OH Stretching Frequency Shifts Research Articles

Probing the Effects of Size and Charge on the Monohydration and Dihydration of SiF5- and SiF62- via Comparisons with BF4- and PF6.

This study systematically examines the interactions of the trigonal bipyramidal silicon pentafluoride and octahedral silicon hexafluoride anions with either one or two water molecules, (SiF5-(H2O)n and SiF62-(H2O)n, respectively, where n = 1, 2). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed using the CCSD(T) ab initio method with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for Si, O, and F; denoted as haTZ). Two monohydrate and six dihydrate minima have been identified for the SiF5-(H2O)n systems, whereas one monohydrate and five dihydrate minima have been identified for the SiF62-(H2O)n systems. Both monohydrated anions have a minimum in which the water molecule adopts a symmetric double ionic hydrogen bond (DIHB) motif with C2v symmetry. However, a second unique monohydrate minimum has been identified for SiF5- in which the water molecule adopts an asymmetric DIHB motif along the edge of the trigonal bipyramidal anion between one axial and one equatorial F atom. This Cs structure is more than 2 kcal mol-1 lower in energy than the C2v local minimum at the CCSD(T)/haTZ level of theory. While the interactions between the solvent and ionic solute are quite strong for the monohydrated anions (electronic dissociation energies of ≈12 and ≈24 kcal mol-1 for the SiF5-(H2O)1 and SiF62-(H2O)1 global minima, respectively), these values are nearly perfectly doubled for the dihydrates, with the lowest-energy SiF5-(H2O)2 and SiF62-(H2O)2 minima exhibiting dissociation energies of ≈24 and ≈47 kcal mol-1, respectively. Structures that form hydrogen bonds between the solvating water molecules also exhibit the largest shifts in the harmonic OH stretching frequencies for the waters of hydration. These shifts can exceed -100 cm-1 for the SiF5-(H2O)2 minimum and -300 cm-1 for the SiF62-(H2O)2 minimum relative to an isolated H2O molecule at the CCSD(T)/haTZ level of theory. This work also corrects the OH stretching frequency shifts for two dihydrate minima of PF6- that were previously erroneously reported ( J. Phys. Chem. A 2020, 124, 8744-8752, DOI: 10.1021/acs.jpca.0c06466).

Molecular Hydrogen Acts as a Hydrogen Bond Proton Acceptor: From Protonated Betaine Tagging to the Weakest Hydrogen Bond.

In an attempt to gain further insights into the intermolecular interactions implied by Rizzo's group's cautionary tale related to molecular tagging in infrared multiple photon dissociation (IRMPD) spectroscopy with molecular messengers [Masson, A. . J. Chem. Phys. 2015, 143, 104313], in the present study, we provide an in-depth analysis of the noncovalent interaction between the molecular hydrogen and protonated betaine molecule in the gas phase. We aim to shed some new light on the fundamental issues concerning the wide diapason of hydrogen-bonding-type intermolecular interactions, with a wide variety of proton acceptors. We demonstrate that in the course of tagging the protonated betaine with molecular hydrogen from the OH group side, it is the σ bond of molecular hydrogen that plays the role of hydrogen-bonding proton acceptor. The tagging thus induces a small yet significant red shift of the protonated betaine O-H stretching mode. We investigate the performance of a wide range of density functional theory (DFT) functionals for the calculation of anharmonic vibrational frequency shifts of the studied system, which are essential for the correct interpretation of the experimental IRMPD data. For an accurate prediction of the OH stretching frequency shifts, specifically designed functionals such as Handy's group HCTH/407 should be applied. The empirical dispersion correction enhances the systematic overestimation of the anharmonic frequency shift, characteristic of the most widely used DFT functionals. Combining the full-wave function approach with the charge field perturbation and natural bond orbital (NBO) deletion analyses, we demonstrate that the frequency shift in the OH-tagged structure is governed by the σHH → σ*OH intermolecular charge transfer. This interaction stabilizes the OH-tagged dimer as well, in contrast to the dipole-quadrupole electrostatic interaction energy term. Topological analysis of the electron density reveals the presence of an intermolecular bond critical point with a positive value of the density Laplacian very close to the lower limit for hydrogen bonds. NCI analyses demonstrate that the OH···H2 interaction is weaker than the intramolecular CH···O one within the protonated betaine molecule, with the through of reduced density gradient appearing at less negative sign(λ2)·ρ values. Analyzing the O-H stretching vibrational potential with the second-generation absolutely localized molecular orbitals energy decomposition analysis (ALMO-EDA 2) revealed that in the case of betaineH(+) tagged from the OH group side, the permanent electrostatics (ΔEelec), polarization (ΔEpol), and charge-transfer (ΔEct) contributions to the total intermolecular interaction energy contribute favorably to the weak hydrogen bond formation and to the red shift of the fundamental O-H stretching frequency, the ΔEct contribution being the most significant in the last context. The Pauli repulsion term, on the other hand, favors an O-H stretching frequency blue shift as a consequence of the vibrational confinement effects.

A quantum chemical computational insight into the intramolecular hydrogen bond interaction in an antibacterial drug molecule-2-acetylindan-1,3-dione

A Density Functional Theory (DFT)-based quantum chemical computational study has been carried out to characterize the intramolecular hydrogen bonding (IMHB) interaction in a potent bio-active drug molecule viz., 2-acetylindan-1,3-dione (2-AID). The IMHB interaction has been explored by calculation of electron density ρ(r) and Laplacian ∇2ρ(r) at the Bond Critical Point (BCP) using Atoms-In-Molecule (AIM) theory. Topological features, energy densities provided by AIM theory are calculated with ρ(r) for a number of intramolecular H-bond distances. The results suggest that at equilibrium geometry the IMHB interaction in the molecule develops certain characteristics typical of covalent interaction. The role of hyperconjugative charge transfer interaction in the IMHB has been critically evaluated and addressed under the provision of Natural Bond Orbital (NBO) analysis. The study also pays proper attention to an important feature of IMHB interaction, namely the directional nature, within the NBO framework in a consensus manner. Simulated IR spectra also provide reinforcing evidence for IMHB interaction on the basis of OH stretching frequency shift. The optimized geometry features, molecular electrostatic potential (MEP) map analysis are also found to produce a consensus view in relation with the formation of IMHB in 2-AID.

Ultrafast OH-stretching frequency shifts of hydrogen- bonded 2-naphthol photoacid-base complexes in solution

We characterize the transient solvent-dependent OH-stretching frequency shifts of photoacid 2-naphthol hydrogen-bonded with CH3CN in the S0- and S1-states using a combined experimental and theoretical approach, and disentangle specific hydrogen-bonding contributions from nonspecific dielectric response.

Anharmonic Vibrational Frequency Shifts upon Interaction of Phenol(+) with the Open Shell Ligand O2. The Performance of DFT Methods versus MP2

Anharmonic vibrational frequency shifts of the phenol(+) O-H stretching mode upon complex formation with the open-shell ligand O(2) were computed at several DFT and MP2 levels of theory, with various basis sets, up to 6-311++G(2df,2pd). It was found that all DFT levels of theory significantly outperform the MP2 method with this respect. The best agreement with the experimental frequency shift for the hydrogen-bonded minimum on the potential energy surfaces was obtained with the HCTH/407 functional (-93.7 cm(-1) theoretical vs -86 cm(-1) experimental), which is a significant improvement over other, more standard DFT functionals (such as, e.g., B3LYP, PBE1PBE), which predict too large downshifts (-139.9 and -147.7 cm(-1), respectively). Good agreement with the experiment was also obtained with the mPW1B95 functional proposed by Truhlar et al. (-109.2 cm(-1)). We have attributed this trend due to the corrected long-range behavior of the HCTH/407 and mPW1B95 functionals, despite the fact that they have been designed primarily for other purposes. MP2 method, even with the largest basis set used, manages to reproduce only less than 50% of the experimentally detected frequency downshift for the hydrogen-bonded dimer. This was attributed to the much more significant spin contamination of the reference HF wave function (compared to DFT Kohn-Sham wave functions), which was found to be strongly dependent on the O-H stretching vibrational coordinate. All DFT levels of theory outperform MP2 in the case of computed anharmonic OH stretching frequency shifts upon ionization of the neutral phenol molecule as well. Besides the hydrogen-bonded minimum, DFT levels of theory also predict existence of two other minima, corresponding to stacked arrangement of the phenol(+) and O(2) subunits. mPW1B95 and PBE1PBE functionals predict a very slight blue shift of the phenol(+) O-H stretching mode in the case of stacked dimer with the nearly perpendicular orientation of oxygen molecule with respect to the phenolic ring, which is entirely of electrostatic origin, in agreement with the experimental observations of an additional band in the IR photodissociation spectra of phenol(+)-O(2) dimer [Patzer, A.; Knorke, H.; Langer, J.; Dopfer, O. Chem. Phys. Lett. 2008, 457, 298]. The structural features of the minima on the studied PESs were discussed in details as well, on the basis of NBO and AIM analyses.

A computational insight into the photophysics of a potent UV absorber Tinuvin P: Critical evaluation of the role of charge transfer interaction and topological properties of the intramolecular hydrogen bonding

In the present contribution, we report a computational investigation using Density Functional Theory (DFT) method on the photophysics of a potent UV absorber (UVA) Tinuvin P (2-(2-hydroxy-5-methylphenyl)benzotriazole). Since the exceptional photostability of such UVAs is principally banked upon their ability to undergo excited-state deactivation via an ultrafast excited-state proton transfer (ESIPT) mechanism, emphasis has been rested on this particular mode of excited-state deactivation of Tinuvin P (TIN P). The operation of ESIPT has been most critically argued on the lexicon of potential energy surface (PES) across the reaction coordinate and cross-validated from frontier molecular orbital (MO) analysis. Evolution of other geometrical parameters during the course of the ESIPT process in TIN P has been crucial to delve into the mechanistic details of the process. Major emphasis of the work is rendered on the analysis of the intramolecular hydrogen bonding (IMHB) interaction in TIN P. The IMHB interaction has been explored by calculation of electron density ρ( r) and Laplacian ∇ 2 ρ( r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM). Concomitantly, the role of charge transfer interaction in the IMHB has been critically evaluated and addressed under the provision of natural bond orbital (NBO) analysis. Simulated IR spectra also provide reinforcing evidence for IMHB interaction on the basis of OH stretching frequency shift.

On the Assessment of Some New Meta-Hybrid and Generalized Gradient Approximation Functionals for Calculations of Anharmonic Vibrational Frequency Shifts in Hydrogen-Bonded Dimers

The performance of some recently proposed DFT functionals by Truhlar's group (mPW1B95, mPWLYP1W, PBELYP1W, and PBE1W [Dahlke, E. E.; Truhlar, D. G. J. Phys. Chem. B 2005, 109, 317. Zhao, Y.; Truhlar, D. G. J. Phys. Chem. A 2004, 108, 6908.]) was tested primarily with respect to computation of anharmonic vibrational frequency shifts upon hydrogen bond formation in small molecular/ionic dimers. Five hydrogen-bonded systems with varying hydrogen bond strengths were considered: methanol-fluorobenzene, phenol-carbon monoxide in ground neutral (S(0)) and cationic (D(0)) electronic states, phenol-acetylene, and phenol-benzene(+). Anharmonic OH stretching frequency shifts were calculated from the computed vibrational potentials for free and hydrogen-bonded proton-donor molecules. To test the basis set convergence properties, all calculations were performed with 6-31++G(d,p) and 6-311++G(2df,2pd) basis sets. The mPW1B95 functional was found to perform remarkably better in comparison to more standard functionals (such as B3LYP, mPW1PW91, PBE1PBE) in the case of neutral dimers. In the case of cationic dimers, however, this is not always the case. With respect to prediction of anharmonic OH stretching frequency shifts upon ionization of free phenol, all DFT levels of theory outperform MP2. Some other aspects of the functional performances with respect to computation of interaction and dissociation energies were considered as well.

Raman OH stretching frequency shifts in supercritical water and in O 2- and acetone-aqueous solutions near the water critical point

Raman OH stretching frequency shifts in supercritical water and in O 2- or acetone- aqueous solutions near the water critical point were observed to discuss the microscopic solution structure of these fluids. In neat water, the peak frequencies shifted almost linearly to the density except near the critical density. As the temperature approached the critical temperature, the density dependence of the shift became non-linear. This behavior was considered to be due to some microscopic structural non-uniformity caused by the density fluctuation. In the solutions, such non-linear density dependences were decreased, suggesting the decrease in the local density augmentation around water molecules.

Relating linear vibrational spectroscopy to condensed-phase hydrogen-bonded structures: Liquid-to-supercritical water

The pressure and temperature-dependent linear absorption spectrum of partially deuterated water HOD dissolved in heavy water D(2)O was measured in the OH-stretching spectral region. The temperature was varied in the interval of 298 K</=T</=700 K while the density was changed within the range of 12 moll</=rho</=58 moll corresponding to the liquid and the supercritical phases of the fluid solution. The spectra were analyzed in terms of the temperature and density dependent frequency of maximal absorbance nu(max)(T,rho) and their full widths at half maximum Deltanu(T,rho). In parallel, molecular dynamics simulations of the fluid solution were carried out to obtain the average nearest neighbor O-O distance r(OO) ((1))(T,rho) and its dispersion Deltar(OO) ((1))(T,rho) at any state point (T,rho) for which an absorption spectrum was recorded. A correlation is presented between the experimental spectroscopic quantities nu(max)(T,rho) and Deltanu(T,rho) on the one hand and the local structural quantities r(OO) ((1))(T,rho) and Deltar(OO) ((1))(T,rho) on the other. This intuitive correlation can be used as a critical test for future perturbational simulations of the OH-stretching frequency shifts with hydrogen-bond geometry. Finally, a connection is made to the average hydrogen-bond connectivity in the fluid via the temperature and density dependent dielectric constant of water.

Experimental study of the NaCl–H 2O system up to 28 GPa: Implications for ice-rich planetary bodies

Recent studies have hypothesized that high-pressure H 2O polymorphs, specifically Ice VI and Ice VII, make up a significant portion of the interiors of select outer planets and their moons; most notably the Galilean satellites, Saturn's Titan and possibly Neptune's moon Triton as well as potential H 2O-rich extra-solar bodies. Several of these bodies have been conjectured to contain subsurface salty H 2O waters; therefore, any potential ice phases in the interior of these satellites could have interacted extensively with the salty oceans. Raman spectroscopy and synchrotron radiation have been used previously to study the bonding structure and unit cell parameters of pure Ice VII. However, no data exist on the effect of salts on the unit cell parameters and volume of solid H 2O at high pressure. To obtain pertinent data for use in planetary physics, it is important to understand the effect of impurities on H 2O at high pressure. The NaCl–H 2O system was chosen as a first order approximation of H 2O-rich planetary bodies. The unit cell parameters and OH stretching frequencies of Ice VII formed from 5 and 10 wt.% NaCl–H 2O solutions were studied in detail up to 27 GPa at 298 K by using a diamond anvil cell, synchrotron X-ray radiation and Raman spectroscopy. The data indicate that, over the range in pressure and temperature of this study, the maximum solubility of solutes in Ice VII was not pressure dependent. Our data suggest that the maximum concentration of NaCl that can be incorporated into Ice VII at 298 K is 7.5 ± 2.5 wt.% (or 2.4 ± 0.8 mol% NaCl). Ice VII formed from a 5 wt.% NaCl–H 2O solution has a density that is up to 5% greater at any given pressure relative to the density of Ice VII formed from pure H 2O. Additionally, the bulk modulus, 26.2 ± 1.4 GPa, was found to be approximately 10–20% greater relative to Ice VII formed from pure H 2O. Relative OH stretching frequency shifts from Ice VII formed from the NaCl–H 2O solutions were compared to Ice VII formed from pure H 2O. Ice VII formed from a 5 wt.% NaCl–H 2O solution shows a systematic increase of approximately 15 rel cm −1 in the OH stretching frequency relative to pure Ice VII for any given pressure. We hypothesize that the incorporation of Na + and Cl − into the body centered cubic structure of Ice VII results in systematic variations in the intensive thermodynamic properties of Ice VII formed from low salinity solutions. These new data will provide an improved first order approximation of high-pressure H 2O phases found within H 2O-rich bodies and should be used to model the density profiles of H 2O-rich bodies.

The case of a very weakly π-hydrogen bonded fluorobenzene–methanol complex. A gradient-corrected density functional and MP2 study of the ground electronic state potential energy surface

The π-hydrogen bonded minimum on the standard and the counterpoise-corrected B3LYP, PBE1PBE/6-31++G(d,p) and MP2/6-31++G(d,p) potential energy hypersurfaces of the methanol–fluorobenzene dimer is studied. Anharmonic OH stretching frequency shift calculated at MP2 level is in excellent agreement with the experiment (20.5 vs. 20 cm −1), while all DFT values are too large, the B3LYP results being superior to the PBE1PBE ones, especially for the counterpoise-corrected PES. The OH stretching vibrational potentials are analyzed with the charge field perturbation methodology. Interaction and dissociation energy calculations, along with the NBO and AIM analyses of the MP2 and Kohn–Sham densities are carried out as well.

Correlations between experimental matrix-isolation FT-IR and DFT(B3LYP) calculated data for isolated 1:1 H-bonded complexes of water and pyridine or imidazole derivatives

Relations between selected experimentally observed matrix isolation FT-IR and/or DFT(B3LYP)/6-31++G** predicted parameters are investigated for a series of 1:1 water complexes of pyridine and imidazole derivatives. Regular correlations are observed for: (i) the experimental and calculated OH stretching frequency shifts; (ii) the ratio between the observed and calculated IR stretching frequencies of the water OH group involved in the hydrogen bond and the proton affinity of the hydrogen bonding site (N atom) of the base; (iii) the H-bond interaction energy and the OH stretching frequency shift; (iv) the calculated OH and N⋯H distances and the interaction energy of the H-bond; and (v) the interaction energy of the H-bond and the square root of the intensity enhancement of the OH stretching mode. These correlations are restricted to structurally similar systems (i.e. to the pyridine or the imidazole analogs). These correlations demonstrate that the DFT(B3LYP) method is very suitable to predict trends in the parameters related to the H-bonding.

Red- versus Blue-Shifting Hydrogen Bonds: Are There Fundamental Distinctions?

The OH covalent bond of conventional hydrogen bonds of the OH···O type undergoes a lengthening as a result of the complex formation, and the OH stretching frequency shifts to the red; the same is t...

Infrared Spectroscopy of Intramolecular Hydrogen-Bonded OH Stretching Vibrations in Jet-Cooled Methyl Salicylate and Its Clusters

The OH stretching vibration of methyl salicylate and its solvated clusters in a supersonic free jet was observed by using fluorescence-detected infrared spectroscopy. The OH band of methyl salicylate monomer was weak and broad because of the intramolecular hydrogen bond. Those of the methyl salicylate moiety in small size hydrogen-bonded clusters with various solvent molecules, such as methyl salicylate−(H2O)n (n = 1 and 2), −CH3OH, and −NH3, also showed similar characteristics, indicating that the intramolecular hydrogen bond is retained even in the clusters. The opposite behavior of the direction of the electronic transition frequency shift and the OH stretching frequency shift was seen between the clusters with the acidic (water and methanol) and basic (ammonia) solvents. Structures for these clusters are discussed on the basis of the frequency shifts of the OH bond.

Repulsive and attractive interactions between Brnsted sites and hydrocarbon species with partial carbocationic character in restricted spaces: comparison of IR results and ab initiocalculations

A novel type of repulsive interaction between anchored oligomeric chains with partial carbocationic character (formed inside the channels of the zeolite upon proton catalyzed oligomerization of propene) and unreacted Brønsted groups in H-mordenite is described and discussed. This anomalous interaction causes the stretching frequency of the unreacted Brønsted groups to shift upwards (instead of downward as usually observed). This finding is compared with those obtained for the interaction of Brønsted groups with propene oligomers similarly formed in the channels of H-ZSM-5, H-β and H-Y and with those caused by the interaction of Brønsted groups with neutral molecules like n-heptane. In order to estimate both the value and the sign of the OH stretching frequency shift of the acidic site caused by the interaction with positively charged –(CH2)nCH3 chains, abinitio density functional calculations on a model compound have been performed to simulate the interaction of acidic centers with net and partially positively charged species.

Non-additivity of OH frequency shifts in ion-water systems

The intramolecular OH stretching frequency shift observed for water on formation of ‘cation-water…H-bond acceptor’ complexes is highly non-additive. The uncoupled OH frequency shift has been calculated by ab initio methods for q +-0H 2 and OH 2… q − complexes of different geometries and for a series of Mg 2+·(H 2O) n …(H 2O) m complexes, and we argue that the non-additivity (cooperativity) of the frequency shifts is largely a consequence of the parabolic shape of the frequency versus electric field curves.

Spectroscopic correlation for OH stretching frequency shifts of water in crystal hydrates

The shift of the uncoupled OH stretching frequency of water (from its free state position) in crystal hydrates has been plotted against a parameter r 0 obtained by subtracting the H-bond (OH...Y) length from the sum of the free state ionic radii of O and Y. From an analysis of this curve it is inferred that MO w coordination in hydrates reduces the ionic size of water oxygen and its effect on the OH stretching frequency is opposite to that of H-bonding.

Hydrogen bonding—V. Inductive effects on the ground state basicity of sulfones. The electronegativity of a covalently bound perchlorate group

OH stretching frequency shifts, Δν, have been determined for the hydrogen-bonded complexes between phenol and fifteen sulfones of the type p-CH 3C 6H 4SO 2 X ( X = methyl and substituted methyl). The Δν values can be linearly correlated with the ν asym SO 2 frequencies but not with the ν sym SO 2 frequencies of the sulfones. The substituent effect on Δν is primarily an inductive one and is a linear function of the Pauling electronegativities (“inductive constants”, π i ) and of the group electronegativities (χ p ) of X. The ν asym SO 2 frequencies of twenty-two sulfones ( p-CH 3C 6H 4SO 2 X) have been utilized to calculate π i values of X. From these data, the electronegativity of a covalently bound perchlorate moiety has been estimated and found to be comparable to that of the fluorine substituent.

Hydrogen bond studies: 79 . Correlation curves for properties of hydrogen bonded water molecules based on ab initio calculations

Correlation curves have been derived from previous ab initio MO-LCAO-SCF calculations made on water molecules in hydrates. The OH-stretching frequency shifts have been correlated with: (a) ratios of the intensity of v̄ v OH for bonded water to that for free water, (b) shifts in the OH-distances and (c) quadrupole coupling constants for deuterium in D 2O. Shifts in quadrupole coupling constants are also correlated with shifts in OH-distances. Comparisons have been made with experimental data and the agreement is found to be satisfactory.

Hydrogen bonding. Part IV: The ground state basicities of N,N‐disubstituted sulfinamides and sulfonamides

AbstractPhenol OH stretching frequency shifts, Δν, have been measured for the hydrogen‐bonded complexes between phenol and a series of N,N‐disubstituted sulfinamides and sulfonamides. The magnitudes of these Δν values indicate that the SO group is the acceptor site. The acceptor properties are interpreted chiefly in terms of inductive effects complemented by resonance effects involving π‐bonding between the sulfur and the nitrogen atom without significant alteration of the sulfur‐oxygen bond order.