Influence of off-set energy on the electrical characteristics of Si resonant tunneling MOST (SRTMOST)

The effects of the off-set energy between the dielectric films which are formed at the both edges of the channel and the Si substrate on the electrical characteristics are examined for the Si resonant tunneling MOST (SRTMOST). The barrier height of the dielectric films has a great influence on the operation of the SRTMOST. The relationship between the transmission coefficient and the off-set energy of the double barrier/Si is calculated as well as the relationships between the gate-off currents, the transition time from the source to the drain and the off-set energy. It was found that the critical off-set energy of dielectric film/Si is approximately 1.0–1.5 eV.     

Synthesis of various 6-substituted 1,4,5,6-tetrahydropyridazines by substitution of a 1,4,5,6-tetrahydro-6-tosylhydrazinopyridazines

1,4,5,6-Tetrahydro-1-tosyl-6-tosylhydrazinopyridazines were prepared by reaction of a 1,4-ketoaldehyde with two equivalents of tosylhydrazine. Thus-obtained hydropyridazines were utilized as a substrate for synthesis of various 1,4,5,6-tetrahydropyridazine derivatives by activation with a Lewis acid, and various nucleophiles reacted to give the corresponding 6-substituted 1,4,5,6-tetrahydropyridazine derivatives. Self-reaction of a 1,4,5,6-tetrahydro-6-tosylhydrazinopyridazine in the presence of 0.5 equivalent of titanium tetrachloride gave a 1,4,5,6-tetrahydropyridazine bearing a pyrrole ring at the 6-position.     

Crystal structures and phase behaviour of acetaldehyde-d4: a study by high-resolution neutron powder diffraction and calorimetry

High-resolution neutron powder diffraction is particularly suited for structure solution and refinement of low-melting point organic crystals of moderate complexity. Here we present the ab initio structure solution and refinement of stable-phase and metastable-phase perdeuterated acetaldehyde (m.p.: 151 K). In the stable phase, the molecule crystallises in the space group P2₁/c (no. 14) with a=3.9069(1) Å, b=5.4224(1) Å, c=12.1868(1) Å, β=94.2970(2)° at 5 K, Z=4. In the metastable phase, the molecule crystallises in the space group Pna2₁ (no. 33) with a=5.1973(1) Å, b=6.9791(1) Å, c=6.9712(1) Å at 5 K, Z=4. The metastable to stable phase transition is characterised by heat capacity measurements.     

Two pressure-induced superconducting anion radical salts exhibiting different spin states at ambient pressure

Pressure-induced superconducting behavior was found in two anion radical salts, EtMe3Z[Pd(dmit)2]2 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate, Z = P, As), that are Mott insulators and exhibit different magnetic and structural transitions at ambient pressure.     

Sharing orbitals: ultrafast excited state deactivations with different outcomes in bucky ferrocenes and ruthenocenes

We report on the singlet ground and singlet/triplet excited-state features of a series of bucky ferrocenes, bucky ruthenocenes, and respective reference compounds. In the bucky ferrocene conjugates, intimate contacts between the fullerenes and ferrocenes result in appreciable ground-state interactions-suggesting a substantial shift of charge density from the electron donor (i.e., ferrocene) to the electron acceptor (i.e., fullerene). In contrast, no prominent charge-transfer features were observed for the bucky ruthenocene conjugates. An arsenal of experimental techniques, ranging from fluorescence (i.e., steady state and time-resolved) and pump probe experiments (i.e., femtosecond and nanoseconds) to pulse radiolysis, were employed to examine excited-state interactions. In the excited states, bucky ferrocene conjugates are dominated by rapid charge separation reactions (0.8 +/- 0.1 ps) to yield metastable radical ion pairs. The radical ion pair lifetimes vary between 27 and 39 ps. No charge separation was, however, found in the corresponding bucky ruthenocence. Instead, an intrinsically faster excited-state deactivation (approximately 200 ps) evolves from the heavier ruthenium center-relative to iron. This effect is further augmented by the unfavorably shifted oxidation potential in ruthenocene of about 0.61 V, which in ruthenocene (-deltaG(ET) = -0.26 eV), in contrast to ferrocene (-deltaG(ET) = 0.35 eV), renders charge separation thermodynamically unfeasible.     

Synthesis and electrochemistry of double-decker buckyferrocenes

D5d- and C5v-symmetric double-decker buckyferrocene Fe2(C60R10)Cp2 (R10 = Me5Ph5 and Me10) represents a new type of diiron complexes featuring conjugative connection of two ferrocene groups by a hoop-shaped [10]cyclophenacene. The compounds exhibit two-electron oxidation and two-electron reduction behavior, generating dicationic and dianionic species. The two iron atoms interact with each other through the pi-conjugation of the cyclophenacene, as revealed by differential pulse voltammetric analysis of the D5d Fe2(C60Me10)Cp2.     

Starting point to molecular design: efficient automated 3D model builder Key3D

Obtaining three-dimensional (3D) structures from structural formulae is a crucial process in molecular design. We have developed a new 3D model builder, Key3D, in which the simplified distance geometry technique and structure optimization based on the MMFF force field are combined. In an evaluation study using 598 crystal structures, the high performance and accuracy of Key3D were demonstrated. In the "flexible-fitting" test, which is focused on practical usefulness in the molecular design process, 88% of the Key3D structures acceptably reproduced the reference crystal structures (root-mean-square deviation <0.6 A) upon rotation of acyclic bonds. These results indicate that Key3D will be very effective in providing starting points for practical molecular design.     

Synthesis and spectroscopic properties of platinum(II) terpyridine complexes having an arylborane charge transfer unit

Synthesis, redox, spectroscopic, and photophysical properties of a new class of Pt(II) complexes of the type [PtLnCl]+ are reported, where Ln is 4'-phenyl(dimesitylboryl)-2,2':6',2"-terpyridine (L1) or 4'-duryl(dimesitylboryl)-2,2':6',2"-terpyridine (L2). The free L1 or L2 ligand in CH3CN shows the absorption band responsible for intramolecular charge transfer (CT) from the pi-orbital of the aryl group in L1 or L2 (pi(aryl)) to the vacant p-orbital on the boron atom (p(B)), in addition to pipi* absorption in the 2,2':6',2"-terpyridine (tpy) unit. In particular, the L1 ligand shows an intense CT absorption band as compared with L2. Such intramolecular pi(aryl)-p(B) CT interactions in L1 give rise to large influences on the redox, spectroscopic, and photophysical properties of [PtL1Cl]+. In practice, [PtL1Cl]+ shows strong room-temperature emission in CHCl3 with the quantum yield and lifetime of 0.011 and 0.6 micros, respectively, which has been explained by synergetic effects of Pt(II)-to-L1 MLCT and pi(aryl)-p(B) CT interactions on the electronic structures of the complex. In the case of [PtL2Cl]+, the dihedral angle between the planes produced by the tpy and duryl(dimesitylborane) groups is very large (84 degrees ) as compared with that between the tpy and phenyl(dimesitylborane) units in [PtL1Cl]+ (26-39 degrees ), which disturbs electron communication between the Pt(II)-tpy and arylborane units in [PtL2Cl]+. Thus, [PtL2Cl]+ is nonemissive at room temperature. The important roles of the synergetic CT interactions in the excited-state properties of the [PtL1Cl]+ complex are shown clearly by emission quenching of the complex by a fluoride ion. The X-ray crystal structure of [PtL1Cl]+ is also reported.     

A mild and convenient synthesis of N-carbobenzyloxy ketimines

N-Carbobenzyloxy (Cbz) ketimines were prepared conveniently from N-Cbz amines by oxidation with N-tert-butylbenzenesulfinimidoyl chloride.     

Mild preparation of alkenes from phenyl sulfides: one-pot elimination of phenylthio group via sulfilimine at ambient temperature

[Structure: see text] Various alkenes were prepared from phenyl sulfides in a one-pot manner at room temperature by converting them to the corresponding S-aminosulfonium salts with O-mesitylenesulfonylhydroxylamine, followed by treatment with potassium carbonate. Alkenes were formed by cis-elimination of in situ generated phenyl sulfilimines.