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The halogen bonding in molecular crystals and supramolecular assemblies has been widely investigated. Special attention is given to the molecular structures capable of simultaneously exhibiting different types of non-covalent interactions, including conventional hydrogen bonds and halogen bonds. This paper systematically analyzes crystalline peroxosolvates of bispidine-based bis-amide derivatives, containing haloacetic acid residues, namely previously reported 1,1′-(1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-iodooethanone) peroxosolvate C13H20I2N2O2·H2O2 (1) and four new crystalline compounds, 1,1′-(1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-bromoethanone) peroxosolvate C13H20Br2N2O2·H2O2 (2), 1,1′-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-iodoethanone) peroxosolvate C13H20I2N2O5·0.5H2O2 (3), 1,1′-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-bromoethanone) peroxosolvate C13H20Br2N2O5·H2O2 (4), and 1,1′-(9-hydroperoxy-9-hydroxy-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane-3,7-diyl)bis(2-chloroethanone) peroxosolvate C13H20Cl2N2O5·H2O2 (5). Compounds 2–5 were synthesized for the first time and their crystal structures were determined by single-crystal X-ray diffractometry (SCXRD). To the best of our knowledge, 3–5 are unprecedented crystalline hydrogen peroxide adducts of organic hydroperoxides (R-OOH). Short intermolecular contacts between halogen and hydroperoxo oxygen atoms were found in 1–3. The halogen bonding of C–I(Br) fragments with dioxygen species in compounds 1–3 as well as in the previously reported cocrystal of diacetone diperoxide with triodotrinitrobenzene (6) was identified through reduced density gradient analysis, Hirshfeld surface analysis, and Bader analysis of crystalline electron density. The interactions were quantified using the electron density topological properties acquired from the periodic DFT calculations and evaluated to lie in the range of 9–19 kJ mol−1. A distinctive spectral feature was revealed for this type of interaction, involving a red shift of the characteristic O–O stretching vibration by about 6 cm−1, which appeared in IR spectra as a narrow low-intensity band in the region 837–872 cm−1. [ABSTRACT FROM AUTHOR]

Trimethylglycine (glycine betaine, GB) is an important organic osmolyte that accumulates in various plant species in response to environmental stresses and has significant potential as a bioactive agent with low environmental impact. It is assumed that the hydration of GB is playing an important role in the protective mechanism. The hydration and aggregation properties of GB have not yet been studied in detail at the atomistic level. In this work, noncovalent interactions in the GB dimer and its complexes with water and crystalline monohydrate are studied. Depending on the object, periodic and non-periodic DFT calculations are used. Particular attention is paid to the metric parameters and enthalpies of intermolecular hydrogen bonds. The identification of noncovalent interactions is carried out by means of the Bader analysis of periodic or non-periodic electron density. The enthalpy of hydrogen bonds is estimated using the Rosenberg formula (PCCP 2 (2000) 2699). The specific proton donor properties of glycine betaine are due to its ability to form intermolecular C–H∙∙∙O bonds with the oxygen atom of a water molecule or the carboxylate group of a neighboring GB. The enthalpy of these bonds can be significantly greater than 10 kJ/mol. The water molecule that forms a hydrogen bond with the carboxylate group of GB also interacts with its CH groups through lone pairs of electrons. The C–H∙∙∙O bonds contribute up to 40% of the total entropy of the GB–water interaction, which is about 45 kJ/mol. The possibility of identifying C–H∙∙∙O bonds by the proton nuclear magnetic resonance method is discussed. [ABSTRACT FROM AUTHOR]

Intermolecular interactions, in particular hydrogen bonds, play a key role in crystal engineering. The ability to form hydrogen bonds of various types and strengths causes competition between supramolecular synthons in pharmaceutical multicomponent crystals. In this work, we investigate the influence of positional isomerism on the packing arrangements and the network of hydrogen bonds in multicomponent crystals of the drug riluzole with hydroxyl derivatives of salicylic acid. The supramolecular organization of the riluzole salt containing 2,6-dihydroxybenzoic acid differs from that of the solid forms with 2,4- and 2,5-dihydroxybenzoic acids. Because the second OH group is not at position 6 in the latter crystals, intermolecular charge-assisted hydrogen bonds are formed. According to periodic DFT calculations, the enthalpy of these H-bonds exceeds 30 kJ·mol−1. The positional isomerism appears to have little effect on the enthalpy of the primary supramolecular synthon (65–70 kJ·mol−1), but it does result in the formation of a two-dimensional network of hydrogen bonds and an increase in the overall lattice energy. According to the results of the present study, 2,6-dihydroxybenzoic acid can be treated as a promising counterion for the design of pharmaceutical multicomponent crystals. [ABSTRACT FROM AUTHOR]

The effect of the local structure on the 31P NMR chemical shift tensor (CST) has been studied experimentally and simulated theoretically using the density functional theory gauge-independent-atomic-orbital approach. It has been shown that the dominating impact comes from a small number of noncovalent interactions between the phosphorus-containing group under question and the atoms of adjacent molecules. These interactions can be unambiguously identified using the Bader analysis of the electronic density. A robust and computationally effective approach designed to attribute a given experimental 31P CST to a certain local morphology has been elaborated. This approach can be useful in studies of surfaces, complex molecular systems, and amorphous materials. [ABSTRACT FROM AUTHOR]

Charge transport in crystalline organic semiconductors (OSCs) is considerably hindered by low-frequency vibrations introducing dynamic disorder in the charge transfer integrals. Recently, we have shown that the contributions of various vibrational modes to the dynamic disorder correlate with their Raman intensities and suggested a Raman-based approach for estimation of the dynamic disorder and search for potentially high-mobility OSCs. In the present paper, we showcase this approach by revealing the highest-mobility OSC(s) in two series of crystalline naphthalene diimide derivatives bearing alkyl or cycloalkyl substituents. In contrast to our previous studies, Raman spectra are not measured, but are instead calculated using periodic DFT. As a result, an OSC with a potentially high charge mobility is revealed in each of the two series, and further mobility calculations corroborate this choice. Namely, for the naphthalene diimide derivatives with butyl and cyclopentyl substituents, the estimated room-temperature isotropic electron mobilities are as high as 6 and 15 cm2 V–1 s–1, respectively, in the latter case even exceeding 20 cm2 V–1 s–1 in a two-dimensional plane. Thus, our results highlight the potential of using the calculated Raman spectra to search for high-mobility crystalline OSCs and reveal two promising OSCs, which were previously overlooked. [ABSTRACT FROM AUTHOR]

Energy/enthalpy of intermolecular hydrogen bonds (H-bonds) in crystals have been calculated in many papers. Most of the theoretical works used non-periodic models. Their applicability for describing intermolecular H-bonds in solids is not obvious since the crystal environment can strongly change H-bond geometry and energy in comparison with non-periodic models. Periodic DFT computations provide a reasonable description of a number of relevant properties of molecular crystals. However, these methods are quite cumbersome and time-consuming compared to non-periodic calculations. Here, we present a fast quantum approach for estimating the energy/enthalpy of intermolecular H-bonds in crystals. It has been tested on a family of crystalline peroxosolvates in which the H∙∙∙O bond set fills evenly (i.e., without significant gaps) the range of H∙∙∙O distances from ~1.5 to ~2.1 Å typical for strong, moderate, and weak H-bonds. Four of these two-component crystals (peroxosolvates of macrocyclic ethers and creatine) were obtained and structurally characterized for the first time. A critical comparison of the approaches for estimating the energy of intermolecular H-bonds in organic crystals is carried out, and various sources of errors are clarified. [ABSTRACT FROM AUTHOR]

The study of the formation of microstructures during the interaction of a protonated drug-like compound (API) with a maleic acid monoanion sheds light on the assembly processes in an aqueous solution at the molecular level. Molecular dynamics (MD) simulations coupled with density functional theory (DFT) calculations made it possible to find initial hydrogen bonding motifs during the assembly process, leading to the formation of heterodimers and trimers. The process of trimer formation [protonated API—maleic acid monoanion—protonated API] proceeds through the formation of three intermolecular H-bonds by the CO2− group of the maleic acid monoanion in both systems. The total enthalpy/energy of these H-bonds is more than 70 kJ/mol. Thus, the maleic acid monoanion plays a key role in the processes of association in aqueous solution, and the interaction of the maleic acid monoanion with API is more preferable than the interaction of API molecules with each other. DFT computations in the discrete continuum approximation reveal the spectral features of heterodimers and trimers, and the ATR-IR spectra confirmed these findings. MD simulations followed by DFT calculations made it possible to describe the initial stages of the formation of pharmaceutical cocrystals in an aqueous solution. [ABSTRACT FROM AUTHOR]

Self-assembly of organic ions in aqueous solutions is a hot topic at the present time, and substances that are well-soluble in water are usually studied. In this work, aqueous solutions of sodium diclofenac are investigated, which, like most medicinal compounds, is poorly soluble in water. Classical MD modeling of an aqueous solution of diclofenac sodium showed equilibrium between the hydrated anion and the hydrated dimer of the diclofenac anion. The assignment and interpretation of the bands in the UV, NIR, and IR spectra are based on DFT calculations in the discrete-continuum approximation. It has been shown that the combined use of spectroscopic methods in various frequency ranges with classical MD simulations and DFT calculations provides valuable information on the association processes of medical compounds in aqueous solutions. Additionally, such a combined application of experimental and calculation methods allowed us to put forward a hypothesis about the mechanism of the effect of diclofenac sodium in high dilutions on a solution of diclofenac sodium. [ABSTRACT FROM AUTHOR]

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.

Further progress in organic electronics demands new highly efficient organic semiconductor (OS) materials. So far, however, band‐like charge transport with high mobilities has been reliably demonstrated only in a few OSs, and development of efficient methods for search of high‐mobility materials among a plethora of OSs remains extremely important. In the present work, a spectroscopic method is presented for screening of crystalline OSs with efficient charge transport, to be used prior to time‐consuming device measurements. Specifically, the work focuses on a physical rationale and an experimental benchmark of a correlation between the intensities of the low‐frequency Raman spectrum and the strength of dynamic disorder limiting the charge‐carrier mobility in a material. As a result, two physics‐inspired spectroscopic descriptors for charge‐carrier mobility estimation are suggested, both of which clearly correlate with device mobilities reported for various crystalline OSs. It is anticipated that the spectroscopic method based on these descriptors can serve as a powerful search tool for revealing new high‐mobility OS materials. [ABSTRACT FROM AUTHOR]

Efficient operation of organic electronic devices requires high charge‐carrier mobilities in their active layers, but only several organic semiconductors show confirmed charge‐carrier mobilities exceeding that of amorphous silicon (≈1 cm2 V−1 s−1). Charge transport in high‐mobility organic semiconductor crystals is considerably hindered by non‐local electron‐phonon interaction (NLEPI) transforming dynamic disorder induced by low‐frequency (LF) vibrations into fluctuations of charge transfer integrals. In this work, using two crystals of naphthalene diimide derivatives as an example, LF vibrational modes that strongly modulate the charge transfer integrals are computationally revealed. The importance of the discussed LF modes for limiting the charge‐carrier mobility is justified by analyzing the effect of the dynamic disorder on the charge‐carrier dynamics, estimating the charge‐carrier mobility in the two crystals, and observing quite a good agreement of the latter with the experimental values. Finally, it is shown that the contribution of various modes to the NLEPI correlates with their experimental Raman intensities. As a result, it is suggested that LF Raman spectroscopy can be used for experimental study of NLEPI, which can help with screening organic semiconductors showing high charge‐carrier mobility and promote rational design of such materials. [ABSTRACT FROM AUTHOR]

2-Aminobenzimidazole hemiperoxosolvate 2(C7H7N3)·H2O2 was synthesized and studied by single crystal X-ray analysis and periodic (solid-state) DFT calculations. The obtained compound, after urea and melamine peroxosolvates, is the third example of an H2O2 crystalline adduct stabilized with the maximum possible number of hydrogen bonds formed by one hydrogen peroxide molecule – 2 H-bonds as proton donors and 4 as acceptors. Due to the small size of the hydrogen peroxide molecule, its hydrogen bonding energy contributes the maximal impact and determines the relative value of the hydrogen bonding energy of the peroxosolvate crystal and can be suggested as an energetic criterion of perhydrate stability. The total energy of the 6 hydrogen bonds formed by one hydrogen peroxide molecule in all three compounds (∼140–∼170 kJ mol−1) was calculated and compared to the corresponding values for crystalline hydrogen peroxide and L -serine peroxosolvate. The total energy of the 4 hydrogen bonds of hydrogen peroxide molecule in crystalline H2O2 and L -serine peroxosolvate (150 and 113 kJ mol−1, respectively) was evaluated by solid-state DFT calculations. [ABSTRACT FROM AUTHOR]

The crystal structure of NH4+OOH- is determined from single-crystal x-ray data obtained at 150 K. The crystal belongs to the space group P21/c and has four molecules in a unit cell. The structure consists of discrete NH4+ and OOH- ions. The OOH- ions are linked by short hydrogen bonds (2.533 Å) to form parallel infinite chains. The ammonium ions form links between these chains (the N...O distances vary from 2.714 to 2.855 Å) giving a three-dimensional network. The harmonic IR spectrum and H-bond energies are computed at the Perdew-Burke-Ernzerhof (PBE)/6-31G** level with periodic boundary conditions. A detailed analysis of the shared (bridging) protons' dynamics is obtained from the CPMD simulations at different temperatures. PBE functional with plane-wave basis set (110 Ry) is used. At 10 K the shared proton sits near the oxygen atom, only a few proton jumps along the chain are detected at 70 K while at 270 K numerous proton jumps exist in the trajectory. The local-minimum structure of the space group Cc is localized. It appears as a result of proton transfer along a chain. This process is endothermic (∼2 kJ/mol) and is described as P21/c↔2Cc. The computed IR spectrum at 10 K is close to the harmonic one, the numerous bands appear at 70 K while at 270 K it shows a very broad absorption band that covers frequencies from about 1000 to 3000 cm-1. The advantages of the NH4+OOH- crystal as a promising model for the experimental and DFT based molecular dynamics simulation studies of proton transfer along the chain are discussed. [ABSTRACT FROM AUTHOR]

Herein, peroxosolvates of the cyclic dipeptides disarcosine (C6H10N2O2·H2O2), dialanine (C6H10N2O2·2(H2O2)), diglycine (C4H6N2O2·2(H2O2) and C4H6N2O2·1.786(H2O2)·0.214(H2O)) were synthesized and studied by single crystal X-ray analysis and periodic DFT calculations. The hydrogen bonding networks of cyclic diglycine peroxosolvate and isomorphous hydrate were characterized using Bader analysis of periodic electron density and empirical correlations between enthalpy and metric and spectroscopic parameters of the H-bond. The obtained data for the peroxosolvate of cyclic dipeptides provided a molecular-level insight into the non-redox interaction of hydrogen peroxide with the peptide backbone in aqueous systems. In all structures, H2O2 acts as a proton donor in two hydrogen bonds. The carbonyl oxygen atom of the peptide (–CO–NH–) forms a relatively stronger hydrogen bond with the hydrogen peroxide molecule (32–34 kJ mol−1) as compared to that with water in the isomorphous hydrate of cyclic diglycine (26–28 kJ mol−1). The hydrogen atom of the peptide group (–CO–NH–) can form a moderate H-bond with hydrogen peroxide (25 kJ mol−1). The total hydrogen bonding energy of the peroxosolvate is higher than that of the corresponding hydrate (91 vs. 82 kJ mol−1). The stronger hydrogen bonding in peroxosolvates as compared to that in the hydrate and the fact that the intermolecular H-bonds C(＝O)NH⋯O＝CNH between cyclic dipeptides are not found in peroxosolvates, despite being prevalent in the structure of nonsolvated dipeptides, imply that hydrogen peroxide can interfere with the secondary structure of proteins via a mechanism that can lead to reversible inhibition or signaling in living systems. [ABSTRACT FROM AUTHOR]

New zwitterionic cocrystals of fenamate drugs and diclofenac with the naturally occurring amino acid l-proline have been obtained and thoroughly characterised by a variety of experimental and theoretical techniques. A crystal structure analysis and a CSD survey allowed us to establish a distinct supramolecular motif formed by the double chain arrangement of proline entities, which was found to play the structure-directing role in the proline zwitterionic cocrystals. Special graph set notation has been introduced to describe the particular type of the bifurcated H-bond observed in the crystal structures of proline with different APIs. Solid state DFT calculations enabled us to quantify different intermolecular interactions in the new cocrystals obtained, to interpret specific features of supramolecular organisation, and to explain the reasons for selective cocrystallisation of l-proline with fenamates. Cocrystallisation of the diclofenac and fenamate APIs with l-proline improved the solubility of these drugs in comparison with the parent drugs. The cocrystal solubility advantage values determined from eutectic concentrations at pH 6.8 and 25.0 °C were found to be in the range from 9 to 25. [ABSTRACT FROM AUTHOR]

The discovery of novel explosophoric building blocks for the construction of energetic compounds is extremely rare. Here, based on the comparative experimental properties and computational analysis of compounds where nitroaryl backbones were bonded with various nitrogen/oxygen-rich groups, it is shown that compounds having the azasydnone group possess higher density, detonation performance and thermal stability than their corresponding nitro, azido and tetrazole-analogs. All of these properties, as well as the oxygen balanced content of the "green" nitrogen rich endothermic unit make them an attractive explosophoric building block in the field of energetic materials chemistry. [ABSTRACT FROM AUTHOR]

Two variants of density functional theory computations have been applied to characterization of hydrogen bonds of the 1-(2-hydroxylethyl)-3-methylimidazolium acetate ([C 2 OHmim][OAc]), i.e. with and without inclusion of dispersion interactions. A comparison of the results demonstrates that London dispersion interactions have very little impact on the energetical, geometrical, infrared spectroscopic and electron density parameters of charge-assisted intermolecular hydrogen bonds functioning both in the crystal of the [C 2 OHmim][OAc] and in the isolated [C 2 OHmim] + [OAc] − ion pairs. [ABSTRACT FROM AUTHOR]

The Cambridge Structural Database has been used to investigate the detailed environment of H2O2 molecules and hydrogen-bond patterns within "true" peroxosolvates in which the H2O2 molecules do not interact directly with the metal atoms. A study of 65 crystal structures and over 260 hydrogen bonds reveals that H2O2 always forms two H-bonds as proton donors and up to four H-bonds as a proton acceptor, but the latter can be absent altogether. The necessary features of peroxosolvate coformers are clarified. (1) Coformers should not participate in redox reactions with H2O2 and should not catalyze its decomposition. (2) Coformers should be Brønsted bases or exhibit amphoteric properties. The efficiency of the proposed criteria for peroxosolvate formation is illustrated by the synthesis and characterization of several new crystals. Conditions preventing the H2O2/H2O isomorphous substitution are essential for peroxosolvate stability: (1) Every H2O2 in the peroxosolvate has to participate in five or six hydrogen bonds. (2) The distance between the two proton acceptors forming H-bonds with the H2O2 molecule should be longer than the distance defined by the nature of the acceptor atoms. A study of 65 crystal structures and over 260 hydrogen bonds reveals that H2O2 always forms two H-bonds as proton donors and up to four H-bonds as a proton acceptor, but the latter can be absent altogether. [ABSTRACT FROM AUTHOR]

Intrinsic solubility of the isoniazid-carboxylic acid cocrystals is explored using thermodynamic cycle of transferring from crystal to gas and then to solution. The enthalpy/Gibbs free energy of phase transitions is computed by solid-state DFT (crystal) and DFT methods with/without accounting for polar solvent (aqueous solution/gas). The dissolution process of the isoniazid-dicarboxylic acid 2:1 cocrystals is found to be enthalpy-determined. The linear correlation between the theoretical sublimation enthalpies and experimental Gibbs energy of solution is established. According to it, the increase of stability causes the decrease of the considered cocrystals solubility. We conclude that a soluble and relatively stable cocrystal of isoniazid should be characterized by the sublimation enthalpy varying from 185 to 200 kJ·mol −1 . Bader analysis of theoretical periodic electron density enables us to quantify the non-covalent interactions and clarify their role in formation of the isoniazid cocrystals. The sublimation enthalpy of the cocrystals is defined by the structure of the coformer molecule. Its value is less 150 kJ·mol −1 in the case of aromatic acids and larger than 180 kJ·mol −1 for the aliphatic dicarboxylic acids. The sublimation enthalpy increases with the increase of the dicarboxylic acid hydrocarbon chain. [ABSTRACT FROM AUTHOR]

The lattice energy Elattof the two-componentcrystals (three co-crystals, a salt, and a hydrate) is evaluated usingtwo schemes. The first one is based on the total energy of the crystaland its components computed using the solid-state density functionaltheory method with the plane-wave basis set. The second approach exploresintermolecular energies estimated using the bond critical point parametersobtained from the Bader analysis of crystalline electron density orthe pairwise potentials. The Elattvaluesof two-component crystals are found to be lower or equal to the sumof the absolute sublimation enthalpies of the pure components. Thecomputed energies of the supramolecular synthons vary from ∼80to ∼30 kJ/mol and decrease in the following order: acid–amide> acid–pyridine > hydroxyl–acid > amide–amide> hydroxyl–pyridine. The contributions from different typesof noncovalent interactions to the Elattvalue are analyzed. We found that at least 50% of the lattice energycomes from the heterosynthon and a few relatively strong H-bonds betweenthe heterodimer and the adjacent molecules. [ABSTRACT FROM AUTHOR]

The infrared (IR) spectra of waterâ€'ethanol (EtOH) solutions of HCl are measured over a wide range of acid concentration at fixed H2O―EtOH ratios (1 : 1, 1 : 2, and 1 : 40). In these systems, different proton disolvates with (quasi)symmetrical Hâ€bonds are formed. Their structure and vibrational features are revealed by the density functional theory method coupled with the polarizable continuum model of solvation. In dilute acidic solutions, the Zundelâ€type H5O2+ ion is mainly formed. In concentrated HCl solutions, the ions (H2O···H···O(H)Et)+ and (Et(H)O···H···O(H)Et)+ with the quasiâ€symmetrical O···H+···O unit having O···O separation <2.45 â'« appear. The first ion characterized by the IRâ€intensive band around 1800 cmâˆ'1 is mainly formed in the 1 : 1 waterâ€'ethanol systems. The second ion exists in the 1 : 2 and 1 : 40 waterâ€'ethanol systems. Its spectroscopic signatures are the groups of the IRâ€intensive bands around 800 and 1050 cmâˆ'1. In highly concentrated HCl solutions with the 1 : 40 waterâ€'ethanol ratio, a neutral Et(H)O···H+···Clâˆ' complex exists. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Nitranilic acid (2,5-dihydroxy-3,6-dinitro-2,5-cyclohexadiene-1,4-dione) as a strong dibasic acid in acidic aqueous media creates the Zundel cation, H5O2+. The structural unit in a crystal comprises (H5O2)2+ (2,5-dihydroxy-3,6-dinitro-1,4-benzoquinonate)2− dihydrate where the Zundel cation reveals no symmetry, being an ideal case for studying proton dynamics and its stability. The Zundel cation and proton transfer dynamics are studied by variable-temperature X-ray diffraction, IR and solid-state NMR spectroscopy, and various quantum chemical methods, including periodic DFT calculations, ab initio molecular dynamics simulation, and quantization of nuclear motion along three fully coupled internal coordinates. The Zundel cation features a short H-bond with the O…O distance of 2.433(2) Å with an asymmetric placement of hydrogen. The proton potential is of a single well type and, due to the non-symmetric surroundings, of asymmetric shape. The formation of the Zundel cation is facilitated by the electronegative NO2 groups. The employed spectroscopic techniques supported by calculations confirm the presence of a short H-bond with a complex proton dynamics. [ABSTRACT FROM AUTHOR]

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]

The ortho-hydroxy aryl Schiff base 2-[(E)-(phenylimino)methyl]phenol and its deutero-derivative have been studied by the inelastic incoherent neutron scattering (IINS), infrared (IR) and Raman experimental methods, as well as by Density Functional Theory (DFT) and Density-Functional Perturbation Theory (DFPT) simulations. The assignments of vibrational modes within the 3500–50 cm−1 spectral region made it possible to state that the strong hydrogen bond in the studied compound can be classified as the so-called quasi-aromatic bond. The isotopic substitution supplemented by the results of DFT calculations allowed us to identify vibrational bands associated with all five major hydrogen bond vibrations. Quasi-isostructural polymorphism of 2-[(E)-(phenylimino)methyl]phenol (SA) and 2-[(E)-(phenyl-D5-imino)methyl]phenol (SA-C6D5) has been studied by powder X-ray diffraction in the 20–320 K temperature range. [ABSTRACT FROM AUTHOR]

Two new hydrated multicomponent crystals of zwitterionic 2-aminonicotinic acid with maleic and fumaric acids have been obtained and thoroughly characterized by a variety of experimental (X-ray analysis and terahertz Raman spectroscopy) and theoretical periodic density functional theory calculations, followed by Bader analysis of the crystalline electron density) techniques. It has been found that the Raman-active band in the region of 300 cm−1 is due to the vibrations of the intramolecular O-H...O bond in the maleate anion. The energy/enthalpy of the intermolecular hydrogen bonds was estimated by several empirical approaches. An analysis of the interaction networks reflects the structure-directing role of the water molecule in the examined multicomponent crystals. A general scheme has been proposed to explain the proton transfer between the components during the formation of multicomponent crystals in water. Water molecules were found to play the key role in this process, forming a "water wire" between the COOH group of the dicarboxylic acid and the COO– group of the zwitterion and the rendering crystal lattice of the considered multicomponent 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]

Synthesis of multicomponent solid forms is an important method of modifying and fine-tuning the most critical physicochemical properties of drug compounds. The design of new multicomponent pharmaceutical materials requires reliable information about the supramolecular arrangement of molecules and detailed description of the intermolecular interactions in the crystal structure. It implies the use of a combination of different experimental and theoretical investigation methods. Organic salts present new challenges for those who develop theoretical approaches describing the structure, spectral properties, and lattice energy Elatt. These crystals consist of closed-shell organic ions interacting through relatively strong hydrogen bonds, which leads to Elatt > 200 kJ/mol. Some technical problems that a user of periodic (solid-state) density functional theory (DFT) programs encounters when calculating the properties of these crystals still remain unsolved, for example, the influence of cell parameter optimization on the Elatt value, wave numbers, relative intensity of Raman-active vibrations in the low-frequency region, etc. In this work, various properties of a new two-component carbendazim maleate crystal were experimentally investigated, and the applicability of different DFT functionals and empirical Grimme corrections to the description of the obtained structural and spectroscopic properties was tested. Based on this, practical recommendations were developed for further theoretical studies of multicomponent organic pharmaceutical crystals. [ABSTRACT FROM AUTHOR]

Second order Mo\ller-Plesset perturbation theory and density functional theory are employed to localize several stationary points on the potential energy surface of the cyclic methanol tetramer. Two cyclic isomers are identified: one of S[sub 4] symmetry, with methyl groups in up-down-up-down configuration, and a second one of C[sub i] symmetry, with the methyl groups in up-up-down-down configuration. The latter minimum is 360 cm[sup -1] above the S[sub 4] minimum, with a barrier of 475 cm[sup -1] separating them. These isomers give rise to four asymmetric OH modes around 3300 cm[sup -1]. A model of the concerted proton transfer, S[sub 4]→D[sub 2d]→S[sub 4] (D[sub 2d] is the transition structure), yields an estimate of 0.7 cm[sup -1] for the tunneling splitting of the totally symmetric OH stretch vibrational fundamental. Raman spectra would show evidence of this fundamental and help to identify admixtures of the C[sub i] isomer. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The gas phase IR spectrum of the O...H...O fragment of H[sub 5]O[sub 2][sup +] and its deuterated analogue are calculated using ab initio classical molecular dynamics based on a MP2 potential energy surface. The assignment of the bands is made in terms of the quantum four-dimensional model calculations of anharmonic frequencies and intensities. Comparing low and high kinetic temperature simulations the importance of anharmonicities of the potential energy surface for understanding the vibrational band structure is highlighted. It is shown that any reasonable simulation of IR spectra of systems with very strong hydrogen bonds has to account for the dipole moment function beyond the linear approximation. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The adsorption of a single H2O2 or H2O molecule on a family of periodic slab models of γ‐AlOOH is studied by solid‐state DFT. The single H2O2 or Н2О molecule interacts with the perfect (010) slab by intermolecular hydrogen bonds (H‐bonds). In the models of γ‐AlOOH with oxygen and aluminum vacancies, H2O2 or Н2О also forms covalent O∙∙∙Al bonds. The energies of covalent O∙∙∙Al and H‐bonds are estimated by a combined approach based on simultaneous consideration of the total binding energies with BSSE correction and empirical schemes of the Н‐bond energy evaluation. The O∙∙∙Al bond energy ranges from ~75 to ~156 kJ mol−1. The total energy of H‐bond interactions in the case of H2O2 exceeds that of Н2О by ~30 kJ mol−1 for all considered slab models. In contrast to Н2О, a H2O2 molecule always forms two H‐bonds as the proton donor. The energy of these bonds noticeably increase on defect γ‐AlOOH surfaces in comparison with the perfect slab due to formation of short (strong) H‐bonds by adsorbed H2O2. [ABSTRACT FROM AUTHOR]

The spectrum of guanidinium acetate in aqueous solution has been recorded by attenuated total reflectance infrared spectroscopy (ATR-IR). Assignments of the bands have been done using the polarizable continuum model (PCM). Three IR intensive bands at 1670, 1550, and 1410 cm −1 are associated with stretching and bending vibrations of the groups forming a ring of six heavy atoms of the bidentate configuration of guanidinium acetate. The relatively weak broad band near 2200 cm −1 is tentatively assigned to the stretching vibration of the N H⋯O fragment of the hydrogen-bonded ion pairs. [ABSTRACT FROM AUTHOR]