The ab initio study of halogen and hydrogen σN-bonded para-substituted pyridine⋯(X2/XY/HX) complexes (original) (raw)
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International Journal of Quantum Chemistry, 2014
Optimal structures, electronic and thermodynamic properties of the title complexes are presented. The stability of the hydrogen bonded systems is enhanced by the increasing dipole moments whereas in the halogen bonded systems it is also affected by the atom size in the diatomics. The consecutive addition of fluorine atoms to the pyridine moiety results in the decrease of the interaction energy for both types of the investigated bonds. The substitution on the meta sites in pyridine leads to more stable complexes than the substitution in the ortho position. The role of substitution on electric polarization and electrostatic forces is estimated by the symmetry-adapted perturbation theory energy decomposition. The predicted Gibbs free energies of the complexes of mono fluorinated pyridines with HCl, HF, and ClF are from 212 to 222 kJ mol 21 at 200 K. The possible experimental identification of the complexes with respect to the vibrational modes is discussed. V
Symmetry
The DFT calculations have been performed on a series of two-element complexes formed by substituted 2,6-diaminopyridine (R−PDA) and pyridine (R−Pyr) with X−CY3 molecules (where X = Cl, Br and Y = H, F). The primary aim of this study was to examine the intermolecular hydrogen and halogen bonds in the condition of their mutual coexistence. Symmetry/antisymmetry of the interrelation between three individual interactions is addressed. It appears that halogen bonds play the main role in the stabilization of the structures of the selected systems. However, the occurrence of one or two hydrogen bonds was associated with the favourable geometry of the complexes. Moreover, the impact of different substituent groups attached in the para position to the aromatic ring of the 2,6-diaminopyridine and pyridine on the character of the intermolecular hydrogen and halogen bonds was examined. The results indicate that the presence of electron-donating substituents strengthens the bonds. In turn, the p...
Jordan Journal of Chemistry, 2015
NMR properties of the hydrogen bond and CH- interactions in the FH…Pyridine┴Xbenzene complexes (where ┴ denotes CH- interaction and X = NH2, OH, H, Cl, Br, and NO) have been investigated at the PBE1KCIS/6-311++G(d,p) level of theory. In addition to geometrical parameters, binding energies and Hammett constants, results of natural bond orbital (NBO) analyses are in good relationship with calculated NMR data (particularly with the twobond 19 F 15 N spin-spin coupling constant 2h JF-N). Also, the relation between cooperativity energy (Ecoop) and NMR data was considered. The results of this study led to better understanding of the NMR properties of the hydrogen bond and CH-p interactions in the complexes involved.
Physical Chemistry Chemical Physics, 2014
In this work, we have investigated a subtle competition between a very weak np Ar * interaction and a very strong hydrogen bond (N-HÁ Á ÁN) interaction present in the complexes of 7-azaindole with a series of 2,6-substituted fluoropyridines and observed how the weak interaction modulates the overall structural motif of these complexes in the presence of the strong interaction. We have studied the structures and binding energies of these complexes using MP2 as well as dispersion-corrected DFT calculations. It has been found that the strength of the N-HÁ Á ÁN interaction in these complexes decreases with increasing fluorination in the fluoropyridine ring while the proximity between the nitrogen atom in 7-azaindole and the aromatic ring of fluoropyridine increases through np Ar * interaction.
The kinetics of the hydration reaction on trans-[Pt(NH 3) 2 (pyrX)Cl] + (pyr = pyridine) complexes (X = OH − , Cl − , F − , Br − , NO 2 − , NH 2 , SH − , CH 3 , CCH, and DMA) was studied by density functional theory calculations in the gas phase and in water solution described by the implicit polarizable continuum model method. All possible positions ortho, meta, and para of the substituent X in the pyridine ring were considered. The substitution of the pyr ligand by electron-donating X's led to the strengthening of the Pt−N1(pyrX) (Pt− N pyrX) bond and the weakening of the trans Pt−Cl or Pt−O w bonds. The electronwithdrawing X's have exactly the opposite effect. The strengths of these bonds can be predicted from the basicity of sigma electrons on the N pyrX atom determined on the isolated pyrX ligand. As the pyrX ring was oriented perpendicularly with respect to the plane of the complex, the nature of the X•••Cl electrostatic interaction was the decisive factor for the transition-state (TS) stabilization which resulted in the highest selectivity of ortho-substituted systems with respect to the reaction rate. Because of a smaller size of X's, the steric effects influenced less importantly the values of activation Gibbs energies ΔG ⧧ but caused geometry changes such as the elongation of the Pt−N pyrX bonds. Substitution in the meta position led to the highest ΔG ⧧ values for most of the X's. The changes of ΔG ⧧ because of electronic effects were the same in the gas phase and the water solvent. However, as the water solvent dampened electrostatic interactions, 2200 and 150 times differences in the reaction rate were observed between the most and the least reactive mono-substituted complexes in the gas phase and the water solvent, respectively. An additional NO 2 substitution of the pyrNO 2 ligand further decelerated the rate of the hydration reaction, but on the other hand, the poly-NH 2 complexes were no more reactive than the fastest o-NH 2 system. In the gas phase, the poly-X complexes showed the additivity of the substituent effects with respect to the Pt−ligand bond strengths and the ligand charges.
Geometrical Features of Hydrogen Bonded Complexes Involving Sterically Hindered Pyridines
The Journal of Physical Chemistry A, 2006
The ability of strongly sterically hindered pyridines to form hydrogen bonded complexes was inspected using low-temperature 1 H and 15 N NMR spectroscopy in a liquefied Freon mixture. The proton acceptors were 2,6-di(tert-butyl)-4-methyl-and 2,6-di(tert-butyl)-4-diethylaminopyridine; the proton donors were hydrogen tetrafluoroborate, hydrogen chloride, and hydrogen fluoride. The presence of the tert-butyl groups in the ortho positions dramatically perturbed the geometry of the forming hydrogen bonds. As revealed by experiment, the studied crowded pyridines could form hydrogen bonded complexes with proton donors exclusively through their protonation. Even the strongest small proton acceptor, anion F-, could not be received by the protonated base. Instead, the simplest hydrogen bonded complex involved the [FHF]anion. This complex was characterized by the shortest possible N‚‚‚F distance of about 2.8 Å. Because the ortho tert-butyl groups did not prevent the hydrogen bond interaction between the protonated center and the anion completely, an increase of the pyridine basicity caused a further shortening of the N-H distance and a weakening of the hydrogen bond to the counterion. * To whom correspondence should be addressed. shender@ chemie.fu-berlin.de.
The features of electron density in the complexes of substituted pyridines have been studied with a special attention to the NÁ Á ÁI halogen bonding. The source function indicates that the major contribution to the electron density at the bond critical point of NÁ Á ÁI interaction goes from the basin of iodine atom. The delocalization indices for halogen bond NÁ Á ÁI quantitatively correlate with the sum of atomic sources of iodine and nitrogen. This finding allows estimating the delocalization indices directly from the electron density. The delocalization indices of halogen bond are well correlated with the basicity pK BI2 according to the diiodine basicity scale.
Chemical Physics Letters, 2019
Complexes between para-substituted pyridine and SeH 2 have been investigated at the MP2/aug-cc-pVTZ level. Various electron donating and withdrawing substituents (-NH 2 ,-OH,-CH 3 ,-H,-F,-Cl,-CN, and-NO 2) are chosen in order to characterize their influence on Se-H⋯N intermolecular hydrogen-bonding interaction. The electron donating substituents lead to an increase of the stabilization energy along with elongation in the Se-H bond length and redshift in Se-H stretching frequency. Conventional electronic substitution effect has been observed on various hydrogen-bond parameters, such as, stabilization energy, change in Se-H bond length and stretching frequency, charge transfer, bond order, electron density at hydrogen-bond critical point.
A theoretical study of hydrogen complexes of the XH-π type between propyne and HF, HCL or HCN
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2006
The present manuscript reports a systematic investigation of the basis set dependence of some properties of hydrogen-bonded (type) complexes formed by propyne and a HX molecule, where X = F, Cl and CN. The calculations have been performed at Hartree-Fock, MP2 and B3LYP levels. Geometries, H-bond energies and vibrational have been considered. The more pronounced effects on the structural parameters of the isolated molecules, as a result of complexation, are verified on R C C and HX bond lengths. As compared to double-(6-31G **), triple-(6-311G **) basis set leads to an increase of R C C bond distance, at all three computational levels. In the case where diffuse functions are added to both hydrogen and 'heavy' atoms, the effect is more pronounced. The propyne-HX structural parameters are quite similar to the corresponding parameters of acetylene-HX complexes, at all levels. The largest difference is obtained for hydrogen bond distance, R H , with a smaller value for propyne-HX complex, indicating a stronger bond. Concerning the electronic properties, the results yield the following ordering for H-bond energies, E: propyne• • •HF > propyne• • •HCl > propyne• • •HCN. It is also important to point out that the inclusion of BSSE and zero-point energies (ZPE) corrections cause significant changes on E. The smaller effect of ZPE is obtained for propyne• • •HCN at HF/6-311++G ** level, while the greatest difference is obtained at MP2/6-31G ** level for propyne• • •HF system. Concerning the IR vibrational it was obtained that larger shift can be associated with stronger hydrogen bonds. The more pronounced effect on the normal modes of the isolated molecule after the complexation is obtained for H X stretching frequency, which is shifted downward.
Molecules
In the present work, a number of R–X⋯NH3 (X = Cl, Br, and I) halogen bonded systems were theoretical studied by means of DFT calculations performed at the ωB97XD/6-31+G(d,p) level of theory in order to get insights on the effect of the electron-donating or electron-withdrawing character of the different R substituent groups (R = halogen, methyl, partially fluorinated methyl, perfluoro-methyl, ethyl, vinyl, and acetyl) on the stability of the halogen bond. The results indicate that the relative stability of the halogen bond follows the Cl < Br < I trend considering the same R substituent whereas the more electron-withdrawing character of the R substituent the more stable the halogen bond. Refinement of the latter results, performed at the MP2/6-31+G(d,p) level showed that the DFT and the MP2 binding energies correlate remarkably well, suggesting that the Grimme’s type dispersion-corrected functional produces reasonable structural and energetic features of halogen bond systems. ...