. The metal ion intake varied with the extent of the crosslinking agent and the observed trend in complexation is Hg(II) > Cu(II)> Zn(II)> Co(II)> Ni (II). The time-course of complexation, the possibility of recycling, swelling characteristics, and spectral and thermal analyses were carried out. The thermal stability increases upon complexation with metal ions.     

Thermolysis reaction of 2-acetyl-1-oxo-five-, six-, and seven-membered ring

The rates of gas-phase thermolysis reactions of 2-acetylcyclopentanone 1,2-acetylcyclohexanone 2, N-acetylcaprolactam 3,2-acetylbutyrolactone 4,2-acetyl-2-methylbutyrolactone 5, and 3-acetyl-2-oxazolidinone 6 have been measured over a temperature range of 50 K. They undergo unimolecular first-order elimination reactions for which log A = 11.7, 11.7, 11.2, 11.4, 11.5, and 11.1 s^?1 and E_a = 193.4, 189.5, 153.2, 201.0, 206.8, and 176.1 kJ mol^?1, respectively. The effect of the ring size together with the effect of a heteroatom in the ring on the rate of thermolysis reactions for compound 1–6 is the subject of this work. © 1995 John Wiley & Sons, Inc.     

Investigating the topochemical polymerization of aniline derivatives in Pb(II) borate scaffolds

Three different aniline derivatives, namely m- and p-aminobenzoic acids and m-amino benzenesulfonic acid, were sequestered in between layers of a borate-based coordination polymer, based on lead(II) tetrakis(imidazolyl)borate. The aniline derivatives pre-organized in the interlayer spacing of the coordination polymer, and the reactivity of these pre-organized anionic monomers in the crystalline state was studied. We found that thermally activated reactivity under ambient atmospheric oxygen promotes what appears to be polymerization, and that the most reactive species is m-aminobenzenesulfonic acid monomer due to its increased mobility within the layers of the polymer.     

Computational study of pharmacophores: beta-sultams

The strain and resonance energies in beta-sultam derivatives have been calculated by using a high-level ab initio method (G3/B3LYP) in order to resolve the question of the principal driving force affecting solvolysis of these new antibiotics. We found that only the combined effect of stabilizing (via amide or sulfonamide resonance interactions) and destabilizing (ring strain) influences can account for the observed rates of solvolysis in beta-lactams and beta-sultams.