Hydrogen Complexes Research Articles

DFT calculations on the cyclic ethers hydrogen-bonded complexes: Molecular parameters and the non-linearity of the hydrogen bond

B3LYP/6-311+G(d,p) calculations were used to explore the geometry, intermolecular energy and the vibrational harmonic spectrum of heterocyclic complexes formed between 2,5-dihydrofuran and thiophene cyclic ethers and the HCl and HF acids. The simulated structures of these hydrogen complexes are discussed in terms of the linearity deviation of the n⋯HX hydrogen bond. Theoretical results are satisfactory as compared to the experimental equilibrium structure. The energies of the hydrogen bonds were determinate through the difference between the complex and its correspondent isolated monomers. Moreover, to obtain the correct energies of the hydrogen bonds, it was included the values of the zero point vibrational energy and the basis set superposition error. The infrared spectra reveal the direct relationship between the distance of the hydrogen bond and its stretching frequencies, as well as a good interpretation of the bathochromic effect of the HCl and HF stretching modes from intermolecular charge transfer.

Snapshots of the “breaking” of the H-H bond in the oxidative addition of H2 to a metal centre

Three new monocationic molecular hydrogen complexes of ruthenium of the typetrans-[RuCl(η2-H2)(PP)2][BF4] (PP = bis-l,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, benzyl,p-methyl-benzyl) have been prepared by protonating the precursor hydride complexes trans-[RuCl(H)(PP)2] using HBF4.Et20. These three dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H-H bond in these derivatives has been established from the short spin-lattice relaxation times(T 1, ms) and the observation of substantial H, D couplings in the HD isotopomers. The H-H bond distances(d HH, å) increase from 0.97 to 1.01 å as the electron donor ability of the diphosphine ligand increases from the p-fluorobenzyl to the benzyl to the p-methylbenzyl moiety. These dihydrogen complexes constitute the initial stages of elongation of the H-H bond enroute to its cleavage along the reaction coordinate for the oxidative addition of H2 to a metal centre.

Thermochromic and photochromic behaviour of “chameleon” diamonds

Chameleon diamonds typically change color from greyish-green to yellow when they are heated or cooled (thermochromic behaviour) or kept in the dark (photochromic behaviour). Those diamonds are type Ia with A aggregates largely dominating the nitrogen speciation. They contain moderate to high amounts of hydrogen, in addition to some isolated nitrogen and traces of nickel. Their UV Visible spectrum comprises the continuum typical of type Ib material, the 480 nm band and a broad band centred around 800 nm. It is mainly modified in the red part of the visible spectrum when the color change occurs. We here propose an electronic model consistent with all observed color behaviours, based on the premise that yellow is the stable color whereas green is the metastable one. The chameleon effect is possibly linked to a nitrogen–hydrogen complex.

Polarimetry in the Outskirts of NGC 6611

Fil: Orsatti, Ana Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Astrofisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronomicas y Geofisicas. Instituto de Astrofisica la Plata; Argentina

The hydrogen bond in the acetylene-2(HF) complex: A theoretical study about intramolecular and unusual π⋯H interactions using DFT and AIM calculations

We present a theoretical study about hydrogen complexes formed by acetylene and hydrofluoric acid using B3LYP/6-311++G(d,p) calculations and topological parameters of the atoms in molecules theory. In the C 2H 2 2(HF) hydrogen bonded complex, besides the well-known (π⋯H) interaction formed between the hydrofluoric acid and the C C bond of the acetylene, as well as the (F d⋯H e) hydrogen bond in the 2(HF) dimer within the ternary hydrogen complex, the topological parameters identified a bond critical point proceeding from interaction between the fluoride atom (F f) of the second HF molecule and the hydrogen atom (H b) of the acetylene, characterizing then a new hydrogen bond, (F f⋯H b). Moreover, the AIM calculations discovered an important aspect relative to the (π⋯H) interaction, which is not linked in the midpoint of the C C bond of the acetylene but formed directly by the interaction between the hydrogen atom (H c) of the first HF molecule and the C 2 atom of the acetylene in the C 2H 2 2(HF) complex. In this sense, the C 2H 2 2(HF) hydrogen bonded complex can be considered an intramolecular system constituted of three hydrogen bonds.

Hydrogen bonds in alcohols:water complexes: A theoretical study about new intramolecular interactions via CHELPG and AIM calculations

The structures of the alcohols:water hydrogen complexes were fully optimized using B3LYP/ccp-VDZ calculations. We apply a set of criteria developed in terms of the CHELPG atomic charges and topological parameters of the atoms in molecules theory to evaluate the proton donor–acceptor behavior of the water molecule within the both ethanol:water and t-butanol:water complexes. The results show that the water molecule interacts simultaneously with the hydroxyl and the hydrogen atoms of the methyl groups in the ethanol and t-butanol, respectively.

The hydrogen bond strength: New proposals to evaluate the intermolecular interaction using DFT calculations and the AIM theory

The optimized geometries of the H 2O–H 2O, H 2O–HF, H 2O–HCN, NH 3–HF, HF–HF, NH 3–HCN, H 2O–NH 3 and HCN–HCN hydrogen complexes were evaluated using B3LYP/6-311++G(d, p) calculations and parameters derived from Bader’s atoms in molecules theory. Moreover, in accordance with the relation existent between the hydrogen bond energy and the increments in the bond length of the proton donor species, we present new proposals to estimate the hydrogen bond strength through the atoms in molecules calculations, as well as using traditional parameters such as atomic charge transfer and the infrared bathochromic effect of the acid molecules.

Theory of hydrogen complexes in Mn xGa1-xAs dilute magnetic semiconductors

Atomic hydrogen diffuses in semiconductor lattices and binds to impurities by forming complexes that can lead to a full neutralization of the impurity effects. In the present paper, the structural, vibrational, electronic and magnetic properties of complexes formed by H in the Mn xGa1-xAs (x=0.03) dilute magnetic semiconductor have been investigated by using first-principles DFT-LSD and LDA+U theoretical methods. The results account for recent experimental findings showing a H passivation of the electronic and magnetic properties of Mn in GaAs. Moreover, they show that electron correlation has crucial effects on the properties of H-Mn complexes.

Reduction of Multiple Bonds without Hydrogen or Hydride Complexes: Samarium Diiodide as a Mild Reducing Reagent

AbstractThe use of samarium diiodide as a mild and selective reducing agent has become an important tool in organic synthesis. Many reducing agents are reported in the literature. However, due to their low chemoselectivities and various other drawbacks, samarium diiodide has become a useful and readily available reagent. This manuscript provides an update on earlier reviews describing conventional reduction processes of multiple bonds promoted by samarium diiodide. The most recent developments in the use of samarium metal in this field are also discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Hydrogen-induced transient effect in carbon-doped InGaP hetero-junction bipolar transistors

The transient effect on the current gain of InGaP hetero-junction bipolar transistors was studied. It was found that this transient effect was caused by hydrogen and eliminated after three or more cycles of thermal annealing at 250°C in nitrogen. A model based on the carbon–hydrogen complex dissociation by thermal anneal is proposed to explain this observation.

Ab-initio modeling of acceptor–hydrogen complexes in CdTe

We have investigated the hydrogenation of group-V impurities ( N Te , P Te and As Te ) in CdTe by computer modeling, using a pseudopotential density-functional method. For these complexes, we found that the lowest energy location for hydrogen is near the bond-center, closer to the acceptor atom, between a Cd atom and the acceptor. Metastable states by 0.5 eV above the ground state where found for structures where H is anti-bonding to N Te , P Te and As Te . The calculated local vibrational mode (LVM) frequencies for the bond centered configurations agree within 3% of the experimental values, i.e. 3210 cm - 1 for N Te –H and 2022 cm - 1 for As Te –H. Deuterium LVM induced shifts for As Te –D fall within 4% of the experimental data. The observed wag mode for N Te –H is reproduced within 8%. A wag mode for As Te –H and LVM frequencies for P Te –H are predicted.

Potential energy surface and infrared spectra of OCS–hydrogen complexes

We present a full-dimensional potential energy surface for the OCS–H2 system that includes explicit dependence on the Q 3 normal vibration of the OCS molecule. From the integration of this potential over the Q 3 coordinate two vibrationally adiabatic surfaces are generated. These are then used to compute the rovibrational energies for the OCS–H2 complexes with the OCS molecule in both its ground and first excited vibrational states and for all H2 isotopomers. Comparison with the available experimental data shows an overall good agreement for all spectroscopic parameters. The full potential energy surface is also integrated over the H2 angular variables to obtain a reduced dimensionality effective potential that describes the interaction between an OCS molecule and a spherical H2 molecule. The accuracy of this approximation, widely employed in Monte Carlo simulations of H2 clusters, is then analysed here in the case of the OCS–H2 complexes by comparing the rovibrational energies computed with the present potential interaction in both full and reduced dimensionality.

A theoretical study of ethylene dehydrogenation by bare Niobium atom and cation

The potential energy profiles corresponding to the dehydrogenation reaction of C 2H 4 by bare Nb atom and cation have been investigated employing the Density Functional Theory in its B3LYP formulation. All the minima and key transition states have been examined along both high- and low-spin pathways. The reaction proceeds toward dehydrogenation products by formation of a stable donor–acceptor complex, oxidative addition of the metal into one of the H–C bonds to give a hydrido-complex and, finally, formation of a molecular hydrogen complex that releases hydrogen without an energy barrier. Since the spin of the ground state reactants is different from that of adduct formed at the entrance channel, spin multiplicity has to change along the lowest energy reaction path involving transition states that lie always below the ground state reactants asymptote.

Ab Initio Analysis on Stability of Carbon-Hydrogen Complex in Si Crystal under Compressive Stress along [110] Direction

We have analysed the stability of carbon (C)-hydrogen (H) complex in compressively stressed silicon (Si) single crystal with ab initio calculation. First, the relationship between tensile stress and the strain of Si crystal along [100], [110] or [111] direction was obtained. It was found that the calculated Young's modules of Si crystal agreed with experimental results within 10% difference. Next, the stable structure of C-H complex in strain-free Si crystal was investigated with calculating the total energy of several structures. It was found that the most stable structure consists of the substitutional C atom and interstitial H atom located at the nearest bond center (B) site. Binding energy of C and H atom was about 1.25 eV. Finally, we have studied the stability of C-H complex under uniaxial [110] compressive stress. Here, [110] direction is in (110) Si plane and perpendicular to (110) Si plane. Total energies were compared between complex A (C-H complex is in (110) plane) and complex B (C-H complex is in (110) plane). It was found that complex B is more stable than A from 0.25 to 15 GPa compressive stress.

A theoretical study of hydrogen complexes of the X [sbnd]H-π type between propyne and HF, HCL or HCN

The present manuscript reports a systematic investigation of the basis set dependence of some properties of hydrogen-bonded (π type) complexes formed by propyne and a HX molecule, where X = F, Cl and CN. The calculations have been performed at Hartree–Fock, MP2 and B3LYP levels. Geometries, H-bond energies and vibrational have been considered. The more pronounced effects on the structural parameters of the isolated molecules, as a result of complexation, are verified on R C C and HX bond lengths. As compared to double-ζ (6-31G **), triple-ζ (6-311G **) basis set leads to an increase of R C C bond distance, at all three computational levels. In the case where diffuse functions are added to both hydrogen and ‘heavy’ atoms, the effect is more pronounced. The propyne–HX structural parameters are quite similar to the corresponding parameters of acetylene–HX complexes, at all levels. The largest difference is obtained for hydrogen bond distance, R H, with a smaller value for propyne–HX complex, indicating a stronger bond. Concerning the electronic properties, the results yield the following ordering for H-bond energies, Δ E: propyne⋯HF > propyne⋯HCl > propyne⋯HCN. It is also important to point out that the inclusion of BSSE and zero-point energies (ZPE) corrections cause significant changes on Δ E. The smaller effect of ZPE is obtained for propyne⋯HCN at HF/6-311++G ** level, while the greatest difference is obtained at MP2/6-31G ** level for propyne⋯HF system. Concerning the IR vibrational it was obtained that larger shift can be associated with stronger hydrogen bonds. The more pronounced effect on the normal modes of the isolated molecule after the complexation is obtained for H X stretching frequency, which is shifted downward.

Open‐Cage Fullerenes: Synthesis, Structure, and Molecular Encapsulation

AbstractFor Abstract see ChemInform Abstract in Full Text.

Production of sodium borohydride by using dynamic behaviors of protide at the extreme surface of magnesium particles

An advanced process for the production of sodium borohydride (NaBH 4) as a hydrogen storage material was developed, which applied the dynamic hydriding and dehydriding behaviors of protide (H −) in Mg–H system under transitional temperature conditions. An abundant natural resource named borax (Na 2B 4O 7⋅10H 2O) and the anhydrous sodium metaborate (NaBO 2) recovered from the “spent fuel” as NaBO 2⋅4H 2O were used as the starting material in the present process. Powder-state Mg played an important role in the transitional hydriding and dehydriding process where the gaseous hydrogen was converted to protide at the extreme surface of Mg to form NaBH 4 in exchange with the simultaneous transition of oxygen in NaBO 2 to form MgO. In the present process, the protide as the most reactive state among the four states of hydrogen is applied for the synthesis of NaBH 4, which can exist in metal–hydrogen complexes, such as NaAlH 4 and NaBH 4. The NaBH 4 yield was reached higher than 90% by a single batch process but was found to be largely dependent on the rate of temperature change and the particle size, i.e., the specific surface area of Mg particles.

Formation of hydrogen complexes in proton implanted silicon and their influence on the crystal damage

We studied the rearrangement of ion-implanted hydrogen in 〈100〉 oriented n-type silicon wafers upon annealing and its effect on the crystal damage. The obtained results reveal information about the damage accumulation caused by the thermally induced rearrangement of the implanted Hydrogen. The gained knowledge was correlated to the depth distributions and orientations of H-platelets, which formed during annealing and were examined by cross-section transmission electron microscopy analysis.

Electronic transport properties ofPd‐Hjunctions between twoPdHx(x=0,0.25,0.5,0.75,1)electrodes: A nonequilibrium Green’s function study

Using a fully self-consistent nonequilibrium Green's function method combined with the density functional theory, the transport properties of $\mathrm{Pd}\ensuremath{-}\mathrm{H}$ junctions between two $\mathrm{Pd}{\mathrm{H}}_{x}$ $(x=0,0.25,0.5,0.75,1)$ electrodes are investigated systematically. Three different hydrogen bridges are considered, including a single hydrogen atom configuration, a hydrogen molecule configuration with the $\mathrm{H}\mathrm{H}$ bond axis parallel to the transport direction and a complex ${\mathrm{Pd}}_{2}{\mathrm{H}}_{2}$ configuration where the ${\mathrm{H}}_{2}$ molecule dissociates. For the pure Pd nanojunction, the transmission spectrum drops sharply near the Fermi level and gives an average conductance of about $1.8{G}_{0}$. Four channels are found to have significant contributions to the conductance. The electronic structures of the electrodes are modified by the doping of H in the bulk. The presence of hydrogen between and in two electrodes changes the transmission spectra obviously, while the number of the eigenchannels of the junction is only determined by the electronic structure of the neck region. For the pure Pd electrodes, the calculated conductances of three kinds of hydrogen bridges are about 1.1, 0.5, and $0.9\phantom{\rule{0.3em}{0ex}}{G}_{0}$, respectively. For the heavy doping of H in the Pd electrodes, the conductances of hydrogen bridges with a hydrogen molecule or complex ${\mathrm{Pd}}_{2}{\mathrm{H}}_{2}$ configurations range from 0.3 to $0.7\phantom{\rule{0.3em}{0ex}}{G}_{0}$. The calculated results agree very well with the experimental values.

Structure and stability ofO−Hdonors in ZnO from high-pressure and infrared spectroscopy

Zinc oxide (ZnO) is a wide-band-gap semiconductor with potential optical, electronic, and mechanical applications. First-principles investigations [C. G. Van de Walle, Phys. Rev. Lett. 85, 1012 (2000)] predicted that hydrogen impurities act as shallow donors in ZnO. IR spectroscopy [M. D. McCluskey et al., Appl. Phys. Lett. 81, 3807 (2002)] showed that a local vibrational mode at $3326.3\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, at liquid-helium temperatures, corresponded to an $\mathrm{O}\ensuremath{-}\mathrm{H}$ type bond. The microscopic structure of this hydrogen complex, however, was not determined. In this Brief Report, the structure and stability of $\mathrm{O}\ensuremath{-}\mathrm{H}$ complexes are discussed. The second excited state of the $\mathrm{O}\ensuremath{-}\mathrm{H}$ stretch mode was found at $6389\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, allowing us to compare the experimental results with the harmonic calculations of Van de Walle. Results from high-pressure and polarized IR spectroscopy strongly suggest that hydrogen occupies an antibonding location with an $\mathrm{O}\ensuremath{-}\mathrm{H}$ bond oriented at an angle of 111\ifmmode^\circ\else\textdegree\fi{} to the $c$ axis. By correlating the IR absorbance strength with free-electron concentration, it was established that the $\mathrm{O}\ensuremath{-}\mathrm{H}$ complexes are shallow donors. However, the $\mathrm{O}\ensuremath{-}\mathrm{H}$ donors are unstable, decaying significantly after several weeks at room temperature. The kinetics of the dissociation follow a bimolecular decay model, consistent with the formation of ${\mathrm{H}}_{2}$ molecules.