Potential curves for proton motion in H-bonded systems: HF and H2O polymers

The presence of long range coupling between hydrogen atoms is shown for the HF and H₂O hydrogen bonded systems. The coupling of H atoms critically depends on the spatial orientation of the H atoms being considered. Explicit calculations of the potential curves of the protons are performed using as a model a ring of six HF, or H₂O, molecules. The method of calculation is the CNDO/2. The strong similarities of the results for H₂O and HF polymers supports the conclusion that the coupling is essentially due to factors such as the asymmetric equilibrium position of the H atoms, the high electronic polarizability of the system, etc.     

Hydrogen fluoride vibrational energy distributions for the reactions of fluorine atoms with cyclanes

The hydrogen fluoride infrared chemiluminescence produced by the reactions of fluorine atoms with cyclopropane, cyclopentane, and cyclohexane have been studied. The emission data were used to determine the vibrational energy distributions for the abstraction of hydrogen from the secondary carbon–hydrogen bonds of these small cyclic hydrocarbons. The fraction of reaction exothermicity going into vibrational excitation of hydrogen fluoride was as follows: c-C₃H₆, 45%; c-C₅H₁₀, 53%; c-C₆H₁₂, 49%. The slightly lower fraction for the cyclopropane system may indicate that its radical reorganization energy is not completely available for excitation of product HF.     

Interplay between Metal⋅⋅⋅π Interactions and Hydrogen Bonds: Some Unusual Synergetic Effects of Coinage Metals and Substituents

The ternary systems of C₂H₄ (C₂H₂ or C₆H₆)‐MCN‐HF (M=Cu, Ag, Au) and the respective binary systems were investigated to study the interplay between metal???π interactions and hydrogen bonds. The metal???π interactions in C₂H₄‐MCN become stronger with the irregular order Ag<Cu<Au, while the hydrogen bonds in MCN‐HF become weaker following the same order. The metal???π interactions are weakened as the H atoms in the π system are replaced with electron‐withdrawing groups and enhanced by electron‐donating groups. Type 1 of these ternary systems, in which MCN acts as Lewis base and acid simultaneously, is more stable than type 2, in which C₂H₄ acts as a double Lewis base. Negative cooperativity is present in type 2 ternary systems with a weakening of the metal???π interactions and the hydrogen bonds. Positive cooperativity is found in type 1 ternary systems with an enhancement of the metal???π interactions and the hydrogen bonds, except for C₂(CN)₄‐AuCN‐HF‐1. The weaker metal???π interaction in C₆H₆‐AuCN has a greater enhancing effect on the hydrogen bond in AuCN‐HF than those in C₂H₄‐AuCN and C₂H₂‐AuCN. These synergetic effects were analyzed with the natural bond orbital and energy decomposition.     

Are the hydrogen bonds involving sulfur bases inverse or anomalous?

The hydrogen‐bonded complexes (HBCs) of H₂S, CH₂S, and CH₄S with H–F (hydrogen fluoride) were studied within the framework of the quantum theory of atoms in molecules at several theoretical levels (HF, B3LYP, MP2, and QCISD) with a wide range of basis sets. According to the integrated atomic populations obtained at correlated levels, the interacting hydrogen of the acid gains charge upon complexation, in sharp contrast to the conventional picture of hydrogen bonding, whereas the HF method yields a small loss of charge. The study of several H_nA…H_mD HBCs of hydrides, where A is the hydrogen‐acceptor atom and D is the atom bonded to the hydrogen donor, reveals this behavior is followed when the electronegativity of D significantly exceeds that of A. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Cooperativity between the Halogen Bond and the Hydrogen Bond in H3N⋅⋅⋅XY⋅⋅⋅HF Complexes (X,Y=F,Cl, Br)

Ab initio calculations are used to provide information on H₃N???XY???HF triads (X, Y=F, Cl, Br) each having a halogen bond and a hydrogen bond. The investigated triads include H₃N???Br₂‐HF, H₃N???Cl₂???HF, H₃N???BrCI???HF, H₃N???BrF???HF, and H₃N???ClF???HF. To understand the properties of the systems better, the corresponding dyads are also investigated. Molecular geometries, binding energies, and infrared spectra of monomers, dyads, and triads are studied at the MP2 level of theory with the 6‐311++G(d,p) basis set. Because the primary aim of this study is to examine cooperative effects, particular attention is given to parameters such as cooperative energies, many‐body interaction energies, and cooperativity factors. The cooperative energy ranges from ?1.45 to ?4.64 kcal mol^?1, the three‐body interaction energy from ?2.17 to ?6.71 kcal mol^?1, and the cooperativity factor from 1.27 to 4.35. These results indicate significant cooperativity between the halogen and hydrogen bonds in these complexes. This cooperativity is much greater than that between hydrogen bonds. The effect of a halogen bond on a hydrogen bond is more pronounced than that of a hydrogen bond on a halogen bond.     

Molecular orbital theory of the hydrogen bond.: XVI. A comparative study of pyridine and the diazines as proton acceptors in ground and excited n → π* states

Ab initio LCAO MO SCF calculations with a minimal STO-3G basis set have been performed to determine the structures and energies of dimers having pyridazine, pyrimidine, and pyrazine as proton acceptor molecules, with HF and H₂O as proton donors. The structures of these dimers are consistent with structures anticipated from the General Hybridization Model. Differences in the relative stabilities of dimers in the two series which have HF and H₂O as proton donors and pyridine and the diazines as proton acceptors are attributed to different weightings of secondary effects which influence dimer stabilities. These azabenzeme molecules form stronger hydrogen bonds than HCN and weaker hydrogen bonds than NH₃ whether HF or H₂O is the proton donor. Configuration interaction calculations indicate that vertical excitation to n → π* states of these proton aceptor molecules results in various degrees of destabilization of hydrogen bonded dimers and trimers, depending upon the excited state electron densities at the nitrogen atoms and the excited state dipole moments. With respect to the proton acceptor molecule, computed blue shifts of the n → π* bands increase in the order pyrazine < pyradizine < pyrimidine < pyridine.     

Fluoride und Fluorosäuren. V. Kristallstruktur der 1:4-Phase im System Wasser-Fluorwasserstoff und eine neue Untersuchung einer der 1:2-Phasen

Fluorides and Fluoro Acids. V. Crystal Structure of the 1:4 Phase in the System Water-Hydrogen Fluoride and a New Investigation of One of the 1:2 Phases In the quasi binary system H₂O? HF the 1:2 phase of known crystal structure was recognized as the stable high-temperature phase. A more accurate redetermination of its structure (monoclinic, space group P2₁/c, Z = 4, a = 3.477, b = 6.024, c = 11.358 Å, β = 96.70° at ?100°C, R = 0.032 for 1356 observed MoKα data) confirmed the previous results of a layer structure formed by strong hydrogen bonds. H₃OF · HF appears besides H₃OHF₂ as a possible structural formula. — The crystal structure of the 1:4 phase of the system was also determined (triclinic, P1 , Z = 2, a = 5.574, b = 6.429, c = 6.874 Å, α = 115.79, β = 96.63, γ = 108.79° at ?113°C, R = 0.049 for 1942 observed MoKα data). By strong hydrogen bonds the atoms form rings, which are condensed to parallel ribbons. Possible structural formulae, based on the distribution of interatomic distances, are H₃OH₃F₄, H₃OH₂F₃ · HF and H₃OF · 3 HF. — Interatomic distances in the hydrogen bonds F? H…?F and O? H…?F of both structures and the known one of the 1:1 phase are discussed in comparison.     

Rates of processes initiated by pulsed laser production of F atoms in the presence of HCl,CH4, and CF3H

Time-resolved vibrational chemiluminescence from HF has been recorded following the production of F atoms by the pulsed laser photolysis (λ = 266 nm) of F₂ in the presence of HCl, CH₄, and CF₃H. In the first two cases, experiments have been conducted by observing emission from HF(ν = 3) at four temperatures from 295 to 139 K. Rate constants have been determined over this range of temperature for the reactions of F atoms with HCl and CH₄ and of CH₃ radicals with F₂, and for the relaxation of HF(ν = 3) by HCl and CH₄. The reaction of F atoms with CF₃H is slower than those with HCl and CH₄ and measurements on the emission from HF(ν = 2) have been used to infer rate constants for reaction and relaxation only at 295 K. © 1994 John Wiley & Sons, Inc.     

Time resolved HF vibrational fluorescence from the IR photodissociation of SF6/H2 mixtures

Time resolved measurements of HF spontaneous emission, following the irradiation of SF₆/H₂ mixtures with the focused output from a CO₂ TEA laser, are reported. Our results indicate that F atoms are produced directly by the photodissociation process, and that these atoms have a recoil energy which is ≤500 cm^?1, and varies only slightly with the radiation intensity. Further, our results show a linear dependence of fluorescence intensity with laser energy, indicating that processes other than direct photodissociation may play a significant role in the ultimate fate of species excited by IR collisionless multiple photon absorption.     

High-capacity hydrogen storage of magnesium-decorated boron fullerene

By theoretical analysis, we have explored the feasibility of functionalizing boron fullerene (B₈₀) by adsorbing Mg atoms for the application as hydrogen storage nanomaterials. Our results show that due to the charge transfer from Mg to B atoms Mg atoms reside above the pentagonal faces of the B₈₀ cage. The electric field induced around the positive charged Mg atoms polarizes H₂ molecules, and the resulting binding is strong enough to adsorb H₂ without dissociation. Further calculations indicated that the 12Mg-decorated-B₈₀ has a high hydrogen storage capacity storing up to 96 H₂ molecules with an ideal binding energy of 0.20 eV/H₂ according to the approximation of GGA and 0.5 eV/H₂ according to LDA, corresponding to a hydrogen uptake of 14.2%. This suggested a possible method of engineering new structure for high-capacity hydrogen storage materials with the reversible adsorption and desorption of hydrogen molecules.     

Ab initio investigation of water clusters (H2O)n (n = 2–34)

Various properties of typical structures of water clusters in the n = 2–34 size regime with the change of cluster size have been systematically explored. Full optimizations are carried out for the structures presented in this article at the Hartree–Fock (HF) level using the 6‐31G(d) basis set by taking into account the positions of all atoms within the cluster. The influence of the HF level on the results has been reflected by the comparison between the binding energies of (H₂O)_n (n = 2–6, 8, 11, 13, 20) calculated at the HF level and those obtained from high‐level ab initio calculations at the second‐order Møller–Plesset (MP2) perturbation theory and the coupled cluster method including singles and doubles with perturbative triples (CCSD(T)) levels. HF is inaccurate when compared with MP2 and CCSD(T), but it is more practical and allows us to study larger systems. The computed properties characterizing water clusters (H₂O)_n (n = 2–34) include optimal structures, structural parameters, binding energies, hydrogen bonds, charge distributions, dipole moments, and so on. When the cluster size increases, trends of the above various properties have been presented to provide important reference for understanding and describing the nature of the hydrogen bond. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Correlated one‐electron wave functions

Using four basis sets, 6‐311G(d,p), 6‐31+G(d,p), 6‐311++G(2d,2p), and 6‐311++G(3df,3pd), the optimized structures with all real frequencies were obtained at the MP2 level for dimers CH₂O? HF, CH₂O? H₂O, CH₂O? NH₃, and CH₂O? CH₄. The structures of CH₂O? HF, CH₂O? H₂O, and CH₂O? NH₃ are cycle‐shaped, which result from the larger bend of σ‐type hydrogen bonds. The bend of σ‐type H‐bond O…H? Y (Y?F, O, N) is illustrated and interpreted by an attractive interaction of a chemically intuitive π‐type hydrogen bond. The π‐type hydrogen bond is the interaction between one of the acidic H atoms of CH₂O and lone pair(s) on the F atom in HF, the O atom in H₂O, or the N atom in NH₃. By contrast with above the three dimers, for CH₂O? CH₄, because there is not a π‐type hydrogen‐bond to bend its linear hydrogen bond, the structure of CH₂O? CH₄ is a noncyclic shaped. The interaction energy of hydrogen bonds and the π‐type H‐bond are calculated and discussed at the CCSD(T)/6‐311++G(3df,3pd) level. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Long‐range π‐type hydrogen bond in dimers CH2?HF,CH2O?H2O,and CH2O?NH3

Using four basis bets, (6‐311G(d,p), 6‐31+G(d,p), 6‐31++G(2d,2p), and 6‐311++G(3df,3pd), the optimized structures with all real frequencies were obtained at the MP2 level for the dimers CH₂O? HF, CH₂O? H₂O, CH₂O? NH₃, and CH₂O? CH₄. The structures of CH₂O? HF, CH₂O? H₂O, and CH₂O? NH₃ are cycle‐shaped, which result from the larger bend of σ‐type hydrogen bonds. The bend of σ‐type H‐bond O…H? Y (Y?F, O, N) is illustrated and interpreted by an attractive interaction of a chemically intuitive π‐type hydrogen bond. The π‐type hydrogen bond is the interaction between one of the H atoms of CH₂O and lone pair(s) on the F atom in HF, the O atom in H₂O, or the N atom in NH₃. In contrast with the above three dimers, for CH₂O? CH₄, because there is not a π‐type hydrogen bond to bend its linear hydrogen bond, the structure of CH₂O? CH₄ is noncyclic shaped. The interaction energy of hydrogen bonds and the π‐type H‐bond are calculated and discussed at the CCSD (T)/6‐311++G(3df,3pd) level. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Where gold meets a hydrogen bond?

This is a short survey of the area of the hydrogen bonding where the noble and coinage metal gold enters its manifold of the proton acceptors. It is largely focused on the nonconventional hydrogen bonds that are formed in the complexes of the auride anion Au⁻ with HF, (HF)₂, H₂O, (H₂O)₂, NH₃, and (NH₃)₂, as mostly experimentally investigated to date. A thorough comparison of the experimental and computational data on these nonconventional hydrogen bonds is the main motif of the present work.     

Can BB double bond be as potential proton acceptor: A UB3LYP and UMP2 theoretical study on unusual intermolecular T-shaped XH…π interactions between the triplet state HBBH and HF, HCl, HCN or H2C2

The unusual weak T-shaped XH…π hydrogen bonds are found between the BB double bond of the triplet state HBBH and the acid hydrogen of HF, HCl, HCN and H₂C₂ using UMP2 and UB3LYP methods at 6-311++G(2df,2p) and aug-cc-pVTZ levels. The binding energies follow the order of HBBH…HF > HBBH…HCl > HBBH…HCN > HBBH…H₂C₂, and the hydrogen-bonded interactions in the triplet state complexes HBBH…HX (³B₁) are found to be weaker than those in HCCH…HX and OCBBCO…HX. The analyses of natural bond orbital (NBO) and the electron density shifts reveal that the nature of the T-shaped XH…π hydrogen-bonded interaction is that the lost density from the π-orbital of BB bond is shifted toward the hydrogen atom of HX, leading to the electron density accumulation and the formation of the hydrogen bond. The atoms in molecules (AIM) theory has been also applied to characterize bond critical points and confirm that it is difficult for the ground electronic state of HBBH to be as the hydrogen-bond proton acceptor, perhaps due to the nature of electron-deficient BB double bond.     

Superconducting Phases of Phosphorus Hydride Under Pressure: Stabilization by Mobile Molecular Hydrogen

At 80 GPa, phases with the PH₂ stoichiometry, which are composed of simple cubic like phosphorus layers capped with hydrogen atoms and layers of H₂ molecules, are predicted to be important species contributing to the recently observed superconductivity in compressed phosphine. The electron–phonon coupling in these phases results from the motions of the phosphorus atoms and the hydrogen atoms bound to them. The role of the mobile H₂ layers is to decrease the Coulomb repulsion between the negatively charged hydrogen atoms capping the phosphorus layers. An insulating PH₅ phase, the structure and bonding of which is reminiscent of diborane, is also predicted to be metastable at this pressure.     

Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide,Formaldehyde, and Sodium Hydroxide

In 1923, Wieland and Wingler reported that in the molecular hydrogen producing reaction of hydrogen peroxide with formaldehyde in basic solution, free hydrogen atoms (H^.) are not involved. They postulated that bis(hydroxymethyl)peroxide, HOCH₂OOCH₂OH, is the intermediate, which decomposes to yield H₂ and formate, proposing a mechanism that would nowadays be considered as a “concerted process”. Since then, several other (conflicting) “mechanisms” have been suggested. Our NMR and Raman spectroscopic and kinetic studies, particularly the determination of the deuterium kinetic isotope effect (DKIE), now confirm that in this base‐dependent reaction, both H atoms of H₂ derive from the CH₂ hydrogen atoms of formaldehyde, and not from the OH groups of HOCH₂OOCH₂OH or from water. Quantum‐chemical CBS‐QB3 and W1BD computations show that H₂ release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH₂OOCH₂OH, thereby ruling out a free radical pathway.     

Interactions of metal‐encapsulated fullerenes with solvents

The present investigation reports on the interaction of M@C₆₀(M = Be, Mg, Ca) with solvents (H₂O, CH₃OH, HF, NH₃) using Density Functional Theory calculations. Our computations reveal that the interaction of the fullerene species increases when endohedral metal atoms are inserted into its cavity. The most profound interaction of the fullerene systems is with water and hydrogen fluoride. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Gaseous products of the bombardment of a tetrafluoroethylene–hexafluoropropylene copolymer with accelerated MeV protons

The action of 1- to 4-MeV protons on a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) in a vacuum is accompanied by the release of more than 25 gaseous products and a decrease in its thermal stability. During the course of proton bombardment, the predominant rupture of lateral C–CF₃ bonds with the release of CF₃ particles occurs along with the detachment of fluorine and hydrogen atoms yielding H₂ and HF. Unlike polytetrafluoroethylene, a distinctive feature of the radiolysis of FEP is a decrease by a factor of 5 in the probability of fluorine detachment from the FEP macromolecule by accelerated protons.