Experimental and computational study of HXeY...HX complexes (X, Y = Cl and Br): an example of exceptionally large complexation effect

The complexes of xenon hydrides HXeY (Y = Cl and Br) with hydrogen halides HX (X = Cl and Br) have been studied both computationally and experimentally in a xenon matrix. The experiments revealed three new complexes: HXeBr...HBr, HXeBr...HCl, and HXeCl...HCl. The experimental assignments were done on the basis of the strong H-Xe stretching absorption of HXeY (Y = Cl and Br) molecules and supported by theoretical results. We experimentally obtained monomer-to-complex blue-shifts of this vibrational mode for all the studied systems (up to approximately 150 cm (-1)). The electronic structure calculations revealed three local structures for each HNgY...HX complexes and their computed interaction energies varied between -460 and -2800 cm (-1). The computational estimates of the vibrational shifts were in agreement with the experimental values. We also found possible experimental absorption belonging to HXeBr...(HBr) 2 trimer and its vibrational shift (+245 cm (-1)) is similar to the computational estimate of a cyclic ternary complex (+252 cm (-1)).     

Blue shifts and unusual intensity changes in the infrared spectra of the enflurane···acetone complexes: spectroscopic and theoretical studies

Blue-shifting C-H···O hydrogen-bonded complexes between enflurane (CHFCl-CF(2)-O-CHF(2)) and deuterated acetone have been identified in CCl(4) solution by FT-IR spectroscopy. For the two ν(C-H) stretching vibrations of enflurane the observed blue shifts are +17 and +11 cm(-1). The corresponding two infrared ν(C-H) bands show the opposite changes of their intensity, one is decreasing, and the other is significantly increasing, upon formation of the hydrogen bonding. The structures, binding energies, and theoretical infrared spectra of the enflurane-acetone complexes were calculated by MP2 and B3LYP methods using the 6-311++G(d,p) basis set. The interaction energies were evaluated by the complete basis set limit (CBS) calculations at the HF, MP2, and CCSD(T) levels of theory. Although the MP2 method slightly overestimates the blue shifts, the MP2 predicted frequency difference and the relative IR intensities of two ν(C-H) stretching bands for the enflurane-acetone complexes show good agreement with experiment. Unfortunately, the B3LYP method predicts incorrect IR intensities of these hydrogen-bonded systems. The NBO analysis was performed to unravel the origin of the unusual intensity changes of two ν(C-H) stretching bands, in enflurane complexes.     

Vibrational frequencies and infrared intensities of acetonitrile coordinated with metal cations: an ab initio study

Vibrational frequencies and infrared intensities have been calculated at the 6-31G and 6-31G^** levels for acetonitrile and for the complexes of acetonitrile with Li⁺ and Na⁺ cations. The changes in the infrared characteristics from an isolated acetonitrile to acetonitrile coordinated with metal cations (Li⁺ and Na⁺) have been evaluated. The ab initio calculations predict an essential increase of the intensities of the stretching CN, C-C and deformation CH₃, CCN vibrations in the complexes of acetonitrile with Li⁺ and Na⁺ cations.     

How Accessible Is Atomic Charge Information from Infrared Intensities? A QTAIM/CCFDF Interpretation

Infrared fundamental intensities calculated by the quantum theory of atoms in molecules/charge-charge flux-dipole flux (QTAIM/CCFDF) method have been partitioned into charge, charge flux, and dipole flux contributions as well as their charge-charge flux, charge-dipole flux, and charge flux-dipole flux interaction contributions. The interaction contributions can be positive or negative and do not depend on molecular orientations in coordinate systems or normal coordinate phase definitions, as do CCFDF dipole moment derivative contributions. If interactions are positive, their corresponding dipole moment derivative contributions have the same polarity reinforcing the total intensity estimates whereas negative contributions indicate opposite polarities and lower CCFDF intensities. Intensity partitioning is carried out for the normal coordinates of acetylene, ethylene, ethane, all the chlorofluoromethanes, the X(2)CY (X = F, Cl; Y = O, S) molecules, the difluoro- and dichloroethylenes and BF(3). QTAIM/CCFDF calculated intensities with optimized quantum levels agree within 11.3 km mol(-1) of the experimental values. The CH stretching and in-plane bending vibrations are characterized by significant charge flux, dipole flux, and charge flux-dipole flux interaction contributions with the negative interaction tending to cancel the individual contributions resulting in vary small intensity values. CF stretching and bending vibrations have large charge, charge-charge flux, and charge-dipole flux contributions for which the two interaction contributions tend to cancel one another. The experimental CF stretching intensities can be estimated to within 31.7 km mol(-1) or 16.3% by a sum of these three contributions. However, the charge contribution alone is not successful at quantitatively estimating these CF intensities. Although the CCl stretching vibrations have significant charge-charge flux and charge-dipole flux contributions, like those of the CF stretches, both of these interaction contributions have opposite signs for these two types of vibrations.     

An absolute integrated infrared intensity study of (η6C6H5R)Cr(CO)2(CS) (R = H,Me, Cl,CO2Me)

The absolute integrated i.r. intensities of the CO and CS stretching bands of the thiocarbonyl complexes (η⁶C₆H₅R)Cr(CO)₂(CS), where R = H, Me, Cl and CO₂Me, have been determined in CS₂ solutions. The intensities have been correlated with each other and with the band wavenumbers, and have been shown to be dependent on the nature of the substituent R in the aromatic ring. The intensities have been demonstrated to be better probes of the electronic effects occurring in these complexes than are the wavenumbers, and correlate well with the Hammett substituent parameters, σ⁰.     

Fourier transform infrared spectroscopy and ab initio theory of acid-hydrogen sulfide clusters: H2S-HCl, D2S-DCl and H2S-(HCl)(2)

The rotationally resolved Fourier transform infrared (FTIR) spectrum of the nu(s) HCl and DCl stretching bands for the hydrogen bonded complex H2S-HCl and its isotopomer D2S-DCl have been observed in a supersonic jet at 0.02 cm(-1) resolution. In the same experimental conditions, two additional bands observed without rotational structure in the HCl range of the dimer have been assigned to the cyclic trimer H2S-(HCl)(2). The multidimensional coupling picture involving the donor stretch mode nu(s) and low frequency intermolecular modes already evidenced in several medium strength hydrogen bonded complexes is beautifully confirmed by the observation of completely separated hot band progressions in the 198 K cell spectrum of both dimers. Based on our anharmonic adiabatic approach for the treatment of the coupled vibrations, absolute vibrational frequencies, diagonal and off-diagonal anharmonicities as well as rovibrational coupling constants obtained from analyses of several 2-D subspaces at MP2 and CCSD(T) level are in excellent agreement with spectroscopic results. In the case of small light complexes, the combination of elevated rotational constants and a negligible contribution of intramolecular vibrational redistribution (IVR) improve the reliability of predissociation lifetime measurements, estimated to 180 ps for H2S-HCl and above 200 ps for D2S-DCl.     

稀土乙酰丙酮络合物的拉曼光谱(Ⅱ)

本文从拉曼光谱观察水合分子对无水、一水、三水稀土乙酰丙酮络合物的金属-氧(M-O)拉伸振动带的影响,发现无水络合物在400cm^-1附近只有一个振动带,一水络合物在400和415cm^-1附近有两个强度不等的振动带,它们的M-O振动频率随原子序数变化都呈“四分组”效应,而三水络合物400cm^-1附近带变形,且随轻、重稀土而异,从而干扰了镧系变化规律,没有系统的“四分组”效应。由于一水络合物415cm^-1附近带随脱水而消失,吸水而复现的可逆实验事实,修正了前文对415cm^-1附近带的指定,而归属于(M-O)H₂。络合物M-O拉伸带随水合分子变化反映灵敏,出现特征带形。     

Experimental and theoretical investigation of vibrational overtones of glycolic acid and its hydrogen bonding interactions with water

The present work reports observations of the 4nu(1) and 4nu(2) O-H stretching transitions in glycolic acid, CH(2)OHCOOH, using a highly sensitive cavity ring-down spectrometer. Experimental and theoretical values for the harmonic frequencies and anharmonic constants of both O-H stretching transitions were extracted and are compared with theoretical calculations in the literature. Calculations of anharmonic frequencies, intensities, and relative energies have been performed and are presented for three conformers of glycolic acid. In the presence of water, an interesting broad spectral feature appeared underneath 4nu(1) and 4nu(2). New calculations for harmonic frequencies, intensities, and relative energies of four CH(2)OHCOOH-H(2)O complexes are reported to aid in understanding the observed spectrum. This work suggests that the perturbations are caused by intermolecular hydrogen bonding of glycolic acid with one or more water molecules.     

DFT calculations on the cyclic ethers hydrogen-bonded complexes: molecular parameters and the non-linearity of the hydrogen bond

B3LYP/6-311+G(d,p) calculations were used to explore the geometry, intermolecular energy and the vibrational harmonic spectrum of heterocyclic complexes formed between 2,5-dihydrofuran and thiophene cyclic ethers and the HCl and HF acids. The simulated structures of these hydrogen complexes are discussed in terms of the linearity deviation of the n...HX hydrogen bond. Theoretical results are satisfactory as compared to the experimental equilibrium structure. The energies of the hydrogen bonds were determinate through the difference between the complex and its correspondent isolated monomers. Moreover, to obtain the correct energies of the hydrogen bonds, it was included the values of the zero point vibrational energy and the basis set superposition error. The infrared spectra reveal the direct relationship between the distance of the hydrogen bond and its stretching frequencies, as well as a good interpretation of the bathochromic effect of the HCl and HF stretching modes from intermolecular charge transfer.     

Hydrogen-bonded complexes of nitrous and nitric acids with ethene Ab initio and DFT studies

The complexes formed by ethene with nitric and nitrous (trans and cis) acids have been investigated by ab initio (SCF and MP2) and B3LYP calculations with 6-311++G(d,p) basis set. Full geometry optimisation has been performed for the complexes studied. The most stable structures of the complexes are established. Bearing in mind the corrected values of the dissociation energy the studied hydrogen-bonded complexes can be ordered as follows: C(2)H(4)...HONO(2)>C(2)H(4)...HONO-trans>C(2)H(4)...HONO-cis. In the complexes the acids act as proton donors forming the pi-type of hydrogen bond with ethene. The predicted changes in the vibrational characteristics (vibrational frequencies and infrared intensities) arising from the hydrogen bonding are in good agreement with the experimentally measured. The predicted frequency shift of the stretching OH vibration in the nitric acid is largest (-210 cm(-1)), followed by the shifts in the trans-HONO (-141 cm(-1)) and cis-HONO (-109 cm(-1)). The calculations predict an increase of the IR intensity of the stretching O-H vibration in the complexes from 6 to 10 times.     

Frequencies and absorption intensities of the fundamental and the first overtone of NH stretching vibrations of pyrroleacetylene and pyrroleethylene complexes studied by density-functional-theory calculation

The structures of pyrroleacetylene and pyrroleethylene complexes which form an NH–π hydrogen bonding were calculated by density-functional-theory calculation. The wavenumbers and absorption intensities of the fundamental and the first overtone of NH stretching of the complexes were investigated to compare effects of the hydrogen bonding on the fundamental and the first overtone of the NH stretching mode. One-dimensional Schrödinger equation in consideration of molecular vibrational anharmonicity was used for the estimation of the wavenumbers and absorption intensities of NH stretching modes of the complexes; it was found that the NH–π hydrogen-bond formation induced lower wavenumber shift for both the fundamentals and first-overtones of NH stretching mode and it increases absorption intensities of the fundamentals and decreases those of first overtones of NH stretching mode.     

Vibrational dynamics of hydrogen‐bonded HCN complexes with OH and NH acids: Computational DFT systematic study

Vibrational properties (band position, infrared [IR], and Raman intensities) of C?N stretching mode were studied in 65 gas phase hydrogen‐bonded 1:1 complexes of HCN with OH acids and NH acids using density functional theory (DFT) calculations at the B3LYP‐6‐311++G(d,p) level. Furthermore, general characteristics of the hydrogen bonds and vibrational changes in acids OH/NH stretching bands were also considered. Experimentally observed blue shift of the C?N stretching band promoted by hydrogen bonding, which shortens the triple bond length, is very well reproduced and quantitatively depends on the hydrogen bond length. Both IR and Raman ν(C?N) band intensities are enhanced, also in good agreement with the experimental results. IR intensity increase is a direct function of the hydrogen bond energy. However, the predicted Raman intensity raise is a more complex function, depending simultaneously on characteristics of both the hydrogen bond (C?N bond length) and the H‐donating acid (polarizability). With these two parameters, ν (C?N) Raman intensities of the complexes are explained with a mean error of ±2.4%. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Quantitative relationships between bond lengths,stretching vibrational frequencies,bond force constants,and bond orders in the hydrogen-bonded complexes involving hydrogen halides

To uncover the correlation between the bond length change and the corresponding stretching frequency shift of the proton donor D–H upon hydrogen bond formation, a series of hydrogen-bonded complexes involving HF and HCl which exhibit the characteristics of red-shifted hydrogen bond were investigated at the MP2/aug-cc-pVTZ, M062X/aug-cc-pVTZ, and B3LYP/aug-cc-pVTZ(GD3) levels of theory with CP optimizations. A statistical analysis of these complexes leads to the quantitative illustrations of the relations between bond length and stretching vibrational frequency, between bond length and bond force constant, between stretching vibrational frequency and bond force constant, between bond length and bond order for hydrohalides in a mathematical way, which would provide valuable insights into the explanation of the geometrical and spectroscopic behaviors during hydrogen bond formation.     

Experimental infrared spectra of matrix isolated complexes of HCl with 4-substituted pyridines. Evaluation of anharmonicity and matrix effects using data from ab initio calculations

Infrared spectra have been measured for HCl complexes with 4-cyanopyridine, 4-chloropyridine, pyridine and 4-methylpyridine isolated in argon and nitrogen matrices at about 12 K. The experimental spectra are dramatically different from computed MP2/6-31+G(d,p) harmonic spectra, a consequence of the anharmonicity of the potential energy surface in the hydrogen-bonding region. Comparisons of computed and experimental data suggest that the experimental spectra correspond to complexes with HCl distances that are much longer than the computed equilibrium distances. These longer distances, R_cor(HCl), are related to the average HCl distance in the ground vibrational state of the proton-stretching mode. The value of R_cor(HCl) determines values of three effective anharmonic force constants for the HCl stretch, the NH stretch and the coupling between them for each complex. The simulated anharmonic spectra obtained when these anharmonic force constants are used in place of the corresponding harmonic constants show spectral patterns with respect to both frequencies and intensities that are very similar to those observed in the experimental spectra obtained in Ar and N₂ matrices. 1D anharmonic potential curves related to the experimental spectra are presented. They provide insight into anharmonicity of the hydrogen-bonded proton stretch for these systems, and into the sensitivity of the potential energy surface to the environment.     

Hydrogen Bonding in Pyridine N-Oxide/Acid Systems: Proton Transfer and Fine Details Revealed by FTIR, NMR, and X-ray Diffraction

The H-bonded complexes of pyridine N-oxide (PyO) with H(2)O, acetic, cyanoacetic, propiolic, tribromoacetic, trichloroacetic, trifluoroacetic, hydrochloric, and methanesulfonic acids have been studied by FTIR and NMR spectroscopy, X-ray diffraction, and quantum chemical DFT calculations. Correlations between vibrational frequencies of the NO stretching and PyO ring modes and geometric parameters of the H-bond have been established. FTIR experiments show and DFT calculations confirm that definite discontinuity is present in the vicinity of the midpoint in the proton transfer pathway. The established correlations significantly aid in the understanding of fine effects such as the isotope (deuteration) effect, crystal-to-solution transition, or criticality of aqueous solutions induced by ionic pairs. Geometric isotope effect in the ionic H-bond aggregate of PyO·H(D)Cl was found to be extraordinary large. Measured FTIR, CP/MAS, and high-resolution (13)C NMR spectra indicate that H-bond in the PyO·HCl complex in polar solvent can potentially be more ionic than in the crystal. Vibrational modes of ionic pairs originating via proton transfer in H-bond complexes can provide new information concerning the interionic interaction and its role in the phase separation and mezo-structuring processes. The results are compared to the relevant data for PyO·HCl complex in argon matrix.     

Theoretical calculations of the molecular properties of maleimide and its dimer

B3LYP theoretical calculations with 6-31++G(d,p) basis set have been performed to study the infrared spectrum of maleimide and its dimer. Our calculations have shown that the dimer formation leads to a binding energy of 44.0kJmol(-1) involving two intermolecular hydrogen bonds between the amide hydrogen and a carbonyl group of two neighboring maleimides. This value is essentially due to the electrostatic interaction term. Our calculations have also revealed the vibrational changes, in terms of frequencies and IR intensities, after dimer formation. The most affected modes are associated with the NH stretching and in-plane bending bands. This behavior can be adequately interpreted by the hydrogen atomic charge and NH charge-flux based on the modified charge-charge flux-overlap model for infrared intensities. The B3LYP frequency shifts are in very good agreement with the experimental ones.     

Density Functional Theory Study of the Interaction between Guanine and Catechin

The interacting patterns and mechanism of the catechin and guanine have been investigated with the density functional theory B3LYP method by 6‐31G* basis set. Fourteen stable structures for the catechin‐guanine complexes have been found which form two hydrogen bonds at least. The results indicate that the complexes are mainly stabilized by the hydrogen bonding interactions. At the same time, the number and strength of hydrogen bond play a co‐determinant parts in the stability of the complexes which can form two or more hydrogen bonds. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) have been adopted to investigate the hydrogen bonds involved in all systems. The interaction energies of all complexes have been corrected for basis set superposition error (BSSE), ranging from ?38.86 to ?14.56 kJ/mol. The results showed that the hydrogen bonding contributes to the interaction energies dominantly. The corresponding bonds stretching motions in all complexes are red‐shifted relative to that of the monomer, which is in agreement with experimental results.     

氟喹诺酮类抗生素与磷钨酸体系的共振瑞利散射光谱研究及其分析应用

在5.0 mol/L的HCl缓冲介质中,磷钨酸（Pwa）与莫西沙星(MXFX)和加替沙星（GTF）等氟喹诺酮类抗生素(FLQs)相互作用形成摩尔比1∶1离子缔合物,导致体系的共振瑞利散射(RRS)显著增强并出现新的RRS光谱。 MXFX和GTF的反应产物具有相似的光谱特征,最大散射波长位于320 nm附近,且药物浓度与散射增强(ΔI)成正比,2种氟喹诺酮类药物的线性范围分别为0.025~6.0 mg/L（MXFX）和0.023~9.0 mg/L（GTF）。 据此可建立用于测定氟喹诺酮类药物的简捷快速灵敏的新方法,方法用于胶囊和人尿液中的FLQs测定并取得满意结果。 并对反应机理和RRS增强的原因进行了讨论。     

Vibrational spectroscopic properties of hydrogen bonded acetonitrile studied by DFT

Vibrational properties (band position, Infrared and Raman intensities) of the acetonitrile C[triple bond]N stretching mode were studied in 27 gas-phase medium intensity (length range: = 1.71-2.05 angstroms; -deltaE range = 13-48 kJ/mol) hydrogen-bonded 1:1 complexes of CH3CN with organic and inorganic acids using density functional theory (DFT) calculations [B3LYP-6-31++G(2d,2p)]. Furthermore, general characteristics of the hydrogen bonds and vibrational changes in the OH stretching band of the acids were also considered. Experimentally observed blue-shifts of the C[triple bond]N stretching band promoted by the hydrogen bonding, which shortens the triple bond length, are very well reproduced and quantitatively depend on the hydrogen bond length. Both predicted enhancement of the infrared and Raman nu(C[triple bond]N) band intensities are in good agreement with the experimental results. Infrared band intensity increase is a direct function of the hydrogen bond energy. However, the predicted increase in the Raman band intensity increase is a more complex function, depending simultaneously on the characteristics of both the hydrogen bond (C[triple bond]N bond length) and the H-donating acid polarizability. Accounting for these two parameters, the calculated nu(C[triple bond]N) Raman intensities of the complexes are explained with a mean error of +/- 2.4%.