V. D. Maiorov

IR Study of ion-molecular interactions in a DMF-HCl system

The Multiple Attenuated Total Reflection (MATR) IR-spectra of HCl solutions in DMF (0–48.55% HCl) were recorded and analyzed in the range of 900–4000 cm−1. Depending on the ratio of compounds, a variety of complexes (2 DMF) · HCl (1), DMF · HCl (2), DMF · (2 HCl) (3) are formed in the system. The concentrations of the complexes were measured. Complex2 possesses a quasi-ionic structure Me2NHCO...H...Cl. The addition of a DMF molecule to complex2 with formation of complex1 does not result in destruction of the quasi-ionic structure of the DMF-HCl bond. In excess HCl, this structure is decomposed and the complex with the ion pair structure Me2NHCOH+ (ClHCl)− is formed.

IR SPECTROSCOPIC STUDY OF ION-MOLECULAR INTERACTIONS IN THE METHANESULFONIC ACID-N, N-DIMETHYLFORMAMIDE SYSTEM

Complex formation in the methanesulfonic acid (MSA)-DMF system was studied by Multiple Attenuated Total Reflectance (MATR) IR spectroscopy at 30°C within the composition range from neat MSA up to neat DMF. Depending on the ratio of components, two types of complexes with a strong quasi-symmetrical H bond (1 and2) are formed. The uncharged complex1 is a quasi-ion pair with the (O…H…O) bridge. Complex2 is formed by a protonated DMF molecule and the (A…H…A)− anion bound as an ion pair. It is established that complexes1 are solvated by DMF molecules in an excess of a base. Solvation or2 in an excess of an acid corresponds to a change from contact to contact-separated ion pairs. Continuous absorption spectra of charged and uncharged complexes1 and2 were obtained. The schemes of acid-base interactions in the MSA-DMF and HCl-DMF systems were compared.

Complexes with strong symmetric hydrogen bonds and their solvation in the trifluoroacetic acid—N,N-dimethylformamide system studied by IR spectroscopy

Complex formation in the trifluoroacetic acid (TFA)—DMF system containing TFA from 0 to 100 mol.% was studied by IR multiple attenuated total reflectance (MATR) spectroscopy at 30°C. The formation of uncharged 1∶1 TFA—DMF complexes with a quasi-ion structure and partial proton transfer to the O atom of the DMF molecule (quasi-ion pairs) were observed in the TFA—DMF system with the TFA content from 0 to 90 mol%. Depending on the ratio of the components, the quasi-ion pairs are solvated by the DMF or TFA molecules. The solvation of the quasi-ion pairs slightly changes the parameters of the central strong H bond. When the acid concentration reaches 80 mol.%, the proton adds to the DMF molecule to form the ion pair (DMF)H+·(A...H...A)−, whose anion contains a strong symmetric H bond.

Infrared spectra of negative ions with a strong, symmetric hydrogen bond (HO...H...OH)− and (H3CO...H...OCH3)−

From the multiple attenuated total internal reflection (MATIR) infrared spectrum of an aqueous KOH solution, the spectrum of the (HO)2H− ion, formed by a strong, symmetric H-bond, has been segregated. The spectrum of the analogous ion (CH3O)2H− has been segregated from the MATIR infrared spectrum of a solution of KOCH3 in methanol. The segregated spectra contain large numbers of individual bands that are not present in the spectra of the original components of the solution. This may be a consequence of strong interaction of vibrations of the proton in the central strong, symmetric hydrogen bond with vibrations of other groups in the ion.

IONS WITH A STRONG SYMMETRIC H-BOND IN SOLUTIONS OF SODIUM ACETATE IN ACETIC ACID

The multiple attenuated total reflection IR spectra of solutions of sodium acetate in acetic acid have been recorded in the range from 9000 to 4000 cm−1. The CH3COO− anion and an acid molecule form be complex (CH3COO...H...OOCCH3) with a strong symmetric H-bond.

Raman spectra of complexes of HCl with DMF with a strong quasisymmetric H-bond in solutions

Raman spectra of complexes of HCl with DMF with a strong quasisymmetric H-bond in solutions were obtained. The formation of these complexes is accompanied by significant changes in almost all the vibration frequencies and line intensities, the changes in Raman and IR spectra being similar in many features. A weak background scattering was found in the Raman spectra, which coincides in shape with the continuous absorption in IR spectra.

Ion-molecular composition of the methanesulfonic acid-water system from IR spectroscopic data

Conclusions1.The equilibrium compositions and structures of the ionic and molecular complexes in the CH3SO3H-H2O system over the entire range of the concentrations of the components were determined by IR spectroscopy; the highest concentration of the anionic forms is reached at a water:acid ratio of 2∶1.2.Primarily H5O2+ ions are formed at high acid concentrations, and the presence of CH3SO3H·OSO2CH3 complexes was also revealed.3.The coefficients of continuous absorption in dilute and concentrated solutions of CH3SO2OH were determined. The unusually high value of the coefficient of continuous absorption for the concentrated region is associated with the presence in solution of (CH3SO2O...H...OSO2CH3)− ions with a strong quasisymmetrical hydrogen bond.

The Structure of DMF · HCl and DMF · (HCl)2 Complexes according to ab initio Calculations

Based on ab initio calculation at the 6-31G level, the differences in the structures of isolated complexes of DMF with HCl with compositions 1 : 1 and 1 : 2 are analyzed. The interaction of HCl with DMF results in the formation of the molecular complex. When HCl is added to this complex, a proton transfers to the DMF molecule and the asymmetric fragment Cl···HCl is formed. Calculated data are compared with the structures of DMF complexes with HCl in the condensed phase.

The structure of complexes of HCl withN,N-dimethylformamide based on polarization measurements in the Raman spectra

The Raman spectra of solutions of HCl in DMF were studied and the degree of depolarization of spectral lines was measured. Complexes of three types, 2DMF·HCl, DMF·HCl, and DMF·2HCl, are formed depending on the ratio of the components. Examination of the structure of the contour of the v(C=O) line showed that the acid-base interactions in the complexes occur through the O atom of the DMF molecule. On the basis of polarization measurements it was established that two DMF molecules in the 2DMF·HCl complex are nonequivalent.

An investigation of proton solvation in aqueous sulfuric acid solutions based on the 1700 cm−1 absorption band in their IR spectra

Conclusions1.Following the method of frustrated total internal reflection and working at 30‡C, we have measured the change in the optical density of the H-O-H group deformation vibration band in the spectrum of the hydrated protons in aqueous 4.96–98.49% H2SO4 solutions. In dilute acid solutions the proton is firmly solvated with two water molecules to form the (H2O... H...OH2)+ ion; in more concentrated solutions there is not enough water to permit each dissociated proton to solvate in this way, and solvation leads to the formation of (H2O...H... OR)+ ions in which OR is some part of the acid molecules.2.The measured values of the optical density have been used to calculate equilibrium concentrations of the H5O2+ and H3O2R+ ions in 60.36–85.70% H2SO4 solutions. In aqueous H2SO4 solutions the point of the H3O2R++H2O ⇄ H3O2++OR equilibrium is not completely displaced toward the right (OR is a part of the acid molecule).