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Three dynamic continuum approaches for solvation were used to calculate the time correlation functions of the solvent relaxation of the coumarin-153 molecule and benzophenone anion in acetonitrile. The approaches are the local model with double molecular-shaped cavity, a new local model with a double-molecular shaped cavity and a nonlocal model with a spherical cavity. Results showed that both local models displayed oscillations in the shorter time region t < 1 ps. Moreover, the nonlocal dynamic theory was not able to suppress the oscillations.

Two new peroxosolvates of drug-like compounds were synthesized and studied by a combination of X-ray crystallographic, Raman spectroscopic methods, and periodic DFT computations. The enthalpies of H-bonds formed by hydrogen peroxide (H2O2) as a donor and an acceptor of protons were compared with the enthalpies of analogous H-bonds formed by water (H2O) in isomorphic (isostructural) hydrates. The enthalpies of H-bonds formed by H2O2 as a proton donor turned out to be higher than the values of the corresponding H-bonds formed by H2O. In the case of H2O2 as a proton acceptor in H-bonds, the ratio appeared reversed. The neutral O∙∙∙H-O/O∙∙∙H-N bonds formed by the lone electron pair of the oxygen atom of water were the strongest H-bonds in the considered crystals. In the paper, it was found out that the low-frequency Raman spectra of isomorphous crystalline hydrate and peroxosolvate of N-(5-Nitro-2-furfurylidene)-1-aminohydantoin are similar. As for the isostructural hydrate and peroxosolvate of the salt of protonated 2-amino-nicotinic acid and maleic acid monoanion, the Raman spectra are different. [ABSTRACT FROM AUTHOR]

Thestructure, IR harmonic frequencies and intensities of normal vibrationsof 20 molecular crystals with the X–Cl···Cl–Xcontacts of different types, where X = C, Cl, and F and the Cl···Cldistance varying from ∼3.0 to ∼4.0 Å, are computedusing the solid-state DFT method. The obtained crystalline wave functionshave been further used to define and describe quantitatively the Cl···Clinteractions via the electron-density features at the Cl···Clbond critical points. We found that the electron-density at the bondcritical point is almost independent of the particular type of thecontact or hybridization of the ipso carbon atom. The energy of Cl···Clinteractions, Eint, is evaluated fromthe linking Eintand local electronickinetic energy density at the Cl···Cl bond criticalpoints. Eintvaries from 2 to 12 kJ/mol.The applicability of the geometrical criterion for the detection ofthe Cl···Cl interactions in crystals with two or moreintermolecular Cl···Cl contacts for the unique chlorineatom is not straightforward. The detection of these interactions insuch crystals may be done by the quantum-topological analysis of theperiodic electron density. [ABSTRACT FROM AUTHOR]

Hydrogen bonding in ionic liquids based on the 1-(2′-hydroxylethyl)-3-methylimidazoliumcation ([C2OHmim]+) and various anions ([A]−) of differing H-bond acceptor strength, viz. hexafluorophosphate[PF6]−, tetrafluoroborate [BF4]−, bis(trifluoromethanesulfonimide) [Tf2N]−, trifluoromethylsulfonate [OTf]−, and trifluoroacetate [TFA]−, was studied by arange of spectroscopic and computational techniques and, in the caseof [C2OHmim][PF6], by single crystal X-ray diffraction.The first quantitative estimates of the energy (EHB) and the enthalpy (−ΔHHB) of H-bonds in bulk ILs were obtained from a theoreticalanalysis of the solid-state electron-density map of crystalline [C2OHmim][PF6] and an analysis of the IR spectra incrystal and liquid samples. EHBfor OH···[PF6]−H-bonds amounts to ∼3.4–3.8kcal·mol–1, whereas weaker H-bonds (2.8–3.1kcal·mol–1) are formed between aromatic C2Hgroup of imidazolium ring and the [PF6]−anion. The enthalpy of the OH···[A]−H-bonds follows the order: [PF6] (2.4 kcal·mol–1) < [BF4] (3.3 kcal·mol–1) < [Tf2N] (3.4 kcal·mol–1)< [OTf] (4.7 kcal·mol–1l) < [TFA] (6.2kcal·mol–1). The formation of aggregates ofself-associated [C2OHmim]+cations is presentin liquid [C2OHmim][PF6], [C2OHmim][BF4], and [C2OHmim][Tf2N], with the energyof the OH···OH H-bonds amounting to ∼6 kcal·mol–1. Multiple secondary interactions in the bulk ILsinfluence their structure, vibrational spectra, and H-bond strength.In particular, these interactions can blue-shift the stretching frequenciesof the CH groups of the imidazolium ring in spite of red-shiftingCH···[A]−H-bonds. They also weakenthe H-bonding in the IL relative to the isolated ion pairs, with theseanticooperative effects amounting to ca. 50% of the EHBvalue. [ABSTRACT FROM AUTHOR]

The structure, IR spectrum, and H-bond network in the serine-H2O and serine-H2O2 crystals were studied using DFT computations with periodic boundary conditions. Two different basis sets were used: the all-electron Gaussian-type orbital basis set and the plane wave basis set. Computed frequencies of the IR-active vibrations of the titled crystals are quite different in the range of 10-100 cm-1. Harmonic approximation fails to reproduce IR active bands in the 2500-2800 frequency region of serine-H2O and serine-H2O2. The bands around 2500 and 2700 cm-1 do exist in the anharmonic IR spectra and are caused by the first overtone of the OH bending vibrations of H2O and a combination vibration of the symmetric and asymmetric bendings of H2O2. The quantum-topological analysis of the crystalline electron density enables us to describe quantitatively the H-bond network. It is much more complex in the title crystals than in a serine crystal. Appearance of water leads to an increase of the energy of the amino acid-amino acid interactions, up to 50 kJ/mol. The energy of the amino acid-water H-bonds is 30 kJ/mol. The H2O/H2O2 substitution does not change the H-bond network; however, the energy of the amino acid-H2O2 contacts increases up to 60 kJ/mol. This is caused by the fact that H2O2 is a much better proton donor than H2O in the title crystals. [ABSTRACT FROM AUTHOR]

Despite the technological importance of urea perhydrate (percarbamide) and sodium percarbonate, and the growing technological attention to solid forms of peroxide, fewer than 45 peroxosolvates were known by 2000. However, recent advances in X-ray diffractometers more than tripled the number of structurally characterized peroxosolvates over the last 20 years, and even more so, allowed energetic interpretation and gleaning deeper insight into peroxosolvate stability. To date, 134 crystalline peroxosolvates have been structurally resolved providing sufficient insight to justify a first review article on the subject. In the first chapter of the review, a comprehensive analysis of the structural databases is carried out revealing the nature of the co-former in crystalline peroxosolvates. In the majority of cases, the coformers can be classified into three groups: (1) salts of inorganic and carboxylic acids; (2) amino acids, peptides, and related zwitterions; and (3) molecular compounds with a lone electron pair on nitrogen and/or oxygen atoms. The second chapter of the review is devoted to H-bonding in peroxosolvates. The database search and energy statistics revealed the importance of intermolecular hydrogen bonds (H-bonds) which play a structure-directing role in the considered crystals. H2O2 always forms two H-bonds as a proton donor, the energy of which is higher than the energy of analogous H-bonds existing in isostructural crystalline hydrates. This phenomenon is due to the higher acidity of H2O2 compared to water and the conformational mobility of H2O2. The dihedral angle H-O-O-H varies from 20 to 180° in crystalline peroxosolvates. As a result, infinite H-bonded 1D chain clusters are formed, consisting of H2O2 molecules, H2O2 and water molecules, and H2O2 and halogen anions. H2O2 can form up to four H-bonds as a proton acceptor. The third chapter of the review is devoted to energetic computations and in particular density functional theory with periodic boundary conditions. The approaches are considered in detail, allowing one to obtain the H-bond energies in crystals. DFT computations provide deeper insight into the stability of peroxosolvates and explain why percarbamide and sodium percarbonate are stable to H2O2/H2O isomorphic transformations. The review ends with a description of the main modern trends in the synthesis of crystalline peroxosolvates, in particular, the production of peroxosolvates of high-energy compounds and mixed pharmaceutical forms with antiseptic and analgesic effects. [ABSTRACT FROM AUTHOR]

The structures, relative stability, infrared (IR) and Raman spectra of the most-stable forms of [H9O4]+ and [H13O6]+ ions in acetonitrile are computed using the B3LYP functional combined with the Polarizable Continuum Model approximation. These forms are hydrated [H3O]+ and [H5O2]+ cores. Of interest are two main environmental effects on the spectroscopic features of protonated water hydrates: (i) polarization of the solvent by the hydrate dipole moment; (ii) formation of H-bonds with bulky counterions (ClO4- and BF4-). The effect of the polarization on the structure of the [H3O]+ core strongly depends on the symmetry of the hydration shell. A distortion of a hydrated [H3O]+ easily changes its structure to the [H7O3]+ one that causes a change in the nature of the most IR-intensive bands. Thus, the specificity of this core can be easily lost that prevents identification of the corresponding species. By contrast, the [H5O2]+ core is more stable against distortion. It is characterized by the short O…O distance (< 2.45 Å), IR-intensive band near 1720 cm-1 and Raman-intensive line around 500 cm-1. The [H5O2]+ core remains identifiable even when protonated hydrate is involved in specific interactions with a bulky counterion. Geometrical criteria for identification of the [H3O]+, [H5O2]+ and [H7O3]+ cores are discussed.

The structure and spectroscopic properties of the 1:1 complexes of substituted pyridines with benzoic acid and phenol derivatives in aprotic solvents are studied using B3LYP functional combined with the polarizable continuum model approximation. Two extreme structures are investigated: the state without (HB) and with proton transfer (PT). In the presence of an external electric field the O...N distance is contracted and the PT state does appear. The PT state of both the pyridine-benzoic and the pyridine-phenol complexes displays the only IR-active band in the 2800-1800 frequency region, which is located around 2000 cm(-1). However, the nature of the band is different for these two complexes. In the pyridine-benzoic acid complex it is practically a pure stretching vibration of the HN(+) group, while in the pyridine-phenol complex it is the mixed vibration of the bridging proton. A specific feature of the PT state in the pyridine-phenol complex is an IR-intensive band near 600 cm(-1), associated with the asymmetric stretching vibrations of the O(-)...HN(+) fragment. Its intensity is reciprocally proportional to the O...N distance. The appearance of this band provides an efficient criterion to differentiate between the HB and PT states of the 1:1 complexes of phenols with pyridines in aprotic solvents.