Theoretical study of M(+)-RG complexes (M = Ga, In; RG = He-Rn)

We present potential energy curves calculated at the CCSD(T) level of theory for Ga(+)-RG and In(+)-RG complexes (RG = He-Rn). Spectroscopic parameters have been derived from these potentials and compared to previously calculated parameters for the Al(+)-RG and Tl(+)-RG complexes. Additionally, for some cases, we compare these parameters with those obtained from electronic spectroscopic studies on excited states of the neutral species, arising from atomic-based d ← p excitations. The Ga(+)-RG and In(+)-RG potentials have also been used to calculate the transport coefficients for M(+) traveling through a bath of RG atoms.     

Functionalization of flat Si surfaces with inorganic compounds—Towards molecular CMOS hybrid devices

Covalent modification of flat silicon surfaces is a key step in integrating CMOS technology and molecular electronics that may lead to novel hybrid microelectronic devices. While much of the research has been focused on the functionalization of Si by organic compounds, interest in the functionalization with metal-containing species has intensified in recent years because of the unique attributes of inorganic species including rich redox characteristics and high ground state spins. Described in this short review are (i) synthetic approaches to immobilize inorganic compounds; (ii) structural, spectroscopic and voltammetric techniques for characterization of molecular layers; and (iii) preliminary device fabrication.     

Network Forming Fluids: Yukawa Square-Well <Emphasis Type="Italic">m</Emphasis>-Point Model

Thermal and connectivity properties of the Yukawa square-well m-point (YSWmP) model of the network forming fluid are studied using solution of the multidensity Ornstein-Zernike and connectedness Ornstein-Zernike equations supplemented by the associative mean spherical approximation (AMSA). The model is represented by the multicomponent mixture of Yukawa hard spheres with m_s^am_{s}^{a} square-well sites, located on the surface of each hard sphere. To validate the accuracy of the theory, computer simulation is used to calculate the structure, thermodynamic and connectivity properties of the one-component YSW4P version of the model which is compared against corresponding theoretical data. In addition, connectivity properties of the model were studied using Flory-Stockmayer (FS) theory. Predictions of the AMSA for the thermal properties of the model (radial distribution functions (RDF), internal energy, pressure, fractions of the particles in different bonding states) are in good agreement with computer simulation predictions. Similarly, good agreement was found for the connectedness RDF (CRDF), except for the statepoints located close to the percolation threshold, where the theory fails to reproduce the long-range behavior of the CRDF. Results of both theories (AMSA and FS) for the mean cluster size are reasonably accurate only at low degrees of association. Predictions of the FS theory for the percolation lines are in a good agreement with computer simulation predictions. AMSA predictions of percolation are much less accurate, where corresponding percolation lines are located at a temperatures approximately 25% lower then those calculated using computer simulation.     

Synthesis and Characterization of Poly(Aryl Ether-Bissulfone)s

A series of poly(aryl ether-bissulfone)s were synthesized from bis-phenols, 4,4′-bis(4-chlorophenylsulfonyl)biphenyl, and 4,4′-bis(4-fluorophenylsulfonyl)biphenyl. The bishalide monomers were synthesized by reaction of 4,4′-bis(chlorosulfonyl)biphenyl with a suitable aryl halide. Potassium carbonate mediated reaction in di-methylacetamide gave high molecular weight polymers in excellent yield. The polymers are soluble in dipolar aprotic solvents. Unlike the corresponding monosulfone analogues, the poly(aryl ether-bissulfone)s exhibited poor solubility in chlorinated hydrocarbons. The glass transition temperatures of the polymers are among the highest known for poly(aryl ether)s (241-271 °C). In addition, the polymers exhibit excellent thermal stability and they produce clear, colorless tough films by solution casting or compression molding.     

Microwave Promoted Oxidative Addition Reactions of Os3(CO)12: Efficient Syntheses of Triosmium Clusters of the Type Os3(μ-X)2(CO)10 and Os3(μ-H)(μ-OR)(CO)10

Microwave heating allows for the high-yield, one-step synthesis of the known triosmium complexes Os₃(μ-Br)₂(CO)₁₀ (1), Os₃(μ-I)₂(CO)₁₀ (2), and Os₃(μ-H)(μ-OR)(CO)₁₀ with R = methyl (3), ethyl (4), isopropyl (5), n-butyl (6), and phenyl (7). In addition, the new clusters Os₃(μ-H)(μ-OR)(CO)₁₀ with R = n-propyl (8), sec-butyl (9), isobutyl (10), and tert-butyl (11) are synthesized in a microwave reactor. The preparation of these complexes is easily accomplished without the need to first prepare an activated derivative of Os₃(CO)₁₂, and without the need to exclude air from the reaction vessel. The syntheses of complexes 1 and 2 are carried out in less than 15 min by heating stoichiometric mixtures of Os₃(CO)₁₂ and the appropriate halogen in cyclohexane. Clusters 3–6 and 8–10 are prepared by the microwave irradiation of Os₃(CO)₁₂ in neat alcohols, while clusters 7 and 11 are prepared from mixtures of Os₃(CO)₁₂, alcohol and 1,2-dichlorobenzene. Structural characterization of clusters 2, 4, and 5 was carried out by X-ray crystallographic analysis. High resolution X-ray crystal structures of two other oxidative addition products, Os₃(CO)₁₂I₂ (12) and Os₃(μ-H)(μ-O₂CC₆H₅)(CO)₁₀ (13), are also presented.     

PREPARATION,DERIVATIZATION WITH TRIMETHYLSILYLDIAZOMETHANE,AND GC/MS ANALYSIS OF A “POOL” OF ALKYL METHYLPHOSPHONIC ACIDS FOR USE AS QUALITATIVE STANDARDS IN SUPPORT OF COUNTERTERRORISM AND THE CHEMICAL WEAPONS CONVENTION

There are hundreds of nerve agents in the class of alkyl methylphosphonofluoridates covered by Schedule 1 of the CWC (Chemical Weapons Convention). Hydrolysis of these sarin-like nerve agents results in an equal number of alkyl methylphosphonic acids. These alkyl methylphosphonic acids are persistent and provide good evidence of specific agent production or use. In order to support the CWC and counterterrorism activities, it is desirable to have ready access to each of these hydrolysis products for use as qualitative standards. A means for simultaneously producing multiple alkyl methylphosphonates from methylphosphonic acid and the corresponding alcohols was developed. Derivatization of these alkyl methylphosphonic acids with trimethylsilyldiazomethane yields the corresponding methyl esters which are suitable for GC/MS analysis.     

Halometallate Complexes of Germanium(II) and (IV): Probing the Role of Cation,Oxidation State and Halide on the Structural and Electrochemical Properties

The Ge^IV chlorometallate complexes, [EMIM]₂[GeCl₆], [EDMIM]₂[GeCl₆] and [PYRR]₂[GeCl₆] (EMIM=1‐ethyl‐3‐methylimidazolium; EDMIM=2,3‐dimethyl‐1‐ethylimidazolium; PYRR=N‐butyl‐N‐methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single‐crystal X‐ray diffraction. The imidazolium chlorometallates exhibited significant C?H???Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution ¹H NMR data also showed cation–anion association. The synthesis and characterisation of Ge^II halometallate salts [EMIM][GeX₃] (X=Cl, Br, I) and [PYRR][GeCl₃], including single‐crystal X‐ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic‐voltammetry experiments on the Ge^IV species in CH₂Cl₂ solution showed two distinct, irreversible reduction waves attributed to Ge^IV–Ge^II and Ge^II–Ge⁰, whereas the Ge^II species exhibited one irreversible reduction wave. The potential for the Ge^II–Ge⁰ reduction was unaffected by changing the cation, although altering the oxidation state of the precursor from Ge^IV to Ge^II does have an effect; for a given cation, reduction from the [GeCl₃]^? salts occurred at a less cathodic potential. The nature of the halide co‐ligand also has a marked influence on the reduction potential for the Ge^II–Ge⁰ couple, such that the reduction potentials for the [GeX₃]^? salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.     

Manager-worker-based model for the parallelization of quantum Monte Carlo on heterogeneous and homogeneous networks

A manager-worker-based parallelization algorithm for Quantum Monte Carlo (QMC-MW) is presented and compared with the pure iterative parallelization algorithm, which is in common use. The new manager-worker algorithm performs automatic load balancing, allowing it to perform near the theoretical maximal speed even on heterogeneous parallel computers. Furthermore, the new algorithm performs as well as the pure iterative algorithm on homogeneous parallel computers. When combined with the dynamic distributable decorrelation algorithm (DDDA) [Feldmann et al., J Comput Chem 28, 2309 (2007)], the new manager-worker algorithm allows QMC calculations to be terminated at a prespecified level of convergence rather than upon a prespecified number of steps (the common practice). This allows a guaranteed level of precision at the least cost. Additionally, we show (by both analytic derivation and experimental verification) that standard QMC implementations are not "perfectly parallel" as is often claimed.     

Kinetics and mechanism of light-driven oxygen evolution at thin film α-Fe2O3 electrodes

Rate constants for recombination and hole transfer during oxygen evolution at illuminated α-Fe(2)O(3) electrodes were measured by intensity-modulated photocurrent spectroscopy and found to be remarkably low. Treatment of the electrode with a Co(II) solution suppressed surface recombination but did not catalyse hole transfer. Intermediates in the reaction were detected spectroscopically.     

Diruthenium(III,III) ethynyl-phenyleneimine molecular wires: preparation via on-complex Schiff base condensation

The diruthenium compound trans-Ru(2)(DMBA)(4)(C≡C-C(6)H(4)-4-CHO)(2) (1; DMBA is N,N'-dimethylbenzamidinate) was prepared from the reaction between Ru(2)(DMBA)(4)(NO(3))(2) and HC≡C-C(6)H(4)-4-CHO under the weak base conditions. The aldehyde groups of 1 undergo a condensation reaction with NH(2)C(6)H(4)-4-Y (Y = H and NH(2)) to afford new compounds trans-Ru(2)(DMBA)(4)(C≡C-C(6)H(4)-4-CH═N-C(6)H(4)-4'-Y)(2) (Y = H (2) and NH(2) (3)). A related compound, Ru(2)(DMBA)(4)(C≡C-C(6)H(4)-4-N═C(Me)Fc)(2) (4), was also prepared from the reaction between Ru(2)(DMBA)(4)(NO(3))(2) and HC≡C-C(6)H(4)-N═C(Me)Fc. X-ray structural studies of compounds 1 and 2 revealed significant deviation from an idealized D(4h) geometry in the coordination sphere of the Ru(2) core. Voltammetric measurements revealed four one electron redox processes for compounds 1-3: the Ru(2) centered oxidation and reduction, and a pair of reductions of the imine or aldehyde groups. Compound 4 displays an additional oxidation attributed to the Fc groups. DFT calculations were performed on model compounds to gain a more thorough understanding of the interaction of the organic functional groups across the diruthenium bridge.