The infrared spectrum of bis(fluorosulfonyl)imide revisited: Attractive performances of the PBE0/6-31G** model

We report a systematic investigation of the far- and mid-infrared spectra of ionic liquids (ILs) containing the bis(fluorosulfonyl)imide (FSI) anion, both in the liquid state at room temperature and in solid phases at low temperatures. We extended to lower frequencies a previous study, and we observed four additional vibration bands below 500 cm⁻¹, attributable to FSI. Moreover, DFT calculations of vibration frequencies were performed using three combinations of theory and basis set: (1) B3LYP/6-31G**, (2) B3LYP/6-311 + G(3df) and (3) PBE0/6-31G**. Model 1, largely used in the previous literature concerning ILs, shows the poorest performances; model 2, which generally gives a good agreement with the experiments, misses the vibration frequencies by ∼40 cm⁻¹ in the range 650–900 cm⁻¹ where one finds the largest spectral differences between cis- and trans-FSI; model 3 gives the best agreement with the experiments and, moreover, is much less time consuming than model 2. The comparison with calculations suggests that the band centered around 1217 cm⁻¹ is a good marker of the occurrence of the cis-FSI conformer. Finally, the bands located around 730 and 750 cm⁻¹ are attributable to cis- and trans- conformer of FSI, respectively.     

Intramolecular mobility and phase transitions in ammonium oxofluoroniobates (NH4)2NbOF5 and (NH4)3NbOF6, a NMR and DFT study

Molecular structure, ionic mobility and phase transitions in six- and seven-coordinated ammonium oxofluoroniobates (NH₄)₂NbOF₅ and (NH₄)₃NbOF₆ were studied by ¹⁹F, ¹H NMR and DFT calculations. Equatorial fluorine atoms (F_eq) in [NbOF₅]²⁻ and [NbOF₆]³⁻ are characterized by high ¹⁹F NMR chemical shifts while axial fluorine atoms (F_ax) have those essentially lower. The high-temperature ionic mobility in (NH₄)₂NbOF₅ does not stimulate the ligand exchange F_eq ↔ F_ax, whereas it is observed in (NH₄)₃NbOF₆ as pseudorotation typical for seven-coordinated polyhedra. The transformation of pentagonal bipyramidal structure (BP) of [NbOF₆]³⁻ into capped trigonal prismatic (CTP) one takes place during the phase transition (PT) at 260 K. The PT of order-disorder type in (NH₄)₂NbOF₅ is accompanied by transition of anionic sublattice to a rigid state. The ¹⁹F and ¹H NMR data corroborate the independent motions of NH₄ groups and anionic polyhedra in (NH₄)₂NbOF₅ while they are coordinated in (NH₄)₃NbOF₆.     

Strong intramolecular hydrogen bonds. Part I. Vibrational frequencies of the OH group in some picolinic acid N-oxides predicted from DFT calculated potentials and located in the infrared spectra

Hydrogen bonding in picolinic acid N-oxide (I), its 4-nitro (III), 4-methoxy (IV), 4-amino (V) derivatives and in quinaldic acid N-oxide (II) was characterized by calculations (B3LYP/6-31G(d)) of metric parameters, H-bond energies and one-dimensional proton potential functions with vibrational energy levels. Solvent effects were estimated by the SCRF PCM method of Tomasi and coworkers (J. Tomasi, M. Persico, Chem. Rev. 94 (1994) 2027). The potential functions are strongly asymmetric with the energy minimum placed near the carboxylic oxygen. The inflection near the NO oxygen develops into a second, shallower minimum under the SCRF.

Empirical assignments of the OH stretching and bending modes were made for (I)–(IV). The stretchings of (I, II) and (IV) in various solvents are observed in the region 1600–1300 cm⁻¹, but near 2600 cm⁻¹ for (III). The calculated and observed frequencies are in fairly good agreement with theoretical predictions reflecting the electronic effects of the substituents upon the H-bond strength. The observed trends in the solvent effects upon various parameters characterizing the H-bonding also correspond to predictions.     

The infrared and Raman spectra, ab initio calculations and spectral assignments of cyclopropylmethyl dichlorosilane (c-C3H5)SiCl2CH3

Raman spectra of cyclopropylmethyl dichlorosilane (c-C₃H₅)SiCl₂CH₃ as a liquid were recorded at 293 K and polarization data were obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163 K, and intensity changes of certain bands with temperature were detected. No crystallization was ever obtained in the Raman cryostat in spite of extensive annealing. The infrared spectra have been studied as a vapour, as an amorphous solid at 78 K and as a liquid in the range 600-100 cm⁻¹. No infrared bands present in the vapour or liquid seemed to vanish upon cooling, and the sample never formed crystals on the CsI window of an infrared cryostat.The compound exists a priori in two conformers, syn and gauche, and the experimental results suggest an equilibrium in which the gauche conformer has 1.64 kJ mol⁻¹ lower enthalpy than syn in the liquid, leading to 20% syn at ambient temperature. Most of the syn bands were situated close to the corresponding gauche bands and it was difficult to obtain reliable ΔH values.B3LYP calculations with various basis sets and the CBS-QB3 and G2 and G3 models were employed, yielding the conformational enthalpy difference ΔH (syn-gauche) between 2.6 and 3.4 kJ mol⁻¹. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the syn and gauche conformers were calculated. Instead of scaling the calculated wavenumbers in the harmonic approximation, calculations from B3LYP/cc-pVTZ were derived in the anharmonic approximation. In most cases these values were in good agreement with the experimental results for 38 observed modes of the gauche and 8 modes of the syn conformer with a deviation of ca. 1%.     

Molecular and electronic structures, infrared spectra, and vibrational assignment for ap and sc conformers of hexafluoro-iso-propanol

Comprehensive studies of the molecular structures, vibrational frequencies and infrared intensities of the antiperiplanar (ap) and synclinal (sc) conformers of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) have been performed by the density functional (B3LYP) method using the extended 6-311++G(df,pd) basis set. The detailed natural bond orbital (NBO) analysis has revealed the nature of the hyperconjugative interactions, which stabilize each conformer, in the gas phase. The mid-infrared spectra of HFIP in carbon tetrachloride solution were measured, and the experimental intensities of each conformer were obtained by the curve–resolution procedure. The relative abundance of the two conformers, calculated from the relative intensities, shows nearly equimolar ratio (N_sc/N_ap ≈ 1), in this solution. The DFT-predicted frequencies show very good agreement with the experimental data. The clear-cut vibrational assignment for each conformer is reported on the basis of the calculated potential energy distributions. Several controversies in an earlier assignment of HFIP have been elucidated.     

Scaled quantum chemical calculations and FTIR, FT-Raman spectral analysis of 3,4-diamino benzophenone

The vibrational spectra of 3,4-diamino benzophenone (DABP) have been computed using B3LYP methodology and 6-31G* and 6-31G** basis sets. The solid phase FTIR and FT-Raman spectra were recorded in the region 4000-400 cm-1 and 3500-100 cm-1, respectively. A close agreement was achieved between the observed and calculated frequencies by employing normal coordinate calculations. The observed and simulated spectra were found to be well comparable.     

Infrared and Raman studies of phase transitions in metal–organic frameworks of [(CH3)2NH2][M(HCOO)3] with M=Zn,Fe

We report on temperature-dependent infrared (IR) and Raman studies of [(CH₃)₂NH₂][M(HCOO)₃] metal–organic frameworks (MOFs) with M=Zn, Fe. Based on Raman and IR data, an assignment of the observed modes to respective vibrations of atoms is proposed. Temperature-dependent studies revealed abrupt changes below 160 K that are attributed to the onset of first-order structural phase transition. The most pronounced changes are observed for the modes corresponding to the dimethylammonium cation, especially those involving motion of hydrogen atoms. This behavior proves that the phase transition has an order–disorder character and is associated with the ordering of protons. The abrupt splitting of some modes related to the formate ion indicates that this transition is also associated with significant distortion of the metal-formate framework.     

烷基咪唑型卤盐类离子液体的合成机理研究

用密度泛函理论考察了甲基咪唑和一系列的卤代烷烃(氯乙烷,氯丁烷,溴乙烷,溴丁烷)反应合成咪唑类离子液体的反应机理. 在B3LYP/6-31++G**//B3LYP/6-31G*基组水平上找到了两条反应路径：路径A(反应物→TS1→P1)和路径B(反应物→TS2→P2). 在路径A中, 卤素离子和咪唑环C2上的氢质子形成氢键;在路径B中, 卤素离子和咪唑环C5上的氢质子形成氢键. 计算发现, 氢键的形成在反应中起到了非常重要的作用, 特别是咪唑环C2上的氢质子在和卤素离子成氢键后形成了一个五员环结构的过渡态, 该过渡态能量较低. 经过渡态TS1的反应途径其活化能要低于经过渡态TS2的反应途径, 反应路径A为主要的反应通道. 计算结果表明, 经过渡态TS1的反应途径是一放热过程, 这和实验观察现象一致.     

Molecular analysis of water clusters: Calculation of the cluster structures and vibrational spectrum using density functional theory

Density functional theory (DFT) is applied to obtain absorption spectra at THz frequencies for molecular clusters of H₂O. The vibrational modes of the clusters are calculated. Coupling among molecular vibrational modes explains their spectral features associated with THz excitation. THz excitation is associated with vibrational frequencies which are here calculated within the DFT approximation of electronic states. This is done for both isolated molecules and collections of molecules in a cluster. The principal result of the paper is that a crystal-like cluster of 38 water molecules together with a continuum solvent background is sufficient to replicate well the experimental vibrational frequencies.     

Convenient synthesis of various ionic liquids from onium hydroxides and ammonium salts

Hydroxide ionic liquids, such as 1-alkyl-3-methylimidazolium hydroxides, undergo smooth anion metathesis with ammonium salts to produce a variety of ionic liquids in excellent yields. It is a practical supplement of traditional neutralization method due to the broader range of starting materials containing desired anions.     

Thermal Destiny of an Ionic Crystal

Recently it has been shown that defect‐defect interactions leading to anomalous rise in defect concentrations and eventually to phase transitions into a disordered state can be successfully described by a quasi defect lattice model [1]. Using this approach the fact is highlighted that the evolution of an ionic crystal from the perfect state at T = 0 K to a weakly defective ideal crystal and eventually via passing a pre‐melting regime to a superionic crystal (or melt) is unavoidable (given sufficient stability) and can be roughly phenomenologically calculated by using a few basic parameters only. Semi‐empirical relations (e. g. Tammann rule) can be quantified in this way.     

Self- and heteroassociates of cumyl hydroperoxide: FTIR-spectroscopy, chemometrics (factor analysis) and quantum chemical calculations

Self- and heteroassociation of cumyl hydroperoxide and acetophenone in n-decane solutions were studied by FTIR spectroscopy (3100–3700 cm⁻¹, 298–358 K). To interpret spectroscopic data, the new approach of factor analysis was offered. Equilibrium constants and thermodynamic parameters of associate formation were determined. The DFT calculations of cumyl hydroperoxide conformations, their self- and heteroassociates were carried out.     

Density functional theory study on the –SO3H functionalized acidic ionic liquids

In this work, the structures of the –SO₃H functionalized acidic ionic liquid 1-(3-sulfonic acid) propyl-3-methylimidazolium hydrogen sulfate ([C₃SO₃Hmim]HSO₄), including its precursor compound (zwitterion), cation, and cation–anion ion-pairs, were optimized systematically by the DFT theory at B3LYP/6-311++G** level, and their most stable geometries were obtained. The calculation results indicated that a great tendency to form strong intramolecular hydrogen bonds was present in the zwitterion, and this tendency was weakened in the cation that was the protonation product of zwitterion. The intramolecular hydrogen bonds and intermolecular hydrogen bonds coexisted in the ionic liquid, and they played an important role in the stability of the systems. The strongest interaction in the ionic liquid was found between the anion and the functional group. The transition state research and the intrinsic reaction coordinate analysis of the hydrogen transfer reaction showed that, when the cation and the anion interacted near the functional group by double O–H···O hydrogen bonds, the ionic liquid was inclined to exist in a form of the zwitterion and H₂SO₄.     

Medium Effect on the Rotational Isomerism in 1,3,5-Triacetylbenzene

Summary. The optimal geometries, energies, polarities, infrared frequencies, and intensities of the non-polar and polar conformers of 1,3,5-triacetylbenzene were calculated using DFT/B3LYP/6-311G** and semi-empirical (AM1 and PM3) methods. All the methods revealed that the non-polar conformer prevails in vacuum. The infrared spectra in the solid state, in Ar matrix, and in liquid solutions as well as the dipole moments of 1,3,5-triacetylbenzene in many solvents show the distinct influence of the environment on the non-polar conformer ⇌ polar conformer equilibrium. The effect of solvent polarity on the standard Gibbs energy of this conformational equilibrium is quantitatively discussed in terms of the continuum-homogenous dielectric model.     

An experimental and theoretical study of molecular structure and vibrational spectra of 2-chloronicotinic acid by density functional theory and ab initio Hartree–Fock calculations

In this work, the Fourier transform Raman and Fourier transform infrared spectra of 2-chloronicotinic acid (2-CNA) are recorded in the solid phase. The molecular geometry, vibrational frequencies, infrared intensities and Raman scattering activities of 2-CNA in ground state have been calculated by using ab initio Hartree–Fock (HF) and density functional (B3LYP and B3PW91) methods with 6-31G(d) and 6-311G(d) basis sets level. On the basis of the comparison between calculated and experimental results and the comparison with related molecule, assignments of fundamental vibrational modes are examined. The optimized geometric parameters (bond lengths and bond angles) obtained by using HF show the best agreement with the experimental values of 2-CNA. Comparison of the observed fundamental vibrational frequencies of 2-CNA and calculated results by density functional (B3LYP and B3PW91) and Hartree–Fock methods indicates that B3LYP is superior to the scaled Hartree–Fock and B3PW91 approach for molecular vibrational problems.