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1.
Molecules ; 25(10)2020 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-32455564

RESUMO

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.

2.
J Chem Phys ; 150(14): 144706, 2019 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-30981271

RESUMO

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.

3.
ACS Omega ; 3(8): 10317-10330, 2018 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-30198007

RESUMO

The hypercoordinated silicon chlorides ClSi[(o-OC6H4)3N] (3) and ClSi[(OC6H2Me2CH2)3N] (5) were used for the synthesis of catenated derivatives (Me3Si)3SiSi[(o-OC6H4)3N] (9), (Me3Si)3SiSiMe2SiMe2Si(SiMe3)2Si[(o-OC6H4)3N] (11), and (Me3Si)3SiSi[(OC6H2Me2CH2)3N] (13) in reactions with (Me3Si)3SiK·THF (7) or (Me3Si)3SiK·[18-crown-6] (8). It was found that the nature of the (Me3Si)3SiK solvate determines the product of interaction, resulting in the formation of (Me3Si)3Si(CH2)4OSi[(OC6H2Me2CH2)3N] (12) or 13. Compounds obtained were characterized using multinuclear NMR and UV-vis spectroscopy and mass spectrometry. The molecular structures of 3, 9, and 11-13 were investigated by single-crystal X-ray analysis, featuring hypercoordinated Si atoms in a trigonal-bipyramidal coordination environment with O atoms in the equatorial plane. The structure of the side product [N(CH2C6H2Me2O)3Si]2O (6) was also studied, indicating highly tetrahedrally distorted trigonal-bipyramidal environment at the Si atoms, which was confirmed by crystal density functional theory calculations indicating the very weak Si ← N interaction. The Si···N interatomic distances span a broad range (2.23-2.78 Å). The dependence of structural and NMR parameters for hypercoordinated catenated compounds from the type of the ligand was established.

4.
ACS Omega ; 3(1): 302-313, 2018 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-30023777

RESUMO

Diclofenac (active ingredient of Voltaren) has a significant, multifaceted role in medicine, pharmacy, and biochemistry. Its physical properties and impact on biomolecular structures still attract essential scientific interest. However, its interaction with water has not been described yet at the molecular level. In the present study, we shed light on the interaction between the steric hindrance (the intramolecular N-H···O bond, etc.) carboxylate group (-CO2-) with water. Aqueous solution of sodium declofenac is investigated using attenuated total reflection-infrared (ATR-IR) and computational approaches, i.e., classical molecular dynamics (MD) simulations and density functional theory (DFT). Our coupled classical MD simulations, DFT calculations, and ATR-IR spectroscopy results indicated that the -CO2- group of the diclofenac anion undergoes strong specific interactions with the water molecules. The combined experimental and theoretical techniques provide significant insights into the spectroscopic manifestation of these interactions and the structure of the hydration shell of the -CO2- group. Moreover, the developed methodology for the theoretical analysis of the ATR-IR spectrum could serve as a template for the future IR/Raman studies of the strong interaction between the steric hindrance -CO2- group of bioactive molecules with the water molecules in dilute aqueous solutions.

5.
J Phys Chem Lett ; 8(13): 2875-2880, 2017 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-28590744

RESUMO

Organic electronics requires materials with high charge mobility. Despite decades of intensive research, charge transport in high-mobility organic semiconductors has not been well understood. In this Letter, we address the physical mechanism underlying the exceptionally high band-like electron mobility in F2-TCNQ (2,5-difluoro-7,7,8,8-tetracyanoquinodimethane) single crystals among a crystal family of similar compounds Fn-TCNQ (n = 0, 2, 4) using a combined experimental and theoretical approach. While electron transfer integrals and reorganization energies did not show outstanding features for F2-TCNQ, Raman spectroscopy and solid-state DFT indicated that the frequency of the lowest vibrational mode is nearly twice higher in the F2-TCNQ crystal than in TCNQ and F4-TCNQ. This phenomenon is explained by the specific packing motif of F2-TCNQ with only one molecule per primitive cell so that electron-phonon interaction decreases and the electron mobility increases. We anticipate that our findings will encourage investigators for the search and design of organic semiconductors with one molecule per primitive cell and/or the poor low-frequency vibrational spectrum.

6.
J Phys Chem Lett ; 6(21): 4431-6, 2015 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-26496074

RESUMO

Charge-assisted hydrogen bonds (CAHBs) play critical roles in many systems from biology through to materials. In none of these areas has the role and function of CAHBs been explored satisfactorily because of the lack of data on the energy of CAHBs in the condensed phases. We have, for the first time, quantified three types of CAHBs in both the condensed and gas phases for 1-(2'-hydroxylethyl)-3-methylimidazolium acetate ([C2OHmim][OAc]). The energy of conventional OH···[OAc](-) CAHBs is ∼10 kcal·mol(-1), whereas nonconventional C(sp2)H···[OAc](-) and C(sp3)H···[OAc](-) CAHBs are weaker by ∼5-7 kcal·mol(-1). In the gas phase, the strength of the nonconventional CAHBs is doubled, whereas the conventional CAHBs are strengthened by <20%. The influence of cooperativity effects on the ability of the [OAc](-) anion to deprotonate the imidazolium cation is evaluated. The ability to quantify CAHBs in the condensed phase on the basis of easier accessible gas-phase estimates is highlighted.

7.
J Phys Chem B ; 119(33): 10466-77, 2015 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-26258951

RESUMO

Cocrystal screening of 4-hydroxybenzamide with a number of salicylates (salicylic acid, SA; 4-aminosalicylic acid, PASA; acetylsalicylic acid, ASA; and salicylsalicylic acid, SSA) was conducted to confirm the formation of two cocrystals, [SA+4-OHBZA] (1:1) and [PASA+4-OHBZA] (1:1). Their structures were determined using single-crystal X-ray diffraction, and the hydrogen-bond network topology was studied. Thermodynamic characteristics of salicylic acid cocrystal sublimation were obtained experimentally. It was proved that PASA cocrystallization with 4-OHBZA makes the drug more stable and prevents the irreversible process of decarboxylation of PASA resulting in formation of toxic 3-aminophenol. The pattern of non-covalent interactions in the cocrystals is described quantitatively using solid-state density functional theory followed by Bader analysis of the periodic electron density. It has been found that the total energy of secondary interactions between synthon atoms and the side hydroxyl group of the acid molecule in [SA+4-OHBZA] (1:1) and [PASA+4-OHBZA] (1:1) cocrystals is comparable to the energy of the primary acid-amide heterosynthon. The theoretical value of the sublimation enthalpy of [SA+4-OHBZA], 231 kJ/mol, agrees fairly well with the experimental one, 272 kJ/mol. The dissolution experiments with [SA+4-OHBZA] have proved that the relatively large cocrystal stability in relation to the stability of its components has a negative effect on the dissolution rate and equilibrium solubility. The [PASA+4-OHBZA] (1:1) cocrystal showed an enhancement of apparent solubility compared to that of the corresponding pure active pharmaceutical ingredient, while their intrinsic dissolution rates are comparable.


Assuntos
Benzamidas/química , Transição de Fase , Teoria Quântica , Salicilatos/química , Cristalografia por Raios X , Ligação de Hidrogênio , Modelos Moleculares , Conformação Molecular , Solubilidade , Termodinâmica
8.
Inorg Chem ; 54(16): 8058-65, 2015 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-26241061

RESUMO

Potassium (K6[Ge6(µ-OO)6(µ-O)6(OH)6]·14H2O, 1), cesium ammonium (Cs4.2(NH4)1.8[Ge6(µ-OO)6(µ-O)6(OH)6]·8H2O, 2), and potassium ammonium (K2.4(NH4)3.6[Ge6(µ-OO)6(µ-O)6(OH)6]·6H2O, 3) peroxogermanates were isolated from 3% hydrogen peroxide aqueous solutions of the corresponding hydroxogermanates and characterized by single crystal and powder X-ray diffraction studies and by Raman spectroscopy and thermal analysis. The crystal structure of all three compounds consists of cations of potassium and/or ammonium and cesium, water molecules, and centrosymmetric hexanuclear peroxogermanate anion [Ge6(µ-OO)6(µ-O)6(OH)6](6-) with six µ-oxo- and six µ-peroxo groups. Peroxogermanates demonstrate relatively high thermal stability: the peroxide remains in the structure even after water release after heating to 100-120 °C. DFT calculations of the peroxogermanate [Ge6(µ-OO)6(µ-O)6(OH)6](6-) anion confirm its higher thermodynamic stability compared to the hydroperoxo- and oxogermanate analogues.

9.
J Phys Chem B ; 118(24): 6803-14, 2014 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-24861612

RESUMO

A new cocrystal of 2-hydroxybenzamide (A) with 4-acetamidobenzoic acid (B) has been obtained by the DSC screening method. Thermophysical analysis of the aggregate [A:B] has been conducted and a fusion diagram has been plotted. Cocrystal formation from melts was studied by using thermomicroscopy. A cocrystal single-crystal was grown and its crystal structure was determined. The pattern of noncovalent interactions has been quantified using the solid-state DFT computations coupled with the Bader analysis of the periodic electron density. The sublimation processes of A-B cocrystal have been studied and its thermodynamic functions have been calculated. The classical method of substance transfer by inert gas-carrier was chosen to investigate sublimation processes experimentally. The lattice energy is found to be 143 ± 4 kJ/mol. It is lower than the sum of the corresponding values of the cocrystal pure components. The theoretical value of the lattice energy, 156 kJ/mol, is in reasonable agreement with the experimental one. A ternary phase diagram of solubility (A-B-ethanol) has been plotted and the areas with solutions for growing thermodynamically stable cocrystals have been determined.


Assuntos
Salicilamidas/química , Benzamidas/química , Varredura Diferencial de Calorimetria , Cristalografia por Raios X , Gases/química , Conformação Molecular , Solubilidade , Temperatura , Termodinâmica , para-Aminobenzoatos/química
10.
Phys Chem Chem Phys ; 16(3): 998-1007, 2014 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-24281720

RESUMO

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.


Assuntos
Cicloexenos/química , Nitrocompostos/química , Teoria Quântica , Termodinâmica , Cátions/química , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Espectrofotometria Infravermelho , Difração de Raios X
11.
J Phys Chem A ; 117(35): 8459-67, 2013 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-23924151

RESUMO

The structure, IR harmonic frequencies and intensities of normal vibrations of 20 molecular crystals with the X-Cl···Cl-X contacts of different types, where X = C, Cl, and F and the Cl···Cl distance varying from ~3.0 to ~4.0 Å, are computed using the solid-state DFT method. The obtained crystalline wave functions have been further used to define and describe quantitatively the Cl···Cl interactions via the electron-density features at the Cl···Cl bond critical points. We found that the electron-density at the bond critical point is almost independent of the particular type of the contact or hybridization of the ipso carbon atom. The energy of Cl···Cl interactions, E(int), is evaluated from the linking E(int) and local electronic kinetic energy density at the Cl···Cl bond critical points. E(int) varies from 2 to 12 kJ/mol. The applicability of the geometrical criterion for the detection of the Cl···Cl interactions in crystals with two or more intermolecular Cl···Cl contacts for the unique chlorine atom is not straightforward. The detection of these interactions in such crystals may be done by the quantum-topological analysis of the periodic electron density.


Assuntos
Cloro/química , Termodinâmica , 3,3'-Diclorobenzidina/química , Simulação por Computador , Conformação Molecular
12.
J Phys Chem B ; 117(30): 9094-105, 2013 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-23822750

RESUMO

Hydrogen bonding in ionic liquids based on the 1-(2'-hydroxylethyl)-3-methylimidazolium cation ([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 a range of spectroscopic and computational techniques and, in the case of [C2OHmim][PF6], by single crystal X-ray diffraction. The first quantitative estimates of the energy (E(HB)) and the enthalpy (-ΔH(HB)) of H-bonds in bulk ILs were obtained from a theoretical analysis of the solid-state electron-density map of crystalline [C2OHmim][PF6] and an analysis of the IR spectra in crystal and liquid samples. E(HB) for OH···[PF6](-) H-bonds amounts to ~3.4-3.8 kcal·mol(-1), whereas weaker H-bonds (2.8-3.1 kcal·mol(-1)) are formed between aromatic C2H group 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(-1)l) < [TFA] (6.2 kcal·mol(-1)). The formation of aggregates of self-associated [C2OHmim](+) cations is present in liquid [C2OHmim][PF6], [C2OHmim][BF4], and [C2OHmim][Tf2N], with the energy of the OH···OH H-bonds amounting to ~6 kcal·mol(-1). Multiple secondary interactions in the bulk ILs influence their structure, vibrational spectra, and H-bond strength. In particular, these interactions can blue-shift the stretching frequencies of the CH groups of the imidazolium ring in spite of red-shifting CH···[A](-) H-bonds. They also weaken the H-bonding in the IL relative to the isolated ion pairs, with these anticooperative effects amounting to ca. 50% of the E(HB) value.

13.
J Phys Chem A ; 115(46): 13657-63, 2011 Nov 24.
Artigo em Inglês | MEDLINE | ID: mdl-22004006

RESUMO

The structure, IR spectrum, and H-bond network in the serine-H(2)O and serine-H(2)O(2) 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-H(2)O and serine-H(2)O(2). 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 H(2)O and a combination vibration of the symmetric and asymmetric bendings of H(2)O(2). 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 H(2)O/H(2)O(2) substitution does not change the H-bond network; however, the energy of the amino acid-H(2)O(2) contacts increases up to 60 kJ/mol. This is caused by the fact that H(2)O(2) is a much better proton donor than H(2)O in the title crystals.


Assuntos
Aminoácidos/química , Peróxido de Hidrogênio/química , Teoria Quântica , Serina/química , Água/química , Cristalização , Ligação de Hidrogênio
14.
Acta Chim Slov ; 58(3): 402-10, 2011 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-24062098

RESUMO

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.

15.
J Chem Phys ; 133(16): 164506, 2010 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-21033804

RESUMO

The crystal structure of NH(4)(+)OOH(-) is determined from single-crystal x-ray data obtained at 150 K. The crystal belongs to the space group P2(1)/c and has four molecules in a unit cell. The structure consists of discrete NH(4)(+) 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 P2(1)/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 NH(4)(+)OOH(-) crystal as a promising model for the experimental and DFT based molecular dynamics simulation studies of proton transfer along the chain are discussed.

16.
J Phys Chem A ; 114(6): 2393-9, 2010 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-20104882

RESUMO

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.


Assuntos
Ácido Benzoico/química , Simulação por Computador , Fenóis/química , Prótons , Piridinas/química , Ligação de Hidrogênio , Solventes/química , Vibração
17.
Phys Chem Chem Phys ; 11(11): 1702-12, 2009 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-19290341

RESUMO

Proton forms of zeolite chabazite (H-SSZ-13) loaded with 1 to 4 water molecules per acid site are examined by density functional theory with periodic boundary conditions. Equilibrium structures are determined by localizing minima on the potential energy surface and harmonic vibrational frequencies are calculated. Average structures, proton dynamics and anharmonic spectra at finite temperature (350 K) are determined by molecular dynamics (MD). The protonation state is found to depend on the number of water molecules per acid site (loading) following the trend of increasing proton affinity with increasing cluster size. Single water molecules are not protonated, the protonated water dimer is the most stable equilibrium structure with the PBE functional, but not with BLYP. MD shows that even with PBE, the protonated water dimer is not stable at finite temperature. The protonated water trimer may be formed as a short-lived species, but the protonated water tetramer is the smallest stable protonated cluster. For the same global loading (2 : 1), a heterogeneous distribution of adsorbed water molecules over the cells is more stable than a homogeneous one (1 : 1/3 : 1 vs. 2 : 1/2 : 1 for a double cell), i.e. non-protonated and protonated water clusters may exist simultaneously in polyhydrated H-SSZ13. Adsorption energies (0 K) per water molecule decrease from 71 to 51 kJ mol(-1) for n = 1 to n = 4.

18.
J Phys Chem A ; 112(51): 13628-32, 2008 Dec 25.
Artigo em Inglês | MEDLINE | ID: mdl-19053812

RESUMO

The structure, harmonic frequencies, and infrared intensities of the fundamental transitions of potassium hydrogen/deuterium maleate crystals have been computed by the density functional theory with periodic boundary conditions. Different functionals with all-electron Gaussian-type orbital (GTO) basis set have been used. It was found that BLYP/GTO approximation provides the best results for the structural parameters of the KH maleate crystal. Within this approximation, the hydrogen-bonded potential in the KH maleate crystal is extremely shallow. Delocalization of the bridging protons complicates a strict definition of the space group of the crystal; the space groups Pbcm and Pbc2(1) represent an equivalent choice. The periodic BLYP/GTO study provides detailed information on the nature of the internal vibrations of the hydrogen maleate anion, which are located in the range 300-1800 cm(-1). Assignment of the vibrational bands in this frequency region has been performed. The two most intensive bands in the infrared spectrum (approximately 500 and approximately 1450 cm(-1)) are caused by the "pure" asymmetric O...H...O stretching vibrations and the stretching motion of the bridging proton heavily mixed with the C-C stretching and CH bending vibrations, respectively. A crystalline environment is found to play an important role in the low-frequency region and is negligible above 1000 cm(-1). The H/D substitution slightly changes the vibration frequencies, involving the stretching motion of the bridging proton because of the strong coupling between this motion and the various internal vibrations of the hydrogen maleate anion.

19.
Phys Chem Chem Phys ; 7(2): 258-63, 2005 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-19785146

RESUMO

The structure as well as IR and inelastic neutron scattering (INS) spectra of H5O2+ in crystalline H5O2+ClO4- were simulated using Car-Parrinello molecular dynamics with the BLYP functional. The potential of the O...H+...O fragment is very shallow. The Pnma structure, assumed in the X-ray study to be the most suitable choice, is a saddle point on the potential energy surface, while the P2(1)2(1)2(1) minimum structure is only 20 cm(-1) lower in energy. The computed INS and IR spectra enable us to achieve a complete assignment of the observed spectra. The broad band between 1000 and 1400 cm(-1) is due to the asymmetric stretch and one of the bending vibrations of the O...H+...O fragment, while the band between 1600 and 1800 cm(-1) is due to the bending vibration of the water molecules and the second bending of the O...H+...O fragment. Comparison with the vibrational spectra of isolated H5O2+, obtained using Born-Oppenheimer molecular dynamics simulation, reveals environmental effects on vibrational proton dynamics in strong H-bonded species. The most pronounced changes are found for the O...H+...O bending modes because the two bending coordinates become distinctly different for the structure that the H5O2+ ion assumes in the crystal.


Assuntos
Modelos Químicos , Percloratos/química , Água/química , Cristalografia , Ligação de Hidrogênio , Nêutrons , Prótons , Espalhamento a Baixo Ângulo , Espectrofotometria Infravermelho
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