Large Enhancement of the Single-Molecular Conductance of a Molecular Wire through a Radical Substituent

The single-molecular conductance between two π-conjugated wires with and without a radical substituent has been compared. Specifically, methyl- and iminonitroxide-substituted 4-(biphenyl-4-yl)pyridine wires bound onto a porphyrin template were subjected to scanning tunneling microscopy (STM) apparent-height measurement at the interface between highly oriented pyrolytic graphite (HOPG) and octan-1-oic acid. Statistical analysis of the STM images revealed that the radical-substituted wire has 3.2±1.7-fold higher conductance than the methyl-substituted reference. Although density functional theory (DFT) calculation suggests that only 17 % of the SOMO is distributed on the wire moiety, the effect was significant. This study presents the potential of radical substituents to achieve high conductivity in molecular wires.     

Structures and Reaction Mechanism of Novel Metal-Carbene Complexes Derived from Hypervalent Diazadiselenathiapentalenes

Abstract

Novel metal-carbene complexes (4) with a metallapentalene framework have been obtained from hypervalent diazadiselenathiapentalenes (3) by treating with Pt(PPh₃)₄, Pd(PPh₃)₄ and RhCl(PPh₃)₃. X-Ray investigations revealed that the central hypervalent sulfur atom in 3 was substituted by a metal atom to form M-Se bonds in the resultant metallapentalene framework.     

Total Synthesis of the 7,10‐Epimer of the Proposed Structure of Amphidinolide N,Part II: Synthesis of C17–C29 Subunit and Completion of the Synthesis

The total synthesis of 7,10‐epimer of the proposed structure of amphidinolide N was accomplished. The requisite chiral C17–C29 subunit was assembled stereoselectively via Keck allylation, Shi epoxidation, diastereoselective 1,3‐reduction, and a later oxidative synthesis of the THF framework. The C1–C13 and C17–C29 subunits were successfully coupled using a Enders RAMP “linchpin” as the C14–C16 three carbon unit, thereby controlling the chirality at C14 and C16. The labile allyl epoxy moiety was successfully constructed by Grieco–Nishizawa olefination at a final stage of the synthesis.     

Widely tunable THz synthesizer

The generation of cw-THz radiation by photomixing is particularly suited to the high resolution spectroscopy of gases; nevertheless, until recently, it has suffered from a lack of frequency metrology. Frequency combs are a powerful tool that can transfer microwave frequency standards to optical frequencies and a single comb has permitted accurate (10⁻⁸) THz frequency synthesis with a limited tuning range. A THz synthesizer composed of three extended cavity laser diodes phase locked to a frequency comb has been constructed and its utility for high resolution gas phase spectroscopy demonstrated. The third laser diode allows a larger tuning range of up to 300 MHz to be achieved without the need for large frequency excursions, while the frequency comb provides a versatile link to be established from any traceable microwave frequency standard. The use of a single frequency comb as a reference for all of the cw-lasers eliminates the dependency of synthesized frequency on the carrier envelope offset frequency. This greatly simplifies the frequency comb stabilization requirements and leads to a reduced instrument complexity.     

Synthesis of Au–Pd bimetallic nanoparticles under energetic irradiation fields

Bimetallic Au–Pd nanoparticles were synthesized under high-energy irradiation fields (1.17 and 1.33 MeV γ-rays, 9 MeV electrons, and 1.6 GeV C ions) from solutions containing Au³⁺ and Pd²⁺ and cationic surfactant (sodium dodecyl sulfate). Particles synthesized by the irradiation were observed using conventional transmission electron microscope (TEM) and annular dark-field scanning transmission electron microscopy (ADF-STEM). The particles synthesized by γ-rays and C ion irradiation exhibit core–shell structure with a Au-core and a Pd-shell. The dependence of the size distribution of nanoparticles on the dose rate is discussed.     

Deformation Electron-Density Distributions of Tetraazathiapentalenes with Hypervalent S-N Bonds

Abstract

The deformation electron-density distributions of 6a-thia-1,3,4,6-tetraazapentalene derivatives (I, II) and bis(phenylthio)dibenzothiophene (III) were investigated by the X-ray diffraction method. For I and II, a structure around the hypervalent S-N bonds is a trigonal bipyramid with equatorial sp² hybrid of S-C bond and lone-pair electrons and apical polarized S-N bonds. In 111 lone-pair electron densities are observed perpendicular to the thiophene ring and the C-S-C sulfide planes.