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Calculations Support (calculation + support)
Selected AbstractsSodium Hydro(isothiocyanato)borates: Synthesis and StructuresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2004Heinrich Nöth Abstract Sodium thiocyanate reacts in THF solution with 18-crown-6 to give the molecular compound Na(18-crown-6)(THF)NCS (3) with the N atom of the NCS anion oriented towards Na+. The same reaction with 15-crown-5 yields the ion pair Na(15-crown-5)NCS (4). In contrast, Na(NCS)(py)4, obtained by treating a solution of Na(H3BNCS) in THF with pyridine, yields Na(py)4(NCS) (5), which has a chain structure with hexacoordinate Na atoms coordinated to five N atoms and an S atom. Na(NCS) in THF adds 1 equiv. of BH3 to give Na(H3BNCS)·nTHF. Addition of 18-crown-6 to this solution yields crystals of the salt [Na(18-crown-6)(THF)2][H3BNCS] (1), as shown by X-ray crystallography. Both the cation and the anion show site disorder. However, when 15-crown-5 is used for complexation, the salt [Na(15-crown-5)(THF)][H3BNCS] (2) can be isolated. Its anion shows an almost linear B,N,C,S unit. Only a mixture of (catecholato)(isothiocyanato)borates results on treating Na(NCS) in THF with catecholborane. However, the borate Na[catB(NCS)2] is readily formed by adding Na(NCS) to B -(isothiocyanato)catecholborane. Single crystals of this compound were obtained as the salt [Na(18-crown-6)(THF)2][catB(NCS)2] (6). On the other hand, the reaction of Na(NCS) with 9-borabicyclo[3.3.1]nonane (9-BBN) in THF yields Na[(9-BBN)NCS)]·nTHF, and, on addition of 18-crown-6, the complex [Na(18-crown-6)(THF)2][(9-BBN)NCS] was isolated. Suitable crystals for X-ray structure determination were, however, only obtained by crystallization from tetrahydropyran. This solvate has the rather unusual structure [Na(18-crown-6)(thp)2][{(9-BBN)NCS}2Na(thp)4] (8). The sodiate anion has an Na atom coordinated by two S and four O atoms. DFT calculations support these experimental results: The (isothiocyanato)borates are more stable than the thiocyanato isomers. For the latter a bent structure of the B,S,C,N unit with a B,S,C bond angle of 105.7° is predicted. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Intercalates of Vanadyl Phosphate with Benzonitrile and TolunitrileEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2003Ludvík Bene Abstract Intercalates of vanadyl phosphate with benzonitrile and p -tolunitrile were prepared and characterized by X-ray powder diffraction, TG analysis, IR and Raman spectroscopy. Both intercalates contain one nitrile molecule per formula unit. The intercalates prepared are moisture sensitive and guest molecules are easily replaced by water molecules. The nitrile molecules are anchored to the host layers by an N,V donor-acceptor bond. Local structures and interactions appearing in the intercalates were suggested on the base of quantum chemical calculations. These calculations support the results of the IR and Raman spectroscopy, indicating the formation of a C,N,V bond in the intercalates. The calculated basal spacings (11.32 Å for the benzonitrile and 13.00 Å for the tolunitrile intercalates) are in good agreement with the experimental values (11.22 and 13.19 Å, respectively). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Deslipping of Ester Rotaxanes: A Cooperative Interplay of Hydrogen Bonding with Rotational BarriersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2003Petra Linnartz Abstract A series of rotaxanes has been synthesized which contain two ester groups in their axles. All rotaxanes bear the same tetralactam wheel. The kinetics of the de-slipping reaction of these rotaxanes were monitored in tetrachloroethane (TCE) and dimethyl sulfoxide (DMSO) resulting in the observation of a significant solvent effect. In TCE, two isomeric rotaxanes that differ merely with respect to the orientation of the ester groups show a remarkable difference in their deslipping behavior. When the ester carbonyl group is directly attached to the axle center piece, the rotaxane decomposes with a half life of ca. 10 h at 100 °C. The reverse orientation with the carbonyl group attached to the stopper blocks deslipping almost completely and a lower limit for the half life at 100 °C of 25,000 h was obtained. These results can be interpreted by inferring a cooperative action of hydrogen bonding between wheel and axle and differences in rotational barriers. Molecular modeling and AM1 calculations support this interpretation. The implications of these results for the determination of steric size and the optimization of molecular machines are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] The First General and Selective Palladium(II)-Catalyzed Alkoxycarbonylation of Arylboronates: Interplay among Benzoquinone-Ligated Palladium(0) Complex, Organoboron, and Alcohol SolventADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Yoshihiko Yamamoto Abstract Methoxycarbonylation of aryl- and alkenylboron compounds was performed using the palladium(II) acetate/triphenylphosphine [Pd(OAc)2/PPh3] catalyst with p -benzoquinone as a stoichiometric oxidant in methanol at ambient temperature to obtain the corresponding methyl esters in good yields. A wide variety of functional groups including various carbonyl functionalities, nitrile, nitro, sulfone, and unprotected pyrrole rings were tolerated in the methoxycarbonlation, while the use of higher alcohols except for tert -butanol afforded various p -chlorobenzoates in moderate to high yields. The catalytic alkoxycarbonylation proceeded without any acid or base additive, and an oxidative transmetalation step is proposed to explain the exceptional efficacy of this protocol. DFT and MP2 calculations support the proposed mechanism. [source] A petrologic study of the IAB iron meteorites: Constraints on the formation of the IAB-Winonaite parent bodyMETEORITICS & PLANETARY SCIENCE, Issue 6 2000G. K. BENEDIX These meteorites contain inclusions that fall broadly into five types: (1) sulfide-rich, composed primarily of troilite and containing abundant embedded silicates; (2) nonchondritic, silicate-rich, comprised of basaltic, troctolitic, and peridotitic mineralogies; (3) angular, chondritic silicate-rich, the most common type, with approximately chondritic mineralogy and most closely resembling the winonaites in composition and texture; (4) rounded, often graphite-rich assemblages that sometimes contain silicates; and (5) phosphate-bearing inclusions with phosphates generally found in contact with the metallic host. Similarities in mineralogy and mineral and O-isotopic compositions suggest that IAB iron and winonaite meteorites are from the same parent body. We propose a hypothesis for the origin of IAB iron meteorites that combines some aspects of previous formation models for these meteorites. We suggest that the precursor parent body was chondritic, although unlike any known chondrite group. Metamorphism, partial melting, and incomplete differentiation (i.e., incomplete separation of melt from residue) produced metallic, sulfide-rich and silicate partial melts (portions of which may have crystallized prior to the mixing event), as well as metamorphosed chondritic materials and residues. Catastrophic impact breakup and reassembly of the debris while near the peak temperature mixed materials from various depths into the re-accreted parent body. Thus, molten metal from depth was mixed with near-surface silicate rock, resulting in the formation of silicate-rich IAB iron and winonaite meteorites. Results of smoothed particle hydrodynamic model calculations support the feasibility of such a mixing mechanism. Not all of the metal melt bodies were mixed with silicate materials during this impact and reaccretion event, and these are now represented by silicate-free IAB iron meteorites. Ages of silicate inclusions and winonaites of 4.40-4.54 Ga indicate this entire process occurred early in solar system history. [source] Blue-shift of absorption edge in LaTiO2N by controlling the anion nonstoichiometryPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006Toshihiro Moriga Abstract The perovskite-type oxynitride LaTiO2N was prepared by heating an oxide precursor at 950 °C for 5 hours under NH3 atmosphere at a flow rate of 1 dm3/min. The precursor was prepared by the polymerized complex method. The oxynitride obtained was almost stoichiometric, LaTi(O0.68N0.32)2.9, with a reddish orange color. The oxynitride was successively annealed at 950 °C for 3 hours under a NH3 atmosphere at flow rates of 50 cm3/min, 30 cm3/min and 10 cm3/min, respectively. The color and composition varied from yellow LaTi(O0.89N0.11)2.8 through green-yellow LaTi(O0.93N0.07)2.9 to light-blue LaTi(O0.98N0.02)2.9 in accordance with the decreased flow rate. The absorption edges varied from 2.28 eV for the reddish orange, 2.56 eV for the yellow, 3.17 eV for the green-yellow, to 3.44 eV for the light-blue oxynitrides. Annealing under NH3 is therefore effective in color tuning, mainly resulting in a blue-shift of the absorption edge. DV-X, calculations support the conclusion that the lower flow rate of NH3 led to a lower amount of nitrogen and higher oxygen levels in the oxynitrides. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Evidence for Spontaneous Release of Acrylates from a Transition-Metal Complex Upon Coupling Ethene or Propene with a Carboxylic Moiety or CO2CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2007Michele Aresta Prof. Abstract The development of a new synthetic approach to acrylates based on the formation of alkyl esters of acrylic acids has been studied. A preformed Pd,COOMe moiety is used as a model system to investigate the insertion of an olefin into the PdC bond. The fast elimination of acrylate is observed. Density functional calculations support the experimental findings and allow the characterization of transition states along the reaction pathway. The first example of olefin/CO2 coupling with facile release of ethyl acrylate is also presented. [source] Photosensitization and the Photocurrent Switching Effect in Nanocrystalline Titanium Dioxide Functionalized with Iron(II) Complexes: A Comparative StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2007Wojciech Macyk Dr. Abstract Selected iron(II) complexes (ferrocene, ferrocenylboronic acid, hexacyanoferrate(II)) have been used as photosensitizers of titanium dioxide. Various types of electronic interactions between the surface complex and the semiconducting support are reflected in different yields of photocurrent generated upon visible-light irradiation and different efficiencies of the photosensitization effect. The studied systems, showing the photocurrent switching upon changes of electrode potential and energy of photons (the PEPS effect), are good models of simple photoelectrochemical logic devices. The mechanism of photosensitization and photocurrent switching is discussed with respect to the type of surface-complex,support interaction. Quantum-mechanical calculations support the proposed mechanisms. Wybrane kompleksy ,elaza(II) (ferrocen, kwas ferrocenyloboronowy i heksacyjano,elazian(II)) zosta,y u,yte jako fotosensybilizatory dwutlenku tytanu. Ró,ne typy oddzia,ywa, elektronowych pomi,dzy kompleksami powierzchniowymi a pod,o,em pó,przewodnikowym znajduj, odbicie w ró,nych wydajno,ciach generacji fotopr,du i ró,nym stopniu fotosensybilizacji materia,ów na ,wiat,o widzialne. Wszystkie badane uk,ady wykazuj, efekt fotoelektrochemicznego prze,,czenia fotopr,du na skutek zmian potencja,u fotoelektrody i zmian d,ugo,ci fali ,wiat,a padaj,cego (efekt PEPS), dlatego te, stanowi, bardzo dobre modele prostych prze,,czników fotoelektrochemicznych. Niniejsza praca szczegó,owo okre,la mechanizm fotosensybilizacji i prze,,czenia fotopr,du na podstawie analizy oddzia,ywa, pomi,dzy kompleksem a powierzchni, pó,przewodnika. Obliczenia kwantowo-mechaniczne potwierdzaj, postulowany mechanizm. [source] Fullerene-like Mo(W)1,xRexS2 NanoparticlesCHEMISTRY - AN ASIAN JOURNAL, Issue 8-9 2008Francis, Leonard Deepak Dr. Abstract Inorganic fullerene-like (IF) Mo1,xRexS2 and W1,xRexS2 nanoparticles have been synthesized by a gas-phase reaction involving the respective metal halides with H2S. The IF-Mo(W)1,xRexS2 nanoparticles, containing up to 5,% Re, were characterized by a variety of experimental techniques. Analyses of the X-ray powder diffraction and different electron microscopy techniques show that the Re is doped in the MoS2 host lattice. Interestingly, Re-doped MoS2 nanotubes are present as well, although in small quantities (,5,%). XPS results confirm the nanoparticles to be more n-type arising from the effect of Re doping. Additionally, density-functional tight-binding (DFTB) calculations support the observed n-type behavior. [source] | |||||||||||||||||||||||||