On differences between hydrogen bonding and improper blue-shifting hydrogen bonding.

Twenty two hydrogen-bonded and improper blue-shifting hydrogen-bonded complexes were studied by means of the HF, MP2 and B3LYP methods using the 6-31G(d,p) and 6--311 ++G(d,p) basis sets. In contrast to the standard H bonding, the origin of the improper blue-shifting H bonding is still not fully understood. Contrary to a frequently presented idea, the electric field of the proton acceptor cannot solely explain the different behavior of the H-bonded and improper blue-shifting H-bonded complexes. Compression of the hydrogen bond due to different attractive forces-dispersion or electrostatics--makes an important contribution as well. The symmetry-adapted perturbation theory (SAPT) has been utilized to decompose the total interaction energy into physically meaningful contributions. In the red-shifting complexes, the induction energy is mostly larger than the dispersion energy while, in the case of blue-shifting complexes, the situation is opposite. Dispersion as an attractive force increases the blue shift in the blue-shifting complexes as it compresses the H bond and, therefore, it increases the Pauli repulsion. On the other hand, dispersion in the red-shifting complexes increases their red shift.     

Studies in hydrogen bonding: Association within small clusters of water,methanol, and ammonia molecules using Jorgensen's intermolecular pair potentials

The geometries of the dimer, trimer, and tetramer hydrogen-bonded clusters of water, methanol, and ammonia molecules have been derived using previously published intermolecular pair potentials containing constants optimized from ab initio calculations. The lowest energy forms for the dimers of all three types of molecules have an open structure, while the trimers and tetramers have cyclic structures. The results are compared with those previously described using another empirical potential, EPEN .     

Structure and property of the hydrogen bonding complex between triazines and water

The study of the intermolecular interactions that drive the solvation of six-membered nitrogenated aromatic rings is of particular importance since they are known to constitute key building blocks of pro- teins and nucleotides[1―5]. The investigation of the 1:1 adduct of these molecules with water will be the first step in the understanding of such interactions. These molecules possess two different proton-acceptor sites: the ring π cloud and the lone pairs of electrons on the nitrogen atoms…     

Influence of hydrogen bonding on the properties of water molecules adsorbed in zeolite frameworks

Three hydrated aluminosilicate frameworks—LiABW, NaNAT, and BaEDI—are partly optimized with the periodic Hartree–Fock CRYSTAL95 code. In particular, we optimized the positions of the adsorbed water molecules including the positions of the framework cations (ABW, NAT) or part of the framework atomic positions (ABW). This allowed us to compare cation–water clusters in the gas and adsorbed states and discuss the influence of hydrogen bonding to the framework oxygen atoms or to the neighbor water molecules on the atomic properties (quadrupole coupling constant, anisotropy of electric field gradient) of the adsorbed water molecules. The LiBIK structure obtained from X‐ray diffraction is also considered to illustrate the hydrogen bonds occurring between adsorbed water molecules. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

On the relationship between the preferred site of hydrogen bonding and protonation

Ab initio molecular orbital calculations have been employed to investigate the interactions between a set of basic substrates (B) with H+ and HF, and the interaction between acids of varying strength (AH+) with two bases, vinylamine and furan. The preferred site for protonation of the substrates appears to be determined primarily by the ability of the protonated species (BH+) to delocalize the acquired positive charge. On the other hand, localization of a pair of electrons at a proton-acceptor site of B tends to be more important in determining the preferred site for hydrogen bonding with HF. The behavior of acids stronger than HF lies between these extremes. Consistent with a previously proposed Hammond postulate for complexes, when a substrate (B) interacts with a range of acids (AH+), proton transfer is generally found to occur when the proton affinity of A is significantly less than that of B. When the proton affinity of A is greater than that of B, a hydrogen-bonded complex is generally formed without proton transfer. Strongest binding (relative to the lowest energy components) occurs when the proton affinities of A and B are comparable. Proton transfer from AH+ is found to take place in some cases when this would not be predicted on the basis of protonation energies alone, because of specific interactions in the resulting complexes.     

Structural rationalisation of co-crystals formed between trithiocyanuric acid and molecules containing hydrogen bonding functionality

Crystallisation of trithiocyanuric acid (TTCA) from various organic solvents that have hydrogen bonding capability (acetone, 2-butanone, dimethylformamide, dimethyl sulfoxide, methanol and acetonitrile) leads to the formation of co-crystals in which the solvent molecules are incorporated together with TTCA in the crystal structure. Structure determination by single-crystal X-ray diffraction reveals that these co-crystals can be classified into different groups depending upon the topological arrangement of the TTCA molecules in the crystal structure. Thus, three different types of single-tape arrangements of TTCA molecules and one type of double-tape arrangement of TTCA molecules are identified. In all co-crystals, hydrogen-bonding interactions are formed through the involvement of N-H bonds of TTCA molecules in these tapes and the other molecule in the co-crystal. Detailed rationalisation of the structural properties of these co-crystals is presented.     

On the strength of hydrogen bonding within water clusters on the coordination limit

Hydrogen bonds (HB) are arguably the most important noncovalent interactions in chemistry. We study herein how differences in connectivity alter the strength of HBs within water clusters of different sizes. We used for this purpose the interacting quantum atoms energy partition, which allows for the quantification of HB formation energies within a molecular cluster. We could expand our previously reported hierarchy of HB strength in these systems (Phys. Chem. Chem. Phys., 2016, 18 , 19557) to include tetracoordinated monomers. Surprisingly, the HBs between tetracoordinated water molecules are not the strongest HBs despite the widespread occurrence of these motifs (e.g., in ice I_h). The strongest HBs within H₂O clusters involve tricoordinated monomers. Nonetheless, HB tetracoordination is preferred in large water clusters because (a) it reduces HB anticooperativity associated with double HB donors and acceptors and (b) it results in a larger number of favorable interactions in the system. Finally, we also discuss (a) the importance of exchange-correlation to discriminate among the different examined types of HBs within H₂O clusters, (b) the use of the above-mentioned scale to quickly assess the relative stability of different isomers of a given water cluster, and (c) how the findings of this research can be exploited to indagate about the formation of polymorphs in crystallography. Overall, we expect that this investigation will provide valuable insights into the subtle interplay of tri- and tetracoordination in HB donors and acceptors as well as the ensuing interaction energies within H₂O clusters.     

The hydrogen bonding properties of cytosine: a computational study of cytosine complexed with hydrogen fluoride, water, and ammonia

Density functional theory is used to study the hydrogen bonding pattern in cytosine, which does not contain alternating proton donor and acceptor sites and therefore is unique compared with the other pyrimidines. Complexes between various small molecules (HF, H(2)O, and NH(3)) and four main binding sites in (neutral and (N1) anionic) cytosine are considered. Two complexes (O2(N1) and N3(N4)) involve neighboring cytosine proton acceptor and donor sites, which leads to cooperative interactions and bidendate hydrogen bonds. The third (less stable) complex (N4) involves a single cytosine donor. The final (O2-N3) complex involves two cytosine proton acceptors, which leads to an anticooperative hydrogen bonding pattern for H(2)O and NH(3). On the neutral surface, the anticooperative O2-N3 complex is less stable than those involving bidentate hydrogen bonds, and the H(2)O complex cannot be characterized when diffuse functions are included in the (6-31G(d,p)) basis set. On the contrary, the anionic O2-N3 structure is the most stable complex, while the HF and H(2)O N3(N4) complexes cannot be characterized with diffuse functions. B3LYP and MP2 potential energy surface scans are used to consider the relationship between the water N3(N4) and O2-N3 complexes. These calculations reveal that diffuse functions reduce the conversion barrier between the two complexes on both the neutral and anionic surfaces, where the reduction leads to a (O2-N3) energy plateau on the neutral surface and complete (N3(N4)) complex destabilization on the anionic surface. From these complexes, the effects of hydrogen bonds on the (N1) acidity of cytosine are determined, and it is found that the trends in the effects of hydrogen bonds on the (N1) acidity are similar for all pyrimidines.     

Quantum energy flow and the kinetics of water shuttling between hydrogen bonding sites on trans-formanilide

A potential energy surface for trans-formanilide (TFA)-H2O is calculated and applied to study energy flow in the complex as well as the kinetics of water shuttling between hydrogen bonding sites on TFA. In addition to the previously identified H2O-TFA(C[Double Bond]O) and H2O-TFA(NH) minima, with the water monomer bound to the C[Double Bond]O and NH groups, respectively, the new surface reveals a second local minimum with the water bound to the C[Double Bond]O group, and which lies energetically 310 cm(-1) above the previously identified H2O-TFA(C[Double Bond]O) global minimum. On this surface, the energy barrier for water shuttling from H2O-TFA(C[Double Bond]O) global minimum to H2O-TFA(N-H) is 984 cm(-1), consistent with the experimental bounds of 796 and 988 cm(-1) [J. R. Clarkson et al. Science 307, 1443 (2005)]. The ergodicity threshold of TFA is calculated to be 1450 cm(-1); for the TFA-H2O complex, the coupling to the water molecule is found to lower the ergodicity threshold to below the isomerization barrier. Energy transfer between the activated complex and the vibrational modes of TFA is calculated to be sufficiently rapid that the Rice-Ramsperger-Kassel-Marcus (RRKM) theory does not overestimate the rate of water shuttling. The possibility that the rate constant for water shuttling is higher than the RRKM theory estimate is discussed in light of the relatively high energy of the ergodicity threshold calculated for TFA.     

Studies in hydrogen bonding: simulation of the crystalline solids of ice, ammonia, and ammonia hydrate

The crystal structures of ice, ammonia and ammonia hydrate have been simulated with rigid molecules using the interatomic potential function EPEN/2 and the computer program WMIN. Structural parameters were adjusted to give structures with minimum energy. The hydrogen bonding in the simulated structures is compared with that in the experimental structures.     

Interplay between anion-pi and hydrogen bonding interactions

The interplay between two important noncovalent interactions involving aromatic rings is studied by means of high level ab initio calculations. They demonstrate that synergistic effects are present in complexes where anion-pi and hydrogen bonding interactions coexist. These synergistic effects have been studied using the "atoms-in-molecules" theory and the Molecular Interaction Potential with polarization partition scheme. The present study examines how these two interactions mutually influence each other.     

IR spectroscopic study of the complex formation between ammonia and water molecules in a KBr matrix

The formation of complexes of ammonia and water molecules in a potassium bromide matrix is studied by means of IR spectroscopy. Ammonia and water complexes of variable composition are stabilized in a solid matrix using different approaches to saturating KBr powder with the initial components. Proton transfer can occur, leading to the formation of ammonium salts.     

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.     

Matrix isolation infrared and ab initio study of the hydrogen bonding between formic acid and water

The infrared spectra of the formic acid-water complexes isolated in argon matrices are reported. Both supersonic jet expansion and a conventional effusive source followed by trapping in solid argon at 10K are used to obtain the matrices. The experimental IR spectra are compared to the data obtained from high level ab initio (MP2) and DFT (B3LYP) calculations with 6-311++G(d,p) and aug-cc-pVTZ basis sets. The complex formation results in red shifts in the C=O and O-H stretching vibrations and a blue shift in the C-O stretching vibration of formic acid. The O-H stretching modes of water also exhibit pronounced red shifts. Both the MP2 and B3LYP calculations located three minima corresponding to cyclic HCOOH...H2O complexes with two hydrogen bond interactions. The binding energies are -10.3, -5.1, and -3.5 kcal mol(-1), respectively, for the three complexes at the MP2/ aug-cc-pVTZ level, corrected for the basis set superposition error (BSSE) using the Boys-Bernardi counterpoise scheme. Comparison of the calculated frequencies of the three complexes with the matrix IR spectrum reveals that the lowest energy complex is formed. In addition, a complex of formic acid with two water molecules is observed.     

Pseudopotential studies of the water and hydrogen fluoride molecules

A model pseudopotential is used to calculate valence electron properties for H₂O and HF. The calculated geometries, force constants, and ionization potentials are in excellent agreement with the results of corresponding all-electron calculations.     

On transport properties of hot liquid and supercritical water and their relationship to the hydrogen bonding

The dynamic viscosity η of water at temperatures along the saturation line is fitted with an expression taking into account the relative void volume, the enthalpy of vaporization, and the hydrogen bonding, the latter through the Kirkwood dipole orientation correlation parameter, g_K. A similar expression is given for the fitting of viscosity data of supercritical water, except that the explicit temperature dependence of ln η on 1/RT is now negative. The self-diffusion coefficients D of water along the saturation line up to the critical point are shown to depend on the fractions of non- and singly hydrogen-bonded water molecules. The high pressure (110 MPa) values of D of supercritical water are a smooth extension of the values for lower temperature water at the same pressure.     

Intra- and intermolecular hydrogen bonding in formohydroxamic acid complexes with water and ammonia: infrared matrix isolation and theoretical study

The complexes of formohydroxamic acid with water and ammonia have been studied using FTIR matrix isolation spectroscopy and MP2 calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra of the HCONHOH/H₂O(NH₃)/Ar matrixes indicates formation of strongly hydrogen-bonded complexes in which the NH group of formohydroxamic acid acts as a proton donor toward the oxygen atom of water or the nitrogen atom of ammonia. The NH stretching vibration of formohydroxamic acid exhibits 150 cm⁻¹ red shift in the complex with water and 443 cm⁻¹ red shift in the complex with ammonia as compared to the NH stretch of the HCONHOH monomer. The theoretical calculations indicate stability of five isomers for the water complex and three isomers for the ammonia complex. The most stable are the cyclic structures in which the water or ammonia molecules are inserted within the intramolecular hydrogen bond of the formohydroxamic acid molecule and act as proton donors for the CO group and proton acceptors for the OH group of the formohydroxamic acid molecule. In spite of their stability the cyclic structures have not been observed in the matrixes which indicates high energy barrier for their formation, the reaction of complex formation is under kinetic and not thermodynamic control.