Are terminal aryl butadiynes stable? Synthesis and X-ray crystal structures of a series of aryl- and heteroaryl-butadiynes (Ar-CC-CC-H)

The synthesis and isolation are reported of a range of terminal aryl- and heteroaryl-butadiynes (ArCC-CCH) 4a-h from 2-methyl-6-(aryl/heteroaryl)hexa-3,5-diyn-2-ol precursors. The stability of 4a-h in solution is concentration dependent: many of the derivatives can be stored as dilute solutions for several days or even weeks. The X-ray crystal structures have been obtained for five ArCC-CCH derivatives [Ar = 2-(9-fluorenonyl), 4-biphenyl, 2-pyridyl, 4-pyridyl, and 2-pyrazyl].     

Synthesis, characterization and thermal properties of cobalt(II), nickel(II) and copper(II) complexes of 2,6-bis(3,4,5-trimethyl-N-pyrazolyl)pyridine): the crystal structure of [Co(btmpp)(H2O)2(NO3)]NO3

Co(II), Ni(II) and Cu(II) nitrate complexes with btmpp, namely ([Co(btmpp)(H₂O)₂(NO₃)]NO₃ (1), [Ni(btmpp)(H₂O)(NO₃)]NO₃ (2) and [Cu(btmpp)(MeOH)(NO₃)]NO₃ (3), where btmpp = 2,6-bis(3,4,5-trimethyl-N-pyrazolyl)pyridine), have been synthesized and characterized by physicochemical and spectroscopic methods. The crystal structure of complex 1 has been determined by single crystal diffraction at 100K. In all the complexes, btmpp is coordinated in a tridentate mode through its nitrogen atoms. One of the nitrates in complex 1 is terminally bonded to the metal center through the oxygen atom, whereas the other one is out of the coordination sphere. The Co(II) atom in complex 1 is hexa-coordinated with a CoN₃O₃ distorted octahedral environment. Decomposition of three complexes was analyzed thermogravimetrically. All three complexes decompose similar to explosive material.     

Kinetic study of the reaction of dimethyl carbonate with trialkylamines

Quaternary ammonium compounds are produced worldwide in hundreds of millions of pound volume annually for a plethora of end‐uses from fabric‐care formulations to asphalt emulsifiers, typically from nongreen alkylating reagents. The kinetics of a reaction employing dimethyl carbonate (DMC) as a green alkylating agent was investigated using three trialkylamines (tributylamine, trihexylamine, and trioctylamine) at several temperatures. Arrhenius and Eyring analysis of the data showed that values of E_a (79 kJ/mol), ΔH^? (75 kJ/mol), and ΔS^? (220 J/(mol K)) were the same for all three amine reactants, consistent with a report that E_a is independent of alkyl chain length when the chain length is greater than three carbons. Although rates are significantly slower with DMC than with other alkylating reagents, the resulting methyl carbonate anion has advantages for clean anion metathesis, which is important for some applications, especially those involving ionic liquids. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 221–225, 2010     

Experimental and computational investigations of a cadmium(II) mononuclear complex with 2,6-Bis(3,5-dimethyl-N-pyrazolyl)pyridine (bdmpp) and selenocyanate as ligands

A new cadmium (II) complex, [Cd(bdmpp)(SeCN)₂(H₂O)] (1) (where bdmpp = 2,6-bis(3,5-dimethyl-N-pyrazolyl)pyridine), has been synthesized and characterized by elemental and spectral (IR, ¹H-NMR and ¹³C-NMR, UV-Vis) analyses, differential scanning calorimetry, and single crystal X-ray diffraction studies. X-ray analysis showed that the structure was crystallized in the monoclinic space group Cc with a = 9.031(2), b = 13.884(3), c = 16.910(3) Å, and Z = 4. The geometry around the cadmium atom is distorted octahedral with a CdN₃Se₂O setup. The N atoms of the SeCN are engaged in two strong intermolecular H-bonding interactions forming a 3D supramolecular polymeric network. The geometry and vibrational frequencies of complex 1 computed with the DFT methods (BLYP, B3LYP, B3PW91, MPW1PW91) are in better agreement with experiment than those obtained with the ab-initio method except for the bond angles. The molecular orbital diagram has been also calculated and visualized at the B3LYP/LanL2DZ level of theory.      

Preparation and photovoltaic property of a new hybrid nanocrystalline SnO2/Polypyrrole p–n heterojunction

Hybrid photovoltaic structures based on transparent conductive SnO₂ and electrically conductive polypyrrole (PPy) were prepared. Nanocrystalline SnO₂ is considered an n-type barrier and window layer on p-type PPy layer in cell structures. The surface morphology and thickness of the layers were studied using scanning electron microscopy. The optical absorbance data showed an increase of absorbance in contrast with PPy and SnO₂. There was a red shift in absorbance wavelengths and a decrease in band gaps for the prepared PV structures. To investigate the electrical properties of the obtained structures, current-voltage characteristic was measured. The best structure showed an open-circuit voltage of 0.170?V, a short-circuit current density of 0.017?mA/cm², a fill factor of 0.36 and power conversion efficiency of 0.076.     

Off-lattice pattern recognition scheme for kinetic Monte Carlo simulations

We report the development of a pattern-recognition scheme for the off-lattice self-learning kinetic Monte Carlo (KMC) method, one that is simple and flexible enough that it can be applied to all types of surfaces. In this scheme, to uniquely identify the local environment and associated processes involving three-dimensional (3D) motion of an atom or atoms, space around a central atom is divided into 3D rectangular boxes. The dimensions and the number of 3D boxes are determined by the accuracy with which a process needs to be identified and a process is described as the central atom moving to a neighboring vacant box accompanied by the motion of any other atom or atoms in its surrounding boxes. As a test of this method to we apply it to examine the decay of 3D Cu islands on the Cu(100) and to the surface diffusion of a Cu monomer and a dimer on Cu(111) and compare the results and computational efficiency to those available in the literature.     

Metallization of the β-SiC(100) 3 × 2 surface: A DFT investigation

Using density functional theory (DFT) we report results for the electronic structure and vibrational dynamics of hydrogenated silicon carbide (001) (3 × 2) surfaces with various levels of hydrogenation. These results were obtained using density functional theory with a generalized gradient exchange correlation function. The calculations reveal that metallization can be achieved via hydrogen atoms occupying the second silicon layer. Further increase of hydrogen occupation on the second silicon layer sites results in a loss of this metallization. For the former scenario, where metallization occurs, we found a new vibrational mode at 1870 cm^? 1, which is distinct from the mode associated with hydrogen atoms on the first layer. Furthermore, we found the diffusion barrier for a hydrogen atom to move from the second to the third silicon layer to be 258 meV.     

A review on silicene — New candidate for electronics

Silicene-the silicon-based counterpart of graphene-has a two dimensional structure that is responsible for the variety of potentially useful chemical and physical properties. The existence of silicene has been achieved recently owing to experiments involving epitaxial growth of silicon as stripes on Ag(001), ribbons on Ag(110), and sheets on Ag(111). The nano-ribbons observed on Ag(110) were found-by both high definition experimental scanning tunneling microscopy images and density functional theory calculations-to consist of an arched honeycomb structure. Angle resolved photo-emission experiments on these silicene nano-ribbons on Ag(110), along the direction of the ribbons, showed a band structure which is analogous to the Dirac cones of graphene. Unlike silicon surfaces, which are highly reactive to oxygen, the silicene nano-ribbons were found to be resistant to oxygen reactivity.On the theoretical side, recent extensive efforts have been deployed to understand the properties of standalone silicene sheets and nano-ribbons using both tight-binding and density functional theory calculations. Unlike graphene it is demonstrated that silicene sheets are stable only if a small buckling (0.44 Å) is present. The electronic properties of silicene nano-ribbons and silicene sheets were found to resemble those of graphene.Although this is a fairly new avenue, the already obtained outcome from these important first steps in understanding silicene showed promising features that could give a new future to silicon in the electronics industry, thus opening a promising route toward wide-range applications. In this review, we plan to introduce silicene by presenting the available experimental and theoretical studies performed to date, and suggest future directions to be explored to make the synthesis of silicene a viable one.     

Electron–Phonon Superconductivity in Boron-Based Chalcogenide (X= S,Se) Monolayers

Electron–phonon mediated superconductivity is deeply investigated in two boron based monolayer materials, namely, $B_{3}S$, a metal exhibiting the ability to superconduct, and a new metal, $B_{3}Se$, presenting perfect kinetic stability. Calculations based on density functional perturbation theory combined with the maximally localized Wannier function also reveal that both materials exhibit anisotropic planar hexagonal structure like graphene. The key parameters involved in the superconductor behavior are all calculated. The electronic density in the Fermi surface is given to provide the environment for enhanced electron–phonon coupling. The longitudinal and transverse vibration modes of optical phonons mainly contribute to the electron–phonon coupling strength. Furthermore, the binding energy between the bosonic Cooper pair superfluid is quantified and determined. The critical temperature for the two materials is 20 and 10.5 K, respectively. The results obtained show the potential use of such materials for superconducting applications.