The interaction of fluorosilanes with hydrogen fluoride clusters: strongly blue-shifted hydrogen bonds

The equilibrium structures, binding energies, and vibrational spectra of the complexes formed between hydrogen fluoride clusters (HF)_n (1≤n≤4) and the fluorosilanes SiHF₃, SiH₂F₂, and SiH₃F are investigated within the second-order Møller–Plesset perturbation theory method applying extended basis sets. It is shown that Si–FH–F halogen–hydrogen bonds are formed in the most stable open dimers, SiHF₃–HF, SiH₂F₂HF, and SiH₃FHF. No Si–HF–H hydrogen bonds occur in these dimers. Nevertheless, blue shifts of Si–H stretching frequencies are calculated. All three trimers, fluorosilane–(HF)₂, all three tetramers, fluorosilane–(HF)₃, and two of the pentamers, fluorosilane–(HF)₄, form cyclic structures with strong Si–FH–F halogen–hydrogen bonds and weak Si–HF–H contacts, the latter displaying, nevertheless, strongly blue-shifted Si–H stretching frequencies. These blue shifts are comparable in size to those of the corresponding fluoromethane–(HF)_n complexes and are with about +50 cm⁻¹ for the case n=3 among the largest ever calculated and definitely the largest for Si–H bonds. In the title complexes, the formation of the Si–FH–F halogen–hydrogen bonds induces a substantial stretching of this Si–F bond, which in turn leads to a significant contraction of the fluorosilane Si–H bond in the Si–HF–H hydrogen bond. This disposition of the fluorosilane monomers is demonstrated with the aid of suitable potential energy surface scans and appears to be a prerequisite for the formation of strongly blue-shifted hydrogen bonds.     

Blue-shifted A-H stretching modes and cooperative hydrogen bonding. 1. Complexes of substituted formaldehyde with cyclic hydrogen fluoride and water clusters

The structures and vibrational spectra of the intermolecular complexes formed by insertion of substituted formaldehyde molecules HRCO (R = H, Li, F, Cl) into cyclic hydrogen fluoride and water clusters are studied at the MP2/aug-cc-pVTZ computational level. Depending on the nature of the substituent R, the cluster type, and its size, the C-H stretching modes of HRCO undergo large blue and partly red shifts, whereas all the F-H and O-H stretching modes of the conventional hydrogen bonds are strongly red-shifted. It is shown that (i) the mechanism of blue shifting can be explained within the concept of the negative intramolecular coupling between C-H and C=O bonds that is inherent to the HRCO monomers, (ii) the blue shifts also occur even if no hydrogen bond is formed, and (iii) variation of the acceptor X or the strength of the C-H...X hydrogen bond may either amplify the blue shift or cause a transition from blue shift to red shift. These findings are illustrated by means of intra- and intermolecular scans of the potential energy surfaces. The performance of the negative intramolecular coupling between C-H and C=O bonds of H(2)CO is interpreted in terms of the NBO analysis of the isolated H(2)CO molecule and H(2)CO interacting with (H2O)n and (HF)n clusters.     

Nonconventional hydrogen bonding between clusters of gold and hydrogen fluoride

The bonding patterns between small neutral gold Au(3 < or = n < or = 7) and hydrogen fluoride (HF)(1 < or = m < or = 4) clusters are discussed using a high-level density functional approach. Two types of interactions, anchoring Au-F and F-H...Au, govern the complexation of these clusters. The F-H...Au interaction exhibits all the characteristics of nonconventional hydrogen bonding and plays a leading role in stabilizing the lowest-energy complexes. The anchor bonding mainly activates the conventional F-H...F hydrogen bonds within HF clusters and reinforces the nonconventional F-H...Au one. The strength of the F-H...Au bonding, formed between the terminal conventional proton donor group FH and an unanchored gold atom, depends on the coordination of the involved gold atom: the less it is coordinated, the stronger its nonconventional proton acceptor ability. The strongest F-H...Au bond is formed between a HF dimer and the singly coordinated gold atom of a T-shape Au4 cluster and is accompanied by a very large red shift (1023 cm(-1)) of the nu(F-H) stretch. Estimations of the energies of formation of the F-H...Au bonds for the entire series of the studied complexes are provided.     

Electron and hydrogen transfer in small hydrogen fluoride anion clusters

A new stable structure has been found for the anion clusters of hydrogen fluoride. The ab initio method was used to optimize the structures of the (HF)(3)(-), (HF)(4)(-), (HF)(5)(-), and (HF)(6)(-) anion clusters with an excess "solvated" electron. Instead of the well-known "zig-zag" (HF)(n)(-) structure, a new form, (HF)(n-1)F(-)···H, was found with lower energy. In this new form, the terminal hydrogen atom in the (HF)(n)(-) chain is separated from the other part of the cluster and the inner hydrogens transfer along the hydrogen bonds toward the outside fluoride. The negative charge also transfers from the terminal HF molecule of the chain to the center fluoride atoms. The (HF)(n)(-) clusters for n = 4, 5, and 6 have not yet been observed experimentally. These results should assist in the search for these systems and also provide a possible way to study the proton and electron transfer in some large hydrogen bonding systems.     

Overtone spectroscopy of C-H ethyl stretches of 1-butyne

Room-temperature photoacoustic (PA) spectra and jet-cooled action spectra of the first to third overtone regions of the ethyl C-H stretches in vapor phase 1-butyne, CH3CH2C[Triple Bond]C-H, were measured. Both the PA and action spectra exhibit a complex multiple peak structure being better resolved and more pronounced in the latter, due to inhomogeneous structure reduction. The observed manifolds were analyzed in terms of a simplified joint local-/normal-mode (LM/NM) model accounting for two types of C-H stretches (methyl and methylene) and for Fermi resonances between stretches and deformations. The retrieved parameters, used for calculation of the eigenstates, come from the best-fit parameters based on the diagonalization of the vibrational Hamiltonian in the LM/NM basis. The parameters were obtained by comparing the eigenvalues and the sum of the squares of the expansion coefficients of the eigenvectors of the C-H stretches of methyl and methylene to the action spectra peak positions and intensities, respectively. This approximate model vibrational Hamiltonian is proposed to explain most observed spectral features, corresponding to C-H stretch bands and to combinations of C-H stretches and deformations, indicating the importance of the Fermi resonance. The model was also applied to calculate the dynamics of the C-H stretching modes resulting from coupling with the deformations, implying rapid initial state decay on subpicosecond time scale. Decays of several picoseconds were found for complete transfer of probability from the initially prepared state of methylene and methyl to the counterpart LM states.     

On the physical origin of blue-shifted hydrogen bonds

For blue-shifted hydrogen-bonded systems, the hydrogen stretching frequency increases rather than decreases on complexation. In computations at various levels of theory, the blue-shift in the archetypical system, F(3)C-H.FH, is reproduced at the Hartree-Fock level, indicating that electron correlation is not the primary cause. Calculations also demonstrate that a blue-shift does not require either a carbon center or the absence of a lone pair on the proton donor, because F(3)Si-H.OH(2), F(2)NH.FH, F(2)PH.NH(3), and F(2)PH.OH(2) have substantial blue-shifts. Orbital interactions are shown to lengthen the X-H bond and lower its vibrational frequency, and thus cannot be the source of the blue-shift. In the F(3)CH.FH system, the charge redistribution in F(3)CH can be reproduced very well by replacing the FH with a simple dipole, which suggests that the interactions are predominantly electrostatic. When modeled with a point charge for the proton acceptor, attractive electrostatic interactions elongate the F(3)C-H, while repulsive interactions shorten it. At the equilibrium geometry of a hydrogen-bonded complex, the electrostatic attraction between the dipole moments of the proton donor and proton acceptor must be balanced by the Pauli repulsion between the two fragments. In the absence of orbital interactions that cause bond elongation, this repulsive interaction leads to compression of the X-H bond and a blue-shift in its vibrational frequency.     

Anion-arene adducts: C-H hydrogen bonding, anion-pi interaction, and carbon bonding motifs

This article summarizes experimental and theoretical evidence for the existence of four distinct binding modes for complexes of anions with charge-neutral arenes. These include C-H hydrogen bonding and three motifs involving the arene-pi system-the noncovalent anion-pi interaction, weakly covalent sigma interaction, and strongly covalent sigma interaction.     

Determining the vibrational pattern via overtone cold spectra: C-H methyl stretches of propyne

Vibrationally mediated photodissociation and photoacoustic (PA) spectroscopy were employed for studying the intramolecular dynamics of propyne initially excited to the first through fourth overtone of methyl C-H stretching modes. Room-temperature PA and jet-cooled action spectra, monitoring the absorption of the parent and the yield of the ensuing H photofragments, respectively, were obtained. The PA spectra exhibit mainly broad features, while the action spectra, due to inhomogeneous structure reduction, expose multiple peaks of recognizable shapes in the differing overtone manifolds. Symmetric rotor simulations of the band contours of the action spectra allowed retrieving of band origins and linewidths. The linewidths of the bands in each manifold enabled estimates for energy redistribution times out of the corresponding states to the bath states, the times ranging from 18+/-6 ps for two quanta of C-H excitation to subpicosecond for five quanta. The data were also analyzed in terms of a normal-mode model and a joint local-/normal-mode model. These models enabled determination of harmonic frequencies, anharmonicities, and interaction parameters reproducing the observed data in all monitored regions and provided spectral assignments. The measured Doppler profiles were well fitted by Gaussians with widths suggesting low average translational energies for the released H photofragments. These low energies and their similarities to those for dissociation of propyne isotopomers preexcited to acetylenic C-H stretches were ascribed to an indirect dissociation process occurring after internal conversion to the ground electronic state and isomerization to allene.     

Reaction of formaldehyde with hydrogen sulfide

Conclusions The reaction of CH₂O with H₂S gives a complex mixture of mercapto derivatives; the conversion of the latter to polymethylene sulfide is accomplished in the presence of a basic catalyst.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1631–1633, July, 1982.     

Potential energy surfaces for the interaction of hydrogen atoms with beryllium metal clusters

With a modified CNDO/2 molecular orbital approach, potential energy surfaces are computed for the attack of beryllium atom clusters simulating “smooth” (0001) and “corrugated” (1010) faces of beryllium metal. Several stable sites for chemisorption are found with binding energies of 40–55 kcal/mole, but penetration of the lattice appears possible at some points. Results are compared with the preliminary ab initio predictions of Bauschlicher, Liskow, Bender and Schaefer.     

Nature of hydrogen interaction and saturation on small titanium clusters

This work explores the nature of interaction and saturation of hydrogen molecules on small titanium clusters using ab initio calculations. Molecular dynamics simulations and ensuing charge density maps were used to gain insight into the key steps involved in dissociation of the hydrogen molecule on the metal clusters. The mechanistic insights gleaned from these simulations were subsequently utilized to obtain realistic models of the hydrogen saturated titanium clusters. It was found that the most stable hydrogen saturated titanium clusters involve hydrogen multicenter bonds. The observed peaks in the experimental mass and photoelectron spectra of hydrogen saturated titanium clusters are attributed to structures possessing hydrogen multicenter bonds. Hydrogen multicenter bonds are also ascribed to the origin of the broad shoulder in the vibrational spectra of hydrogen cycled Ti-doped NaAlH4 reported in a recent study.     

Quantum-chemical investigation on hydrogen bonding interaction of hydrogen fluoride dimer at various mutual orientations

Hydrogen bonding interaction in hydrogen fluoride dimer has been investigated by quantum-chemical calculation with 6-311G^** basis set at various mutual orientations. Atomic charges and charge transfer have been calculated by means of potential-derived method, and decomposition of hydrogen bonding interaction has been executed. The calculation results show that there is a variation range for the energy-stable orientations, the charge transfer in the range presents maximum value, and the charge transfer interaction plays a decisive role in the hydrogen bonding.     

Potential energy surfaces for the interaction of atomic and diatomic hydrogen with lithium metal clusters

In this paper a modified CNDO/2 method is used to study the interaction of hydrogen atoms and molecules with molecular clusters simulating the (100) surface of solid lithium metal. The modification, described in an earlier papers, involves rescaling bicentric CNDO/2 energy contributions with known diatomic bond energies. Potential energy curves are calculated for six attack points by the hydrogen atom on the surface, and for one attack point by the molecule. The results indicate that in both atom and molecule forms hydrogen penetrates the surface and that the molecule most likely dissociates.     

Reactions of aminophenols with formaldehyde and hydrogen sulfide

The reaction of m-aminophenol with CH₂O and H₂S (1: 2: 1 ratio) afforded 2, 12-dioxa-4, 14-dithia-6, 16-diazatricyclo[15.3.1.1^7,11]docosa-1(20), 7(22), 8, 10, 17(21), 18-hexaene in ∼9% yield. Aminophenol o-and p-isomers react with CH₂O and H₂S (1: 3: 2) to form 2-and 4-[4H-1,3,5-dithiazin-5(6H)-yl]phenols in 86 and 71% yields, respectively. In the crystal structure of the latter, molecules contain dithiazine cycles in the chair conformation with the axial hydroxyphenyl group. Molecular packing represents a combination of molecules forming chains due to the OH...S intermolecular hydrogen bond. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 305–308, February, 2006.     

Reaction dynamics and vibrational spectroscopy of CH3D molecules with both C-H and C-D stretches excited

State-resolved reactions of CH3D molecules containing both C-H and C-D stretching excitation with Cl atoms provide new vibrational spectroscopy and probe the consumption and disposal of vibrational energy in the reactions. The vibrational action spectra have three different components, the combination of the C-H symmetric stretch and the C-D stretch (nu1 + nu2), the combination of the C-D stretch and the C-H antisymmetric stretch (nu2 + nu4), and the combination of the C-D stretch and the first overtone of the CH3 bend (nu2 + 2nu5). The simulation for the previously unanalyzed (nu2 + nu4) state yields a band center of nu0 = 5215.3 cm(-1), rotational constants of A = 5.223 cm(-1) and B = 3.803 cm(-1), and a Coriolis coupling constant of zeta = 0.084. The reaction dynamics largely follow a spectator picture in which the surviving bond retains its initial vibrational excitation. In at least 80% of the reactive encounters of vibrationally excited CH3D with Cl, cleavage of the C-H bond produces CH2D radicals with an excited C-D stretch, and cleavage of the C-D bond produces CH3 radicals with an excited C-H stretch. Deviations from the spectator picture seem to reflect mixing in the initially prepared eigenstates and, possibly, collisional coupling during the reaction.     

Interaction of hydrogen fluoride with ruthenium tetroxide

In the course of the studies concerning hydrolysis of ruthenium fluorides and fluorination of ruthenium hydroxides, we frequently noticed the formation of a volatile substance which showed a strong absorption band at 1030 cm^?1. We pursued this unknown substance and found that it was an adduct between ruthenium tetroxide and hydrogen fluoride:

This new adduct, RuO₄(HF)₁₀, is observable at temperature higher than 0°C and at HF pressure greater than 150 mmHg. Between 4000 and 200 cm^?1, the adduct shows two absorption bands—1030 cm^?1 and 389 cm^?1. At 0°C, the adduct in the gas-phase disappears for condensation.On the basis of these results, credibility of the earlier literature on RuF₈ was discussed.     

Model study of the nonadiabatic effects in the interaction of atomic hydrogen with lithium metal clusters

Study is made of the effects of adsorption site position on mutual arrangement and nonadiabatic coupling between the lowest two singlet potential energy surfaces of the Li₉(4, 1, 4)-H chemisorption system. Special attention is paid to a normal approach of H atom to Li₉ cluster. The necessary energy and coupling data are obtained by use of the method of the diatomics-in-molecules. The changes with the alteration of the adsorption site position of the degree of nonadiabatic behaviour of system is shown to be quite significant.     

SCF LCGO MO studies on the fluoronium ion FH 2 + and its hydrogen bonding interaction with hydrogen fluoride FH

The stability and geometrical structure of the fluoronium ion is investigated using the onedeterminant SCF LCAO MO method. The equilibrium geometry is characterized by a bond length of d(FH)=0.95 Å and a bond angle of 114.75°. The proton binding energy is determined to be 120.1 kcal/mole. The molecules FH ₃ ²⁺ and FH₃ are found to be unstable. A binding energy of 30.7 kcal/mole is obtained for the hydrogen bond formation between the systems FH ₂ ⁺ and FH. In the minimum energy structure the central proton is situated midway between the two F atoms in a symmetrical single minimum potential. The general behavior of the potential curves of the di-solvated proton involving NH₃, OH₂, and FH as solvent molecules is discussed. In all these cases double minimum potentials are found, if the equilibrium separation between the heavy atoms is larger than approximately 2.4 Å, and single minimum potential for separations smaller than this value.     

Theoretical study of the N-H…O red-shifted and blue-shifted hydrogen bonds

Theoretical calculations are performed to study the nature of the hydrogen bonds in complexes HCHO…HNO, HCOOH…HNO, HCHO…NH3, HCOOH…NH3, HCHO…NH2F and HCOOH…NH2F. The geometric structures and vibrational frequencies of these six complexes at the MP2/6-31+G(d,p), MP2/6-311++G(d,p), B3LYP/6-31+G(d,p) and B3LYP/6-311++G(d,p) levels are calculated by standard and counterpoise-corrected methods, respectively. The results indicate that in complexes HCHO…HNO and HCOOH…HNO the N-H bond is strongly contracted and N-H…O blue-shifted hydrogen bonds are observed. While in complexes HCHO…NH3, HCOOH…NH3, HCHO…NH2F and HCOOH…NH2F, the N-H bond is elongated and N-H…O red-shifted hydrogen bonds are found. From the natural bond orbital analysis it can be seen that the X-H bond length in the X-H…Y hydrogen bond is controlled by a balance of four main factors in the opposite directions: hyperconjugation, electron density redistribution, rehybridization and structural reorganization. Among them hyperconjugation has the effect of elongating the X-H bond, and the other three factors belong to the bond shortening effects. In complexes HCHO…HNO and HCOOH…HNO, the shortening effects dominate which lead to the blue shift of the N-H stretching frequencies. In complexes HCHO…NH3, HCOOH…NH3, HCHO…NH2F and HCOOH…NH2F where elongating effects are dominant, the N-H…O hydrogen bonds are red-shifted.