Synthesis,structure, and magnetic properties of the fullerene-based ferromagnets Eu3C70 and Eu9C70

Intercalation of C(70) with europium affords two kinds of magnetic compounds, a canted antiferromagnet Eu(x)C(70) (x approximately 3) and a ferromagnet Eu(x)C(70) (x approximately 9) with transition temperatures (T(C)) of 5 and 38 K, respectively. The Curie constants in the paramagnetic phase and the saturation moment in the ferromagnetic phase are both understood by the full moment of Eu(2+) for both systems. The structure of Eu(3)(-)(delta)C(70) (delta approximately 0.27) is pseudo-monoclinic, derived by a simple deformation of the parent face-centered cubic (fcc) structure. Eu(9)(-)(delta)C(70) (delta approximately 0.2) forms an fcc structure, in which cuboctahedral clustering of Eu(2+) ions is observed in the enhanced size octahedral holes. The observed T(C) of the Eu(9)(-)(delta)C(70) ferromagnet is comparable to or larger than those of simple binary Eu-based ferromagnets, such as Eu chalcogenides or carbides, despite the low atomic ratio of Eu in the chemical formulas. This can be understood by the short Eu(2+)-Eu(2+) distances and high coordination numbers permitted by the multiple occupation by Eu(2+) ions of the expanded octahedral interstitial sites in higher fullerene-based solids.     

Synthesis and absorption/emission properties of novel poly(silylenearylenevinylene)s

Polymerization of p-(dimethylsilyl)phenylacetylene in toluene at 25 and 80 °C with RhI(PPh₃)₃ catalyst afforded highly regio- and stereoregular poly(dimethylsilylene-1,4-phenylenevinylene)s [cis- and trans-poly( 1a )s] containing 98% cis- and 99% trans-vinylene moieties, respectively. The trans-type polymers exhibited redshifts and hyperchromic effects in the ultraviolet–visible spectrum as compared with the cis-type counterparts. Photoirradiation of cis- and trans-poly( 1a )s gave cis-rich mixtures at equilibrium states. The trans and cis polymers exhibited different emission properties, for example—trans polymer, emissn λ_max = 400 nm, quantum yield: 3.4 × 10⁻³ and cis polymer, emissn λ_max = 380 nm, quantum yield: 1.5 × 10⁻³. Besides poly( 1a ), poly(dimethylsilylenearylenevinylene)s containing biphenylene and phenylenesilylenephenylene units [poly( 3 )] were prepared. The extent of conjugation in these polymers decreased in the orders of biphenylene > phenylene > phenylenesilylenephenylene as well as trans-vinylene > cis-vinylene. The quantum yield of the trans-rich polymer with biphenylene moiety was fairly large and 0.15. Polyaddition of 1,4-bis(dimethylsilyl)benzene and three types of diethynylarenes (4,4′-diethynylbiphenyl, 2,7-diethynylfluorene, and 2,6-diethynylnaphthalene) catalyzed by RhI(PPh₃)₃ provided novel regio- and stereoregular polymers [poly( 6 )]. These polymers displayed blue light emission with high quantum yields (4–81%). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3615–3624, 2003     

Molecular weight evaluation of poly(dimethylsiloxane) on solid surfaces using silver deposition/TOF-SIMS.

Molecular ions include information about end groups, functional groups and molecular weight. A method for the direct detection of these in the high mass range (m/z > 1000) from poly(dimethylsiloxane) (PDMS) on a solid surface was investigated. It was found that a TOF-SIMS analysis of silver-deposited surfaces (silver deposition/TOF-SIMS) is useful for this purpose. Using the silver-deposition/TOF-SIMS method, silver-cationized quasi-molecular ions were clearly detected from PDMS on solid surfaces, and their structure and molecular weight were evaluated. In addition, their images were observed without the interference of deposited silver. By applying to the analysis of paint defects etc., it was confirmed that this technique is useful to analyze actual industrial materials. Silver-cationized ions were detected not only from PDMS, but also from other organic materials, such as lubricant additives and oils on solid surfaces. Therefore, the silver deposition/TOF-SIMS method was proved to be useful for the analysis of ultrathin substances on solid surfaces.     

A Comparison Between James and von Neumann–Jordan Constants

In this paper, we compare James and von Neumann–Jordan constants of normed spaces under certain conditions. It is shown that if a normed space with James constant \(\sqrt{2}\) is three- or more dimensional, or is a \(\pi /2\)-rotation-invariant two-dimensional space, then its von Neumann–Jordan constant is less than or equal to \(4-2\sqrt{2}\).     

An application of computer image-processing and film replica technique to a nickel foil strain gage

The elastic stress of a specimen subjected to repeated loads is measured by a microscopic observation of slip-bands in nickel foil bonded to the surface of the specimen. The relation between the stress amplitude and the density of slip-bands in the foil is examined at various temperatures. An image-processing system using a personal computer is applied for an automatic measurement of the density of slip-bands in the bonded foil. The density of slip-bands replicated in a plastic film is also measured by the imageprocessing system, and it is in good agreement with the density of the original slip-bands. The peak stresses in grooved shafts under bending are measured using the nickel foil gage and the image-processing system. It is found that the results are satisfactority accurate.     

Lewis Acid Catalyzed Ring‐Opening Reactions of Sugar‐Derived Semicyclic N,O‐Acetals

N‐(Alkoxycarbonyl)‐N‐glycosides (polyoxygenated semicyclic N,O‐acetals) were efficiently synthesized from regular acetyl or methyl glycosides (glucopyranoside, ribofuranoside, arabinofuranoside, and 2‐deoxyribofuranoside) and a carbamate by treatment of trimethylsilyl trifluoromethanesulfonate and 4 Å molecular sieves. It was found that these N‐glycosides underwent Lewis acid catalyzed ring‐opening reactions with silylated nucleophiles to give ring‐opened amino alcohols with good‐to‐high diastereoselectivity. The reactivity order, 2‐deoxyribofuranoside > arabinofuranoside > ribofuranoside > glucopyranoside, was revealed. Ring‐opening reductions were also investigated with silanes or diisobutylaluminium hydride. An appropriate reducing agent was found to be dependent on the N‐glycosides used. A glycosidase inhibitor, (2S,3R,4R)‐2‐hydroxymethylpyrrolidine‐3,4‐diol ( 7 ) was synthesized by means of the reactions.     

Inverted meso-aryl porphyrins with heteroatoms; characterization of thia, selena, and oxa N-confused porphyrins.

Synthesis and characterization of inverted porphyrins containing S, Se, and O are reported. A simple 3 + 1 MacDonald-type condensation using modified tripyrrane containing the N-confused ring and diols afforded various N-confused porphyrins 6a-f in 19-30% yield. The single-crystal X-ray structure of 6b shows a ruffled conformation with tilt angles of 21.11 degrees and 31.23 degrees for the N-confused ring and the adjacent pyrrole ring III, respectively, revealing its severe nonplanarity. Significant changes in C alpha-C beta, C beta-C beta, and C alpha-X bond lengths are observed in 6b relative to free thiophene and pyrrole, suggesting the altered delocalization pathway in the modified N-confused porphyrins. The two molecules in the unit cell show a cyclophane-type noncovalent dimer with a face to face orientation of two N-confused pyrrole rings as a result of the presence of weak N-H...N and C-H...N intermolecular hydrogen bonds involving pyrrole-NH, the N atom of the N-confused ring, and the C atom of the pyrrole ring. A detailed 1H and 13C NMR study by 1D and 2D methods allowed assignments of all the peaks in the free base and protonated forms. NMR studies reveal the presence of three different tautomeric forms in solution for 6c in CDCl3 at low temperature. UV-visible studies reveal absorption band shifts upon heteroatom substitution, and the magnitudes of these shifts are dependent on the nature of the heteroatom. In all cases both monoprotonated and diprotonated species have been identified, and on addition of acid, the first proton goes to the outer N2 atom of the N-confused ring.     

13C Chemical shifts and conformational equilibria in quaternary piperidinium salts

Carbon-13 nuclear magnetic resonance spectra of a series of N-methyl-N-alkylpiperidinium salts have been measured, and the observed chemical shifts analysed in terms of the stereochemical and conformational properties of the molecules. Furthermore, the differences of the free energy (ΔG°) between two conformers on ring inversion have been estimated.