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41.
Pavlo Solokha Riccardo Freccero Serena De Negri Davide M. Proserpio Adriana Saccone 《Structural chemistry》2016,27(6):1693-1701
Direct synthesis and structural characterization of a series of polar rare earth palladium germanides of R2Pd3Ge5 composition (R = La–Nd, Sm) is reported. The crystal structure of the Nd representative was determined by single-crystal X-ray diffraction analysis (U2Co3Si5-type, SG: Ibam, oI40, Z = 4, a = 10.1410(6), b = 12.0542(8), c = 6.1318(4) Å, wR 2 = 0.0306, 669 F 2 values, 31 variables). The crystal structures of the other homologues were ensured by powder X-ray diffraction pattern analysis. A smooth variation of the cell dimensions is observed through the rare earth series. The structure of the studied compounds can be interpreted as consisting of a complex three-dimensional [Pd3Ge5]δ? network spaced by the rare earth cations. Within the concept of symmetry reduction, a Bärnighausen tree is used to rationalize the related crystal structures of the RPd2Ge2, RPdGe3 and R2Pd3Ge5 ternary compounds, enriching the large family of the BaAl4 derivatives. Moreover, syntheses with metal fluxes were performed, some of which were successful to obtain large crystals of La2Pd3Ge5 (using Bi as solvent) and Nd2Pd3Ge5 (using Pb as solvent) stoichiometry. 相似文献
42.
Gerhard König Frank C. Pickard IV Jing Huang Andrew C. Simmonett Florentina Tofoleanu Juyong Lee Pavlo O. Dral Samarjeet Prasad Michael Jones Yihan Shao Walter Thiel Bernard R. Brooks 《Journal of computer-aided molecular design》2016,30(11):989-1006
One of the central aspects of biomolecular recognition is the hydrophobic effect, which is experimentally evaluated by measuring the distribution coefficients of compounds between polar and apolar phases. We use our predictions of the distribution coefficients between water and cyclohexane from the SAMPL5 challenge to estimate the hydrophobicity of different explicit solvent simulation techniques. Based on molecular dynamics trajectories with the CHARMM General Force Field, we compare pure molecular mechanics (MM) with quantum-mechanical (QM) calculations based on QM/MM schemes that treat the solvent at the MM level. We perform QM/MM with both density functional theory (BLYP) and semi-empirical methods (OM1, OM2, OM3, PM3). The calculations also serve to test the sensitivity of partition coefficients to solute polarizability as well as the interplay of the quantum-mechanical region with the fixed-charge molecular mechanics environment. Our results indicate that QM/MM with both BLYP and OM2 outperforms pure MM. However, this observation is limited to a subset of cases where convergence of the free energy can be achieved. 相似文献
43.
Ivo F. Teixeira Benedict T. W. Lo Pavlo Kostetskyy Dr. Michail Stamatakis Dr. Lin Ye Prof. Chiu C. Tang Prof. Giannis Mpourmpakis Prof. Shik Chi Edman Tsang 《Angewandte Chemie (International ed. in English)》2016,55(42):13061-13066
We report a novel catalytic conversion of biomass‐derived furans and alcohols to aromatics over zeolite catalysts. Aromatics are formed via Diels–Alder cycloaddition with ethylene, which is produced in situ from ethanol dehydration. The use of liquid ethanol instead of gaseous ethylene, as the source of dienophile in this one‐pot synthesis, makes the aromatics production much simpler and renewable, circumventing the use of ethylene at high pressure. More importantly, both our experiments and theoretical studies demonstrate that the use of ethanol instead of ethylene, results in significantly higher rates and higher selectivity to aromatics, due to lower activation barriers over the solid acid sites. Synchrotron‐diffraction experiments and proton‐affinity calculations clearly suggest that a preferred protonation of ethanol over the furan is a key step facilitating the Diels–Alder and dehydration reactions in the acid sites of the zeolite. 相似文献
44.
Christian Gerhards Sergiy PereverzyevJr. Pavlo Tkachenko 《Advances in Computational Mathematics》2017,43(1):101-112
In many geoscientific applications, multiple noisy observations of different origin need to be combined to improve the reconstruction of a common underlying quantity. This naturally leads to multi-parameter models for which adequate strategies are required to choose a set of ‘good’ parameters. In this study, we present a fairly general method for choosing such a set of parameters, provided that discrete direct, but maybe noisy, measurements of the underlying quantity are included in the observation data, and the inner product of the reconstruction space can be accurately estimated by the inner product of the discretization space. Then the proposed parameter choice method gives an accuracy that only by an absolute constant multiplier differs from the noise level and the accuracy of the best approximant in the reconstruction and in the discretization spaces. 相似文献
45.
Domasevitch KV Solntsev PV Gural'skiy IA Krautscheid H Rusanov EB Chernega AN Howard JA 《Dalton transactions (Cambridge, England : 2003)》2007,(35):3893-3905
Nitrogen donor tetradentate ligands 4,4'-bipyridazine (bpdz) and pyridazino[4,5-d]pyridazine (pp) were prepared by inverse electron demand Diels-Alder cycloaddition reactions of 1,2,4,5-tetrazine. Examination of their behaviour towards silver(i) ions revealed a special potential of the ligands for the design of 3D coordination frameworks involving characteristic polynuclear and polymeric silver(i)-pyridazine motifs and multiple coordination of the ligands. Ag(4)(pp)(5)(ClO(4))(4) and Ag(4)(pp)(5)(SiF(6))(BF(4))(2).4H(2)O adopt a unique 3D trinodal 4,4,5-connected topology based upon five-fold coordination of the metal ions and tetradentate bridging function of the organic modules. Complexes Ag(3)(L)(3)(SO(3)CF(3))(3).nH(2)O and Ag(4)(L)(3)(X)(4).nH(2)O (L = bpdz, pp; X = BF(4)(-), 0.5SiF(6)(2-)) illustrate formation of highly-connected frameworks incorporating trinuclear clusters as an origin of the net connectivity. In the carboxylate complexes Ag(2)(L)(R(F)COO)(2) (R(F) = CF(3), C(2)F(5), C(3)F(7)) the pyridazine and acido ligands act as complementary linkers for generation of 3D frameworks involving helicate motifs. Fused bicyclic pyridazine pp is a unique system combining very efficient sigma(N)-donor ability and pronounced pi-acidity. The coordination frameworks commonly exhibit strong anion-pi interactions, including unprecedented examples of double anion-pi,pi binding that occur between pyridazino[4,5-d]pyridazine as a double pi,pi-receptor for geometry complementary SiF(6)(2-) anions. 相似文献
46.
Domasevitch KV Gural'skiy IA Solntsev PV Rusanov EB Krautscheid H Howard JA Chernega AN 《Dalton transactions (Cambridge, England : 2003)》2007,(29):3140-3148
A new polydentate ligand 4,4'-bipyridazine (4,4'-bpdz) was prepared by employing inverse electron demand cycloaddition of 1,2,4,5-tetrazine. A unique combination of structural simplicity, ampolydentate character and efficient donor properties towards Cu(I), Cu(II) and Zn(II) provide wide new possibilities for the synthesis of coordination polymers incorporating the 4,4'-bpdz module either as a bi-, tri- or tetradentate connector between the metal ions. 1D coordination polymers Cu(2)(4,4'-bpdz)(CH(3)CO(2))(4) x 4H(2)O and Zn(4,4'-bpdz)(NO(3))(2), and interpenetrated (4,4)-nets in [Cu(4,4'-bpdz)(2)(H(2)O)(2)]S(2)O(6) were closely related to 4,4'-bipyridine compounds. 1D "ladder-like" polymer Cu(2)(4,4'-bpdz)(3)(CF(3)CO(2))(4) and the unprecedented 3D binodal net ({8(6)}{6(3);8(3)}) in [Cu(3)(4,4'-bpdz)(6)(H(2)O)(4)](BF(4))(6) x 6H(2)O were based upon a combination of linear and angular organic bridges. Complex [Cu(3)(OH)(2)(4,4'-bpdz)(3)(H(2)O)(2){CF(3)CO(2)}(2)](CF(3)CO(2))(2) x 2H(2)O has a "NbO-like" 3D topology incorporating discrete dihydroxotricopper(II) clusters linked by tri- and tetradentate ligands. The tetradentate function of the 4,4'-bpdz ligand was especially relevant for copper(I) complexes, which adopt layered Cu(2)X(2)(4,4'-bpdz) (X = Cl, Br) or 3D chiral framework (X = I) structures based upon infinite (CuX)(n) chains. The electron deficient character of the ligand was manifested by short anion-pi interactions (O-pi 3.02-3.20; Cl-pi 3.35 A), which may be involved as a factor for controlling the supramolecular structure. 相似文献
47.
A Fluorescent Molecular Probe for the Detection of Hydrogen Based on Oxidative Addition Reactions with Crabtree‐Type Hydrogenation Catalysts
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M. Sc. Pavlo Kos Prof. Dr. Herbert Plenio 《Angewandte Chemie (International ed. in English)》2015,54(45):13293-13296
A Crabtree‐type IrI complex tagged with a fluorescent dye (bodipy) was synthesized. The oxidative addition of H2 converts the weakly fluorescent IrI complex (Φ=0.038) into a highly fluorescent IrIII species (Φ=0.51). This fluorogenic reaction can be utilized for the detection of H2 and to probe the oxidative addition step in the catalytic hydrogenation of olefins. 相似文献
48.
Dr. Marko Förstel Dr. Pavlo Maksyutenko Dr. Brant M. Jones Dr. Bing‐Jian Sun Dr. Shih‐Hua Chen Prof. Dr. Agnes. H.‐H. Chang Prof. Dr. Ralf I. Kaiser 《Chemphyschem》2015,16(15):3139-3142
We report the detection of triazane (N3H5) in the gas phase. Triazane is a higher order nitrogen hydride of ammonia (NH3) and hydrazine (N2H4) of fundamental importance for the understanding of the stability of single‐bonded chains of nitrogen atoms and a potential key intermediate in hydrogen–nitrogen chemistry. The experimental results along with electronic‐structure calculations reveal that triazane presents a stable molecule with a nitrogen–nitrogen bond length that is a few picometers shorter than that of hydrazine and has a lifetime exceeding 6±2 μs at a sublimation temperature of 170 K. Triazane was synthesized through irradiation of ammonia ice with energetic electrons and was detected in the gas phase upon sublimation of the ice through soft vacuum ultraviolet (VUV) photoionization coupled with a reflectron‐time‐of‐flight mass spectrometer. Isotopic substitution experiments exploiting [D3]‐ammonia ice confirmed the identification through the detection of its fully deuterated counterpart [D5]‐triazane (N3D5). 相似文献
49.
The influence of electron attachment on the stability of the mono- and dihydrogenated buckminsterfullerene C(60) was studied using density functional theory and semiempirical molecular orbital techniques. We have also assessed the reliability of computationally accessible methods that are important for investigating the reactivity of graphenic species and surfaces in general. The B3LYP and M06L functionals with the 6-311+G(d,p) basis set and MNDO/c are found to be the best methods for describing the electron affinities of C(60) and C(60)H(2) . It is shown that simple frontier molecular orbital analyses at both the AM1 and B3LYP/6-31G(d) levels are useful for predicting the most favourable position of protonation of C(60)H(-) , that is, formation of the kinetically controlled product 1,9-dihydro[60]fullerene, which is also the thermodynamically controlled product, in agreement with experimental and previous theoretical studies. We have shown that reduction of exo- and endo-C(60)H makes them more stable in contrast to the reduction of the exo,exo-1,9-C(60)H(2) , reduced forms of which decompose more readily, in agreement with experimental electrochemical studies. However, most other dihydro[60]fullerenes are stabilized by reduction and the regioselectivity of addition is predicted to decrease as the less stable isomers are stabilized more by the addition of electrons than the two most stable ones (1,9 and 1,7). 相似文献
50.
We carried out the crossed molecular beam reaction of ground state methylidyne radicals, CH(X(2)Π), with acetylene, C(2)H(2)(X(1)Σ(g)(+)), at a nominal collision energy of 16.8 kJ mol(-1). Under single collision conditions, we identified both the atomic and molecular hydrogen loss pathways forming C(3)H(2) and C(3)H isomers, respectively. A detailed analysis of the experimental data suggested the formation of c-C(3)H(2) (31.5 ± 5.0%), HCCCH/H(2)CCC (59.5 ± 5.0%), and l-HCCC (9.0 ± 2.0%). The reaction proceeded indirectly via complex formation and involved the unimolecular decomposition of long-lived propargyl radicals to form l-HCCC plus molecular hydrogen and HCCCH/H(2)CCC plus atomic hydrogen. The formation of c-C(3)H(2) was suggested to be produced via unimolecular decomposition of the cyclopropenyl radical, which in turn could be accessed via addition of the methylidyne radical to both carbon atoms of the acetylene molecule or after an initial addition to only one acetylenic carbon atom via ring closure. This investigation brings us closer to unraveling of the reaction of important combustion radicals-methylidyne-and the connected unimolecular decomposition of chemically activated propargyl radicals. This also links to the formation of C(3)H and C(3)H(2) in combustion flames and in the interstellar medium. 相似文献