O-[(Triorganostannyl)methyl] derivatives of 1,2-O-isopropylidene-α-D-xylofuranose

The synthesis, mass, IR and NMR spectra of 3-O-benzyl-1,2-O-isopropylidene-5-O-[(triphenylstannyl)methyl]--D-xylofuranose (9) and 1,2-O-isopropylidene-3-O-(R₃SnCH₂)-5-O-triphenylmethyl--D-xylofuranose (10, R=Bu or Ph) are reported, as is the X-ray structure of10 (R=Ph). Compound10 (R=Ph), crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4), witha=11.006(4) Å,b=17.096(6) Å,c=21.164(7) Å. The conformation of the furanose ring in solid10 (R=Ph) is a 8218 mixture of the envelope (E₄) and twist (³T₄) forms: the isopropylidene ring conformation is similarly a mixture of envelope and twist forms, with the former dominant. On dissolution, the furanose ring of10 (R=Ph) undergoes a conformation change, with the³T₂ conformation becoming the major form. The tin center in10 is four-coordinate and has a tetrahedral geometry.     

The disordered structure of (p-tolythiomethyl)triphenylgermanium

The disordered crystal structure of Ph₃GeCH₂SC₆H₄Me has been determined in space groupC2/c with cell dimensionsa=16.916(8),b=11.110(8),c=24.217(16)Å, and -98.86(2)°. The structure can be represented by two overlapping images which are only partially resolved. The germanium atom is in a distorted tetrahedral environment and refinement converged atR=0.049. The crystal structure of a similar organogermanium compound, Ph₃GeCH₂SO₂C₆H₅, which crystallizes in space group Cmca witha=11.037(2),b=17.077(3), andc=23.016(6)Å, is also shown to be highly disordered.     

The effect of the H2O/TEOS ratio on the structure of gels derived by the acid catalysed hydrolysis of tetraethoxysilane

Silica gels were produced by the acid catalysed hydrolysis of tetraethoxysilane (TEOS) using H₂O/TEOS ratios from 2 to 50. After heat treatment the structure of the gels was studied using nitrogen adsorption, small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and bulk density measurements.All the gels possessed microporosity in the region of 30 Å or less. For H₂O/TEOS = 25 and 50 the matrix density was found to be uniform, but for gels from solutions with H₂O/TEOS = 2,4 and 10, density fluctuations in the matrix were detected from Porod analysis of the SAXS data. These results indicate that in higher water content solutions, rearrangement of the polymeric chains leads to small densified particles, but for lower water content solutions, gelation results from the entanglement of linear chains leaving free volume on a molecular scale between the chains.     

Structure of chlorotris(1,3,5-triaza-7-phosphaadamantane)platinum(II) chloride hydrate methanolate, [Pt(PTA)3Cl] [Cl]·H2O·CH3OH

The title compound chlorotris(PTA)platinum(II) chloride hydrate methanolate (PTA=1,3,5-triaza-7-phosphaadamantane), [C₁₉H₄₂Cl₂N₉O₂P₃Pt] is monoclinic, witha=10.832(1),b=21.306(7),c=12.702(3)Å,=100.42(5)°,V=2883(2)ų,Z=4,D _x=1.814 g cm^–3,=53.0 cm^–1,F(000)=1568,T=298K in space groupP2₁/c. The structure was solved by heavy atom and Fourier methods and refined toR=0.051 for 4319 unique observed reflections. The complex exhibits approximately square-planar geometry about the Pt atom and a significant trans effect, with bond lengths Pt-Cl1=2.3371(2), Pt-C12 (ionic)=4.463(4), Pt-P _{trans(to cl)}=2.233(2), Pt-P _cis,ave=2.323(3)Å and bond angles Cl-Pt-P _cisave 83.60(3), P _trans -Pt-P _cis,ave 96.49(6)°. The H₂O is apparently hydrogen bonded to two N atoms on different cations, and the methanol OH group to the chloride anion.     

Crystal and molecular structure of 3,3-diphenyl-3-phosphoniabicyclo[3.2.1]oct-6-ene bromide monohydrate

The title compound crystallizes in the monoclinic space groupP2₁/n,a=13.429(3),b=18.248(6),c=14.497(4)Å,=90.61(2)°,Z=8, with two independent molecules in the asymmetric unit. The structure was solved by heavy-atom methods, and refined to a finalR value of 0.040. The phosphoranium ring adopts a chair conformation which is substantially flattened at the phosphorus end. The ring conformation and torsion angles are compared with similar compounds.     

The low-temperature specific heat of PTFE (Teflon) at pressures to 5.2 kbar

The specific heat of PTFE (Teflon) has been measured between 0.3 and 20 K at zero pressure, and between 1 and 20 K at five other pressures ranging up to 5.2 kbar. The specific heat anomalies typical of amorphous materials were observed. The linear term is smaller than for other organic polymers and is closer in magnitude to those of high purity glassy insulators. At zero pressure the T³ term in the specific heat exceeds that calculated from the sound velocities by 24%. The evolution with pressure of the T³ term and of the maximum in C/T³ are very similar, suggesting a close relation between the vibrational modes that contribute to these features in the specific heat. This result and the relatively simple structure of Teflon rule out independent localized oscillators as the source of the maximum in C/T³.     

Caging the mercurous ion: a tetradentate tripodal nitrogen ligand enhances stability and J(1H199Hg)

The dimeric mercurous ion has been encapsulated by a pair of the tetradentate tripodal nitrogen ligands tris[(2-(6-methylpyridyl))methyl]amine (TLA). The complex [Hg₂(TLA)₂](ClO₄)₂ (1) was isolated directly from an acetonitrile solution of Hg(ClO₄)₂ 3H₂O and TLA. Complex 1 crystallizes in the triclinic space group with a = 10.537(2) Å, b = 10.751(2) Å, c = 10.907(2) Å, = 75.20(3), = 73.73(3), = 75.73(3), and Z = 1. The cation is located an inversion center. The Hg–Hg and Hg–N_amine bond distances are 2.5469(8) and 2.297(6) Å, respectively, and the average Hg–N_pyridyl bond length is 2.75(7) Å. Complex 1 was stable indefinitely in acetonitrile-d ₃ solution, permitting detection of 13 and 22 Hz heteronuclear couplings between the Hg(I) ions and the methylene protons of the ligand. Comparisons with the structures and spectroscopic properties of related mercuric and mercurous complexes are made.     

Structure of {Pb[S2CN(C2H5)2]2(1,10-phenanthroline)}2

Lead (II) nitrate reacts with 1,10-phenanthroline and sodium diethyldithiocarbamate in water to produce yellow bisdiethyldithiocarbamata 1,10-phenanthroline lead(II). Crystals from water are triclinic, space group $P\bar 1$ (#2),a=10.53(2) Å,b=11.050(12)Å,c=24.74 (3) Å, α=94.71 (9)⁰, β=98.15(11)^o, γ=114.11(9)^o,V=2569(6) ų,Z=2. Each lead atom has approximate pentagonal pyramid coordination geometry through the nitrogens of a phenathroline and sulfurs of two dithiocarbamates. Additionally, complexes form loose dimers in which lead atoms are weakly coordinated to a sulfur in an adjacent complex. IR and proton nmr spectrum of the complex are consistent with the solid state structure.     

The dielectric constant and salt effects upon the acid hydrolysis of methyl propionate

The hydrolysis of methyl propionate catalyzed by hydrochloric acid has been studied at three temperatures in water-acetone media and in water media containing different concentrations of sodium nitrate. The specific velocity constants in wateracetone media were shown to conform to the theory for reaction between positive ions and dipolar molecules. bender's mechanism for ester hydrolysis has been accepted as plausible in view of the kinetics in mixed media. The specific velocity constants in the sodium nitrate solutions were shown to conform to the theory of Euler.     

Polarographic determination of aluminum in titanium alloys

Considerable interest has been shown in titanium metal because of its combination of desirable properties, including its favorable strength to weight ratio and its resistance to corrosion. Since titanium-aluminum alloys are fairly common, there is need for an accurate method of determining aluminum over a wide range of concentrations. This paper describes an accurate and fairly rapid polarographic method for determining aluminum based on the reduction of an aluminum-azo dye complex after removing titanium, and other interferences by cupferron precipitation, followed by electrolysis at a mercury cathode when necessary. The reduction takes place at — 0.44 volt versus the saturated calomel electrode in a solution buffered at pH 4.6 with acetate. The method is sensitive from 0.01 mg to 0.50 mg of aluminum per 50 ml, covering a range of 0.005 to 10.0 per cent aluminum.