Pentacoordinated tin(II); crystal structure of dichloro-[2,2′∶6′,2″-terpyridyl]-tin(II)

The crystal structure of a well-defined 5-coordinate complex, dichloro-(2,26, 2-terpyridyl)-tin(II), is described. The stereochemistry of this complex is strongly influenced by the stereochemically active pair of electrons, illustrating clearly the potential donor capabilities of this molecule. The complex (C₁₅H₁₁Cl₂N₃Sn) crystallizes in the monoclinic space groupC2/c (No. 15) witha=15.770(5),b=9.450(2),c=10.482(2) Å,=97.53(2)°,Z=4. The finalR value is 0.029 for 1085 observed reflections.     

Bis(N,N′-disalicylidene-3,4-phenylenediamine-1-ethylbenzoato)zirconium(IV), an eight-coordinate chelate with linear polymerization possibilities

Synthesis of the Schiff-base complex bis(N,N′-disalicylidene-3,4-phenylenediamine-1-ethylbenzoato)zirconium(IV), which has two, linearly disposed, uncoordinated ester groups, has been accomplished from the reaction of a zirconium alkoxide with the new Schiff ligand N,N′-disalicylidene-3,4-phenylenediamine-1-ethylbenzoate. The ligand itself was isolated in two forms, yellow and orange, which are believed to be tautomers based on infrared data. Elemental analyses, IR, NMR, and UV-Visible data are included for all new compounds, as well as mass spectral data for the complex. Broadening of ¹H NMR resonances in the complex spectrum, relative to TMS and ethanol of solvation resonances, may be indicative of a slow molecular motion. Preliminary attempts to polymerize the complex with aromatic amines failed, however, due to decomposition of the metal chelate unit at the high temperatures (300°C) required.     

Alkaloid studies—XXX Isolation and constitution of three new Aspidosperma alkaloids: Cylindrocarpine, cylindrocarpidine and pyrifolidine

The isolation and structure elucidation of three new Aspidosperma alkaloids is reported. Cylindrocarpine (II) and cylindrocarpidine (XI) are noteworthy in that they represent analogs of aspidospermine (I) in which the latter's angular ethyl group has been replaced by an angular acetic acid methyl ester function. Furthermore, cylindrocarpine (II) represents the first naturally occurring dihydroindole with a N-cinnamoyl residue. Pyrifolidine (XII) has been shown to be the antipode of O-methylaspidocarpine (XV) and thus bears an enantiomeric relationship at all four asymmetric centers to (-)-aspidospermine (I). Attention is drawn to the possible biogenetic implications of this observation.     

The boat conformation of α-parachloral. Notes on the revised structures of α- andβ-parachloral

The boat conformation of-parachloral [2,4,6-tris(trichloromethyl)-1,3,5-trioxane] has been confirmed by X-ray crystallography. Evidence for a chair conformation based upon calculations of dipole moments has been shown to be unreliable, but the possibility of this existing in solution has been studied by¹H and¹³C NMR spectroscopy. The X-ray structures of both- and-parachloral have been redetermined.     

A liquid derivative of 12-tungstophosphoric acid with unusually high conductivity

Surface functionalization of the solid heteropolyacid H3PW12O40 with a bulky PEG-containing quaternary ammonium cation through partial proton exchange leads to a polyoxometalate-based liquid salt with high-temperature proton conductivity ( approximately 10-3 S cm-1 at 140 degrees C) under dry conditions. The proton conductivity of the liquid salt is 4 orders of magnitude higher than that of the solid analogue under identical conditions and shows super ionic behavior as defined by Walden plot.     

Differential constitutive equation for entangled polymers with partial strand extension

Beginning with a formal statement of the conservation of probability, we derive a new differential constitutive equation for entangled polymers under flow. The constitutive equation is termed the Partial Strand Extension (PSE) equation because it accounts for partial extension of polymer strands in flow. Partial extensibility is included in the equation by considering the effect of a step strain with amplitude E on the primitive chain contour length. Specifically, by a simple scaling argument we show that the mean primitive chain contour length after retraction is L=L ₀ E ^1/2, not the equilibrium length L ₀ as previously thought. The equilibrium contour length is infact recovered only after a characteristic stretch relaxation time λ _s that is bounded by the reptation time and longest Rouse relaxation time for the primitive chain. The PSE model predictions of polymer rheology in various shear and extensional flows are found to be in good to excellent agreement with experimental results from several groups. Received: 16 July 1997 Accepted: 22 January 1998     

Direct sum decomposition of geometries based on maximal subgroups

In 1961 J. Tits described a way to define a geometry from a group and a collection of subgroups. Such incidence geometries are now studied by the team of F. Buekenhout in Brussels. Here we present theorems about decomposition of PRI geometries into direct sums and we find the full direct sum decomposition of PRI geometries on solvable groups.     

Interfacial friction of thin PDMS network films

This study focuses on developing dry, surface‐tethered polymeric lubricant coatings capable of significantly decreasing friction and wear of nano‐ and micrometer scale machines. Vinyl‐terminated polydimethylsiloxane chains are spin‐coated with a crosslinking agent and platinum catalyst onto silicon wafers functionalized with a self‐assembling monolayer containing reactive vinyl groups. Lateral force microscopy (LFM) measurements employing a bead probe are used to quantify the coefficient of friction (COF) and adhesion characteristics of the PDMS‐SAM surface tethered networks. The combined polymer network and SAM layer manifest extremely low friction coefficients, μ = 4 × 10^?3, which is nearly one order of magnitude lower than the friction coefficient of the bare silicon substrate. The lowest friction forces are measured using silicon substrates covered with nanometer thick, peroxide crosslinked PDMS networks; though poorly crosslinked, these networks display COFs as much as ten‐times lower than a solitary SAM coating layer. Micrometer thick end‐linked optimal networks also manifest attractive interfacial friction properties, with COFs approximately three times larger than the thinner, imperfect networks. These observations are discussed in terms of the structure of the polymer networks and the role of adhesion forces on interfacial friction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1773–1787, 2008