Experimental characterization of C-X···Y-C (X = Br, I; Y = F, Cl) halogen-halogen bonds.

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On the Experimental Characterization of C–X…Y–C (X = Br, I; Y = F, Cl) Halogen – Halogen Halogen Bonds Dieter Hauchecorne, and Wouter A. Herrebout J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/jp4077323 • Publication Date (Web): 15 Oct 2013 Downloaded from http://pubs.acs.org on October 29, 2013

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The Journal of Physical Chemistry

On the Experimental Characterization of C–X…Y–C (X = Br, I; Y = F, Cl) Halogen – Halogen Halogen Bonds Dieter Hauchecorne, Wouter A. Herrebout* Department of Chemistry, University of Antwerp Groenenborgerlaan 171, 2020 Antwerp, Belgium Keywords Vibrational spectroscopy; cryosolutions; blue shifting; Van der Waals molecules; Ab initio calculations

Abstract Using FTIR and Raman spectroscopy, the formation of halogen bonded complexes of the trifluorohalomethanes CF3Cl, CF3Br and CF3I with the halomethanes CH3F and CH3Cl and the haloethanes C2H5F and C2H5Cl dissolved in liquid krypton have been investigated. For CF3Br and CF3I, evidence was found for the formation of C–X…F and C–X…Cl halogen bonded 1:1 complexes. Using spectra recorded at different temperatures, the complexation enthalpies for the complexes were determined to be -7.0(3) kJ mol-1 for CF3Br.CH3F, -7.6(1) kJ mol-1 for 1 ACS Paragon Plus Environment


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CF3I.CH3F, -5.9(2) kJ mol-1 for CF3Br.CH3Cl, -8.3(3) kJ mol-1 for CF3I.CH3Cl, -7.1(1) kJ mol-1 for CF3Br.C2H5F, -8.7(2) kJ mol-1 for CF3I.C2H5F, -6.5(2) kJ mol-1 for CF3Br.C2H5Cl and -8.8(3) kJ mol-1 for CF3I.C2H5Cl. For all halogen bonded complexes with a fluorine-electron donor, a blue shift ranging from +0.6 to +1.5 cm-1 was observed for the C–X stretching mode. The results from the cyrospectroscopic study are compared with ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level.

1. Introduction Halogen bonding, or the non-covalent interaction between a polarized halogen atom and an electron rich region in a Lewis base, has been the focus of an increasing number of studies over the past few years. This boost is related to the growing number of applications involving halogen bonds, ranging from crystal engineering1-5 to separation techniques6 and biochemical processes.7-12 The electron-donor in these applications is very often a lone-pair of a heteroatom such as nitrogen, oxygen or sulphur but also applications with a π-system as the electron-donor occur, although these are less common. An interesting, yet currently undervalued, subclass of halogen bonding is the C–X...Y interaction, with X and Y a halogen atom. This type of halogen bond plays an important role as a secondary interaction in crystal engineering. Based on the C–X…Y bond angle, θ1, and the C–Y…X bond angle, θ2, Desiraju13 suggested two types of the C–X…Y halogen bond: Type I consists of interactions where θ1 = θ2 and Type II features the interactions with θ1 ≈ 180 degrees and θ2 ≈ 90 degrees. It is clear that these Types influence the obtained supramolecular structure which has its repercussion on the formed compound and its physical properties.14-16 Consequently, it is essential to know to what Type a certain combination of X and Y belongs as to maximize the potential applicability of the formed crystal structure. Interestingly, a recent study has shown that halogen…halogen interactions

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can occur both inter- and intramolecular, although some debate still remains whether the latter should be considered as a proper bond.17 We have recently initiated an infrared and Raman spectroscopic study on halogen bonded complexes in cryogenic solutions, supported by various ab initio calculations. The halogen bond-donors used in this study are the trifluorohalomethanes CF3X, with X = Cl, Br or I as the electron-acceptor. The electrondonors studied so far are nitrogen,18 oxygen,19 sulphur20 and both the aromatic21 and non-aromatic22 πsystems. To obtain more information about the C–X...Y halogen bond, this study expands the set of electron-donors with the fluorine and chlorine atoms in fluoromethane (CH3F), fluoroethane (C2H5F), chloromethane (CH3Cl) and chloroethane (C2H5Cl). The choice for these atoms is triggered by their use in previous studies on hydrogen bonding and the proven solubility of the compounds in liquid noble gases.23 The study of the halomethane and -ethane species also allows to clarify the differences in the electron donating capacity of the methyl and ethyl group.

2. Experimental and computational details The samples of fluoroethane (C2H5F, 97+%), chloromethane (CH3Cl, 99.5+%), chloroethane (C2H5Cl, 99.7%) and trifluoroiodomethane (CF3I, 99%) were purchased from Sigma Aldrich. The samples of fluoromethane (CH3F, 98%), chlorotrifluoromethane (CF3Cl, 99%) and bromotrifluoromethane (CF3Br, 99%) were obtained from ABCR, Praxair and Pfaltz & Bauer, respectively. All samples were used without further purification. The krypton used had a stated purity of 99.9995% and was supplied by Air Liquide. Infrared spectra were recorded on a Bruker IFS 66v Fourier transform spectrometer. For the midinfrared spectra, a Globar source was used in combination with a Ge/KBr beam splitter and a LN2-cooled broad band MCT detector. For the far-infrared spectra, a six micron Mylar beam splitter and a liquid Hecooled bolometer was used. The interferograms were averaged over 500 scans, Blackman-Harris threeterm apodized and Fourier transformed to yield spectra with a resolution of 0.5 cm-1. The experimental



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set-up used to investigate the solutions in liquid noble gases has been described before.24 A liquid cell equipped with wedged Si windows with a path length of 1 cm was used to record the spectra. Raman spectra were recorded using a Trivista 557 spectrometer consisting of a double f = 50 cm monochromator equipped with a 300/1500/2000 lines mm-1 gratings and a f = 70 cm spectrograph equipped with a 500/1800/2400 lines mm-1 gratings and a back-end illuminated LN2 cooled CCD detector. The 514.5 nm line of a Spectra-Physics argon ion laser was used for Raman excitation, and the power of the incident laser beam was set to 0.8 W. Frequencies were calibrated using Ne emission lines, and are expected to be accurate to 0.2 – 0.5 cm-1. The resolution selected resulted in full widths at halfheight of the Ne calibration lines that varied between 0.5 and 0.6 cm-1. The experimental set-up with which the solutions were investigated has been described before.25 A home-built liquid cell equipped with four quartz windows at right angles was used to record the spectra. Geometries and harmonic vibrational frequencies of monomers and complexes were obtained from ab initio calculations at the MP2/aug-cc-pVDZ(-PP) level. Corrections for BSSE were accounted for using CP-corrected gradient techniques.26 The standard aug-cc-pVDZ basis set was used for hydrogen, carbon, fluorine and chlorine atoms. For bromine and iodine atoms, the aug-cc-pVDZ-PP basis set was used, which includes small-core energy-consistent relativistic pseudopotentials (PP)27 to account for relativistic effects. The combination of these two basis sets has been shown to result in a satisfactory prediction of halogen bonded complexes.20-22 All ab initio calculations were made using Gaussian03.28 Solvation Gibbs energies ∆solG were obtained from Monte Carlo Free Energy Perturbation (MC-FEP) calculations, using a locally modified version of BOSS 4.1,29 as described before.30 For each species, the Gibbs energies of solvation in liquid krypton were estimated at 6 different temperatures, varying from 119 to 179 K, at a pressure of 28 bar. Subsequently, the enthalpy of solvation ∆solH was extracted using the expression ∆solH = ∆solG + T∆solS with the entropy of solvation ∆solS = – ( ∂ ∆solG/ ∂ T)p.31

3. Results and discussion 4 ACS Paragon Plus Environment

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3.1

Ab initio calculations, statistical thermodynamics and Monte Carlo – Free energy

perturbation simulation Quantum chemical structures and harmonic frequencies for the complexes of CF3X with CH3Y were derived at the MP2/aug-cc-pVDZ(-PP) level. The structural parameters of the monomers and those of the complexes are summarized in Tables 1 and 2. The resulting equilibrium geometries, of C1 symmetry, are shown schematically in Figure 1. The complexes of CF3X with CH3Y show a near linear C–X…Y halogen bond. The C–X…Y bond angle, θ1, is observed to increase from 165.4 degrees for CF3Cl.CH3Cl to 174.1 degrees for CF3I.CH3F. The C–Y…X bond angle, θ2, is observed to increase from 86.2 degrees for CF3Br.CH3Cl to 118.2 degrees for CF3I.CH3F. Based on the convention proposed by Desiraju13 it is clear that the studied complexes belong to Type II. The X…F interatomic distance in the CH3F complexes is predicted close to 3.02 Å for the CF3Cl and CF3Br complex and 3.11 Å for the CF3I complex. For the CH3Cl complexes, the X…Cl distances are 3.47 Å for the CF3Br complex, 3.49 Å for the CF3Cl complex and 3.54 Å for the CF3I complex. These values are all significantly smaller than the sum of the van der Waals radii for X and Y, which increase from 3.15 Å for the CF3Cl.CH3F complex to 3.95 Å for the CF3I.CH3Cl complex. The ratio of the X…F halogen bond length to the sum of the van der Waals radii equals 0.96 for the CF3Cl.CH3F complex, 0.91 for the CF3Br.CH3F complex and 0.89 for the CF3I.CH3F complex. Similar ratios are found for the CH3Cl complexes, i.e. 0.97 for the CF3Cl complex, 0.92 for the CF3Br complex and 0.90 for the CF3I complex.

The trends reflect the increasing stability of the complexes, the MP2/aug-cc-pVDZ(-PP)

complexation energies being -6.4 kJ mol-1 for CF3Cl.CH3F, -8.7 kJ mol-1 for CF3Br.CH3F, -10.8 kJ mol-1 for CF3I.CH3F, -6.6 kJ mol-1 for CF3Cl.CH3Cl, -9.1 kJ mol-1 for CF3Br.CH3Cl and -11.4 kJ mol-1 for CF3I.CH3Cl. These values are also in line with the increase in size and depth of the respective σ-holes on



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the non-bonded side of the unique halogen atom in CF3Cl, CF3Br and CF3I.32 The ab initio complexation energies thus indicate that the complexes of CH3Cl are stronger than those with CH3F, while the ratio of the X…Y halogen bond length to the sum of the van der Waals radii predicts the opposite. Similar results were obtained for the complexes of CF3X with C2H5Y. The structural parameters of the monomers and those of the complexes are summarized in Tables S1 and S2 of the Supporting information. The resulting equilibrium geometries, of C1 symmetry for all complexes, are shown schematically in Figure S1 of the Supporting information. It should be noted that the gauche orientation, with the C–C– Y…X torsion angle close to 80 degrees, was found to be the only stable structure for these complexes. The trans isomer orientation, with the C–C–Y…X torsion angle close to 180 degrees, produced a negative vibrational eigenvalue and was thus not studied further. Similar to the complexes with CH3Y, the complexes with C2H5Y also belong to Type II, as defined above. Analogous results for the X…Y interatomic distances as in the CH3Y complexes are found for the C2H5Y complexes, reflecting the increasing stability of the complexes, the MP2/aug-cc-pVDZ(-PP) complexation energies being -7.8 kJ mol-1 for CF3Cl.C2H5F, -10.4 kJ mol-1 for CF3Br.C2H5F, -12.8 kJ mol-1 for CF3I.C2H5F, -8.2 kJ mol-1 for CF3Cl.C2H5Cl, -10.8 kJ mol-1 for CF3Br.C2H5Cl and -13.4 kJ mol-1 for CF3I.C2H5Cl. These values are also in line with the increase in size and depth of the respective σ-holes on the non-bonded side of the unique halogen atom in CF3Cl, CF3Br and CF3I.32 Similar trends as those found for the CH3Y complexes are observed for the C2H5Y complexes. The latter complexes are generally stronger than the former, in agreement with the more pronounced inductive effect of the ethyl group in C2H5Y. At this point it is also of interest to compare the structures of the present complexes with that of the C– H hydrogen bonded complex of trifluoromethane with CH3F.23 Several possible geometries were found for this complex with varying C–H...F bond angles ranging from 118.2 to 180.0 degrees. The geometry


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with the former bond angle was calculated to be the most stable one. In this complex, the C–H...F interaction is accompanied by two additional interactions between two of the fluorine atoms with two hydrogen atoms in the Lewis base, creating a ring like structure. These extra short contacts also explain the significant tilting away from linearity observed in the complex. The complexation energy of the most stable structure was calculated at -11.7 kJ mol-1, which suggests that the CF3H complex is stronger than the CF3X complexes. Bearing previous results in mind, this is somewhat surprising. On closer inspection however, the extra stability of the hydrogen bonded complex can be explained by the presence of the two additional F...H hydrogen bonds and the resulting cooperative effect. The complexation energy for only one hydrogen bond should thus be less than the calculated -11.7 kJ mol-1. It is also worth nothing that, although the halogen bonded complexes studies are calculated to be very weak, and although other type of complexes including, e.g. a F3C-X…H-CH2X interaction can be envisaged, no such type of complexes could be localized on the potential energy surfaces. Ab initio vibrational frequencies and infrared intensities obtained for the monomers and for the halogen bonded complexes are given in Tables S3 to S14 of the Supporting information. To allow comparison of the ab initio results with the experimental stabilities, corrections for solvent interactions and thermal influences were calculated. The resulting values of the standard complexation enthalpy are -3.3(2) kJ mol-1 for CF3Cl.CH3F, -7.6(2) kJ mol-1 for CF3Br.CH3F, -9.7(2) kJ mol-1 for CF3I.CH3F, -0.4(2) kJ mol-1 for CF3Cl.CH3Cl, -6.3(2) kJ mol-1 for CF3Br.CH3Cl and -8.8(2) kJ mol-1 for CF3I.CH3Cl. These complexation enthalpies suggest that, in solution, the CH3F complexes are stronger than those with CH3Cl. A similar trend can be observed for the C2H5Y complexes, with calculated standard complexation enthalpies of -5.7(2) kJ mol-1 for CF3Cl.C2H5F, -7.6(2) kJ mol-1 for CF3Br.C2H5F, -10.0(3) kJ mol-1 for CF3I.C2H5F, -5.1(2) kJ mol-1 for CF3Cl.C2H5Cl, -7.5(3) kJ mol-1 for CF3Br.C2H5Cl and -10.4(4) kJ mol-1 for CF3I.C2H5Cl.



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To gain more insight into the driving force behind the C–X...Y halogen bond, symmetry adapted perturbation theory (SAPT)33 has been applied on the CH3Y complexes, calculated at the MP2 level. SAPT analysis allows the separation of the interaction energies in commonly understood physical quantities:34 Eint = E pol1 + Eex1 + Eind 2 + E ex − ind 2 + E disp 2 + Eex − disp 2

(10.1)

E ( elec.) = E pol1 with

E ( ind .) = Eind 2 + Eex −ind 2 E ( disp.) = Edisp 2 + Eex − disp 2

(10.2)

E ( exch.) = Eex1 referring to the electrostatic, induction, dispersion and exchange contributions, respectively, to the overall interaction energy. The results of the SAPT analyses, carried out using Molpro2009,35 obtained for the CH3Y complexes are listed in Table 3. It can be seen that for all complexes the component contributing most to the interaction energy is the electrostatic one. However, its relative contribution to the total energy decreases when going from CH3F to CH3Cl, favouring the dispersion and induction contributions. It is also clear that, for each of the contributions, the absolute values increase from CF3Cl to CF3I. This trend is traced back to the greater polarizability of the iodine atom, resulting in a larger and deeper σ-hole and, consequently, a larger penetration of the respective halogen-electron donor. The total interaction energies suggest that, for CF3Cl and CF3Br, the complex with CH3F is stronger than the one with CH3Cl, in agreement with the complexation enthalpies and the ratio of the X...Y halogen bond length to the sum of the van der Waals radii. For the CF3I complexes on the other hand, the complex with CH3Cl is stronger than the one with CH3F, in agreement with the MP2 complexation energies. These trends obviously remain valid when the SAPT interaction energies are transformed into complexation enthalpies. Similar conclusions can be drawn for the C2H5Y complexes.


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It should also be noticed that the difference between the energies derived from the SAPT analysis differ from those derived from the MP2 calculations.

This is probably due to the fact that the SAPT

calculations, in contrast to the MP2 calculations, are BSSE free.

Furthermore, errors due to

approximations in the SAPT analysis can occur: only first and second order contributions to the interaction energy are accounted for, while only the wave functions obtained at the Hartree–Fock level are used.36

3.2 Vibrational spectra Vibrational spectra of different series of mixtures of CF3X and CH3Y or C2H5Y dissolved in liquid krypton were investigated.

For the infrared spectra, mole fractions varying between 7.5×10-5 and

2.0×10-2 of the halomethanes, between 1.2×10-3 and 1.5×10-2 of CH3Y, and between 1.1×10-3 and 1.3×10-2 of C2H5Y were used. For the Raman spectra, the mole fractions varied between 9.8×10-4 and 4.7×10-3 for all monomers. For mixed solutions of CF3Cl, no features suggesting the formation of a complex were detected. The obvious conclusion is that the complex is too weak to be observed. Apart from the monomer bands in the spectra of the mixed solutions of CF3X and CH3Y or C2H5Y, new bands caused by 1:1 complexes were observed for a variety of modes localized in the CF3X and CH3Y or C2H5Y moieties. The observed frequencies, their assignments and their complexation shifts are collected in Tables 4 to 7. In Figure 2A, the CF3 stretching region of a solution containing mole fractions of 3.2×10-4 of CF3Br and 1.3×10-2 of CH3F dissolved in liquid krypton, trace a, is compared with the spectra of the monomers in traces b and c, respectively. The new bands in the spectra of the mixture, marked with an asterisk, are assigned to the 1:1 complex. It can be seen that weak bands, assigned as the antisymmetric, ν 4CF Br and 3

symmetric, ν 1CF Br , stretching modes in the complex, are detected at 1191.5 and 1079.7 cm-1. The 3

experimental shifts for these bands, -6.6 cm-1 for ν 4CF Br and +4.5 cm-1 for ν 1CF Br , compare favourably with 3


3


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the ab initio values of -9.2 and +6.5 cm-1. Similar, but more pronounced, complex bands can be observed in the top trace in Figure 2B, where the corresponding region of a solution containing mole fractions of 9.4×10-5 of CF3I and 5.6×10-3 of CH3F is given. The complex bands assigned to ν 4CF I and ν 1CF I are 3

3

observed at 1166.8 and 1072.9 cm-1. The experimental complexation shifts, -8.8 and +5.5 cm-1, agree nicely with the theoretical values of -9.8 and +8.5 cm-1. Even though the monomer concentrations in panel B are about three times smaller as those in panel A, the complex bands in the former panel are slightly more pronounced, so that from the relative intensities it is inferred that the complex with CF3I is more stable than that with CF3Br. In order to visualise the differences between the four Lewis bases, Figure 3 depicts the infrared spectra of the CF3 stretching region for the complexes of CF3I with CH3F (panel A), C2H5F (panel B), CH3Cl (panel C) and C2H5Cl (panel D) observed in liquid krypton. In each panel, trace a gives the spectrum of the mixed solution, while traces b and c were recorded from a solution in which only CF3I or the Lewis base was dissolved in liquid krypton, respectively. Complex bands for the 1:1 complex are marked with an asterisk. The spectra in Figure 3A are the same as those depicted in Figure 2B and thus need no further discussion. Similar, but more pronounced complex bands can be observed in the top trace of Figure 3B, where the corresponding region of a solution containing mole fractions of 9.4×10-5 of CF3I and 2.1×10-3 of C2H5F is given. It can be seen that this region is more complicated by the presence of three relatively intense C2H5F monomer bands, located at 1169.4, 1104.7 and 1062.8 cm-1. The former two are assigned to ν 16C H 2

5F

and ν 8C

2H5F

, while the latter is due to an overtone or combination band. Except for a more

difficult subtraction, the C2H5F bands barely influence the interpretation of this spectral region. The complex band observed at 1165.3 cm-1 can either be assigned to ν 16C H 2

5F

or to ν 4CF I . The ab initio relative 3

intensities for these complex bands, 3.9 and 450.1 km mol-1, respectively, are such that with high certainty the 1165.3 cm-1 band should be assigned to ν 4CF I , as expected from panel A. The other complex band, 3

observed at 1073.5 cm-1 is assigned to ν 1CF I . The observed complexation shifts, -10.3 and +6.1 cm-1, 3


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agree nicely with the theoretical values of -10.7 and +10.8 cm-1. The differences in complexation shifts and relative intensities between panels A and B are a clear indication of the higher stability of the C2H5F complex. Figure 3C shows the spectra of a solution containing mole fractions of 7.5×10-5 of CF3I and 3.8×10-3 of CH3Cl. In this panel, the only complex band observed is ν 4CF I , at 1168.5 cm-1. The experimental 3

complexation shift of -7.1 cm-1 agrees nicely with the theoretical values of -7.5 cm-1. Because of the low concentration of CH3Cl, the complex band due to ν 1CF I remains undetected in this panel. By using higher 3

concentrations of both monomers, this complex band was seen at 1070.8 cm-1.

The resulting

complexation shift of +3.4 cm-1 agrees nicely with the calculated shift of +5.2 cm-1. Finally, the spectra of a solution containing mole fractions of 7.5×10-5 of CF3I and 1.9×10-3 of C2H5Cl are shown in Figure 3D. Even though the Lewis base concentration in this panel is only half the concentration used in panel C, both ν 4CF I and ν 1CF I are present here. 3

3

They give rise to absorptions at 1167.4 and 1070.5 cm-1,

respectively. The experimental complexation shifts, -8.2 and +3.1 cm-1, agree well with the calculated values of -7.9 and +5.0 cm-1. The differences in complexation shifts and relative intensities between panels C and D are a clear indication of the higher stability of the C2H5Cl complex. Infrared spectra in the C–X stretching regions for the C–X...F complexes are given in Figure 4. In each panel, trace a gives the spectrum of the mixed solution, trace b was recorded from a solution in which only CF3X was dissolved in liquid krypton. Trace c shows the spectrum of the 1:1 complex, obtained by subtracting trace b from trace a. Complex bands for the 1:1 complex are marked with an asterisk. The infrared spectra for the CF3Br.CH3F and CF3Br.C2H5F complexes are shown in panels A and B, respectively. Trace a in panel A clearly shows the presence of a 79Br/81Br isotopic doublet, with maxima at 353.4 and 351.6 cm-1. This doublet is assigned as ν 3CF Br in the complex and is blue shifted by +1.3 3

cm-1 from their frequencies in the monomer. A similar blue shift can be seen in trace a of panel B, the 79Br/81Br

isotopic doublet show maxima at 353.6 and 351.7 cm-1, leading to a blue shift of +1.5 cm-1.



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These results are in agreement with the calculated complexation shifts of +1.0 and +0.7 cm-1, respectively. The weak CF3Br monomer bands in trace b of both panels are not found back in trace a, which, in view of the magnification by a factor of 5 applied to trace b, is not surprising. The infrared spectra for the CF3I analogues are shown in panels C and D, respectively. The ν 3CF I complex band in panels C and D can be 3

seen to blue shift by +0.8 and +0.6 cm-1, respectively. Several theoretical studies37-38 comparing the properties of C–H...Y hydrogen bonds and C–X...Y halogen bonds have drawn attention to the fact that blue shifts for the C–X stretching vibration are possible. However, Wang and Hobza only focussed on the complexes where X = Cl or Br since “the iodoperfluoroalkanes are always involved in the red shifting halogen bond”.38 To date, experimental evidence for such a blue shift was indeed not found. This study, however, provides the first experimental evidence for a blue shifting halogen bond involving an iodine containing Lewis acid and thus refutes Wang and Hobza’s statement. Furthermore, a blue shift was also observed for the bromine containing Lewis acid. In principle and in analogy to what was done for the blue shifting hydrogen bonds,39 an analysis of the possible origins of that shift in terms of the Buckingham model40 could be made. However, the largest observed shift upon complexation is a mere +1.0 cm-1. This, and the fact that ν 3CF X is not a 3

pure C–X stretching mode but is coupled to other internal coordinates, makes that such an analysis must be judged futile. The analysis was, therefore, not pursued. Infrared spectra in the C–X stretching regions for the C–X...Cl complexes are given in Figure 5. In each panel, trace a gives the spectrum of the mixed solution, traces b and c were recorded from a solution in which only CF3X or C2H5Cl was dissolved in liquid krypton. Trace d shows the spectrum of the 1:1 complex, obtained by subtracting traces b and c from trace a. Complex bands for the 1:1 complex are marked with an asterisk. The infrared spectra for the CF3Br.CH3Cl and CF3Br.C2H5Cl complexes are shown in panels A and B, respectively. Trace a in panel A clearly shows the presence of a 79Br/81Br isotopic doublet, with maxima at 352.0 and 350.1 cm-1. This doublet is assigned as ν 3CF Br in the complex 3


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and is red shifted by -0.1 cm-1 from their frequencies in the monomer. A similar red shift can be seen in trace a of panel B, the 79Br/81Br isotopic doublet show maxima at 351.9 and 350.0 cm-1, leading to a red shift of -0.2 cm-1. These results are in agreement with the calculated complexation shifts of -1.1 and -1.2 cm-1, respectively. The weak CF3Br monomer bands in trace b of both panels are not found back in trace a, which, in view of the magnification by a factor of 5 applied to trace b, is not surprising. The infrared spectra for the CF3I analogues are shown in panels C and D, respectively. The ν 3CF I complex band in 3

panels C and D can be seen to red shift by -1.0 and -1.2 cm-1, respectively. Several examples of complex bands due to C2H5Y modes are shown in Figure 6. The C–C stretching vibration of a CF3I/C2H5Cl, a CF3Br/C2H5F and a CF3I/C2H5F mixture are shown in panels A, B and C, respectively. In addition, the C–Cl stretching vibration of a CF3I/C2H5Cl mixture is shown in panel D. In each panel, trace a gives the spectrum of the mixed solution, while traces b and c were recorded from a solution in which only C2H5Y or CF3X was dissolved in liquid krypton. Complex bands for the 1:1 complex are marked with an asterisk. Trace a in Figure 6A clearly shows that the C–C stretching mode in the CF3I.C2H5Cl complex is red shifted by -1.6 cm-1, while this mode in the C2H5F moiety leads to red shifts of -3.5 and -6.3 cm-1 in the CF3Br.C2H5F and CF3I.C2H5F complex, shown in panels B and C, respectively. These results are in agreement with the calculated complexation shifts of -2.7, -5.8 and -8.3 cm-1, respectively. Trace a in Figure 6D, containing a mixture of CF3I and C2H5Cl dissolved in liquid krypton, clearly shows the presence of a 35Cl/37Cl isotopic doublet, with maxima at 661.7 and 657.1 cm-1. This doublet is assigned as the C–Cl stretching mode in the complex, red shifted by -8.6 cm-1 from their frequencies in the monomer. Similar complexation shifts are observed for the C–Cl and C–F stretching modes of the Lewis bases in the other complexes, but due to the overlap with several modes in the CF3X moiety, these bands are not discussed in detail.



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Page 14 of 38

3.3 Relative stability The relative stabilities for the 1:1 complexes were derived from temperature studies of different solutions using the van’t Hoff relation. This equation establishes a linear relation with a slope related to ∆H°(LKr)/R between the inverse temperature and the logarithm of the intensity product

I complex

(I

CF3 X

)

× I Lewisbase in which I complex , I CF X and I Lewis base each represent the sum of the intensities of 3

several bands of the monomers and of the complex. Typical van’t Hoff plots obtained for the complexes, and the resulting linear regression lines are shown in Figures 7 and S2 of the Supporting information. The average complexation enthalpies, obtained by analyzing data for a series of solutions, are -7.0(3) kJ mol-1 for CF3Br.CH3F, -7.6(1) kJ mol-1 for CF3I.CH3F, -5.9(2) kJ mol-1 for CF3Br.CH3Cl, -8.3(3) kJ mol-1 for CF3I.CH3Cl, -7.1(1) kJ mol-1 for CF3Br.C2H5F, -8.7(2) kJ mol-1 for CF3I.C2H5F, -6.5(2) kJ mol-1 for CF3Br.C2H5Cl and -8.8(3) kJ mol-1 for CF3I.C2H5Cl. These results in the first place confirm the stability order between the CF3Br and CF3I complexes and between the CH3Y and C2H5Y complexes discussed above on the basis of the ab initio complexation energies and the different spectral regions. Furthermore, the complexation enthalpies derived from the ab initio energies agree well with the experimental values. The results can also be compared with the ∆H°

value of -7.2(5) kJ mol-1 measured by Rutkowski et al.23 for CF3H.CD3F in liquid krypton. It is clear that this ∆H° value indicates that the strength of the CF3H complex is comparable to the CF3I complex. The results also suggest that the C–Br...F halogen bonds are generally stronger than their C–Br...Cl counterparts, while the opposite trend is observed for the complexes with CF3I. As stated in section 3.1, the ab initio complexation energies indicate that the complexes with a chlorine-electron donor are stronger than those with a fluorine-electron donor, while the calculated complexation enthalpies and the ratio of the X…Y halogen bond length to the sum of the van der Waals radii suggest the opposite. The SAPT analyses, however, are in full agreement with the experimental data.


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The complexation enthalpy of the halogen bonded complexes with a halogen-electron donor are found to have a comparable complexation enthalpy as the complexes involving a π-system21-22, ranging from 5.3(2) kJ mol-1 for CF3Br.ethene to -8.8(1) kJ mol-1 for CF3I.propene. However, the complexes with a halogen-electron donor are significantly weaker than the corresponding complexes with a heteroatomelectron donor,18-20 which can be as large as -28.7(1) kJ mol-1 for CF3I.trimethylamine.

4. Conclusions In this study, we have obtained experimental evidence for the formation of several C–X...F and C– X...Cl halogen bonds formed between CF3Br or CF3I and the halogen-electron donors CH3F, C2H5F, CH3Cl and C2H5Cl. The experimental results are supported by ab initio calculations of energies and vibrational frequencies. The experimental complexation enthalpies were found to be -7.0(3) kJ mol-1 for CF3Br.CH3F, -7.6(1) kJ mol-1 for CF3I.CH3F, -5.9(2) kJ mol-1 for CF3Br.CH3Cl, -8.3(3) kJ mol-1 for CF3I.CH3Cl, -7.1(1) kJ mol-1 for CF3Br.C2H5F, -8.7(2) kJ mol-1 for CF3I.C2H5F, -6.5(2) kJ mol-1 for CF3Br.C2H5Cl and -8.8(3) kJ mol-1 for CF3I.C2H5Cl and are in line with the theoretical calculations. For each of the halogen bonded complexes with a fluorine-electron donor, a blue shift for the C–X stretching mode was observed. To the best of our knowledge, this is the first time experimental evidence of a blue shifting halogen bond is provided.

ASSOCIATED CONTENT Supporting Information Equilibrium geometries and Van’t Hoff plots for the complexes with the haloethanes. Tables of calculated frequencies for all considered complexes. Complete author list of references 28 and 35. This information is available free of charge via the Internet at http://pubs.acs.org. 15 ACS Paragon Plus Environment


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Page 16 of 38

AUTHOR INFORMATION Corresponding Author Fax: (+32) 3 265 3220 E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The FWO-Vlaanderen is thanked for their assistance towards the purchase of spectroscopic equipment used in this study. The authors thank the Flemish Community for financial support through the special research fund (BOF). Financial support through the ‘Impulsfinanciering voor Grote Apparatuur’ and ‘Hercules Foundation’ allowing the purchase of the CalcUA/VSC supercomputing cluster is acknowledged. References 1.

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Conductors Based on Dibromo- and Diiodo-TSeFs with Magnetic and Non-Magnetic MX4 Counter Anions (M = Fe, Ga; X = Cl, Br) J. Mater. Chem. 2006, 16, 3381-3390. 3.

Sun, A.; Lauher, J. W.; Goroff, N. S. Preparation of Poly(diiododiacetylene), an Ordered

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C-H…Cl Intermolecular Interactions Involving Chlorine in Substituted 2-Chloroquinoline Derivatives J. Chem. Sci. 2010, 122, 677-685.

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Cl, Br and I) or Homo-Halogen (X…X, X = F, Cl, Br and I) Interactions in Substituted Benzanilides Cryst. Growth Des. 2011, 11, 1578-1598.

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Page 22 of 38

Figures

Figure 1. Equilibrium geometries for the complexes of CF3X (X = Cl, Br or I) with CH3F and CH3Cl calculated at the MP2/aug-cc-pVDZ(-PP) level.


Page 23 of 38

1200 Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1150

1100

A * *

a c b

B * *

a b c

1200

1150 1100 -1 Wavenumber/cm

Figure 2. Infrared spectra of the 1220 – 1050 cm-1 region for solutions of mixtures of CF3Br (A) and CF3I (B) with CH3F dissolved in LKr, at 123 K. Trace a represents the spectrum of the mixed solution, traces b and c are the spectra of the monomer CF3X and CH3F solution, respectively. The new bands appearing in the spectra of the mixture assigned to the 1:1 complex are marked with an asterisk (*).



1200 Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1150

Page 24 of 38

1100

A

a b c

*

*

B *

*

a b c

C

a b c

*

D

a

*

*

b c

1200

1150

1100 -1

Wavenumber/cm

Figure 3. Infrared spectra of the 1200 – 1050 cm-1 region for solutions of mixtures of CF3I with CH3F (A), C2H5F (B), CH3Cl (C) and C2H5Cl (D), dissolved in LKr, at 123 K. Trace a represents the spectrum of the mixed solution, traces b and c are the spectra of the monomer CF3X and CH3Y or C2H5Y solution, respectively. The new bands appearing in the spectra of the mixture assigned to the 1:1 complex are marked with an asterisk (*).


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Absorbance

Page 25 of 38

* *

A

C a

a b *

×5

b * *

c

D

B

a a

*

b c

b



Figure 4. Infrared spectra of the ν 3CF X region for solutions of mixtures of CF3Br (A and B) and 3

CF3I (C and D) with CH3F (A and C) and C2H5F (C and D) dissolved in LKr, at 123 K. Trace a represents the spectrum of the mixed solution, trace b is the spectrum of the monomer CF3X solution and trace c is the spectrum of the 1:1 complex, obtained by subtracting trace b from trace a. The new bands appearing in the spectra of the mixture assigned to the 1:1 complex are marked with an asterisk (*).


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Absorbance


A

Page 26 of 38

C

a

a b

b * *

*

d

d

D

B a

a

c

b ×5

b

*

* *

d

d



Figure 5. Infrared spectra of the ν 3CF X region for solutions of mixtures of CF3Br (A and B) and 3

CF3I (C and D) with CH3Cl (A and C) and C2H5Cl (C and D) dissolved in LKr, at 123 K. Trace a represents the spectrum of the mixed solution, traces b and c are the spectra of the monomer CF3X and C2H5Cl solution, respectively and trace d is the spectrum of the 1:1 complex, obtained by subtracting traces b and c from trace a. The new bands appearing in the spectra of the mixture assigned to the 1:1 complex are marked with an asterisk (*).


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Absorbance

Page 27 of 38

A

D

B

*

* *

a b c a

*

*

C a

a b

b c

c


b c



Figure 6. Infrared spectra of the C–C (A, B and C) and C–Cl (D) stretching regions for solutions of mixtures of CF3Br (B) and CF3I (A, C and D) with C2H5F (B and C) and C2H5Cl (A and D) dissolved in LKr, at 123 K. Trace a represents the spectrum of the mixed solution, while traces b and c are the spectra of the monomer C2H5Y and CF3X solution, respectively. The new bands appearing in the spectra of the mixture assigned to the 1:1 complex are marked with an asterisk (*).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 38

Figure 7. Van’t Hoff plots for the complexes of CF3Br (A and C) and CF3I (B and D) with CH3F (A and B) and CH3Cl (C and D) dissolved in LKr.


Page 29 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. MP2/aug-cc-pVDZ(-PP) bond lengths, in Å, and bond angles, in degrees, for the complexes of CF3Cl, CF3Br and CF3I with CH3F.a CF3Cl.CH3F

CF3Br.CH3F

CF3I.CH3F

CF3Xb rCF

1.3454

(0.0029)

1.3467

(0.0031)

1.3500

(0.0032)

rCX

1.7514

(-0.0042)

1.9099

(-0.0034)

2.1399

(-0.0029)

θXCF

110.61

(0.15)

110.74

(0.20)

110.96

(0.27)

rCH rCF

1.0976

(0.0001)

1.0975

(0.0000)

1.0974

(-0.0001)

1.4107

(0.0034)

1.4126

(0.0052)

1.4146

(0.0072)

θHCF

108.25

(-0.11)

108.20

(-0.16)

108.16

(-0.19)

CH3Fc

Intermolecular r X …F

3.03

3.02

3.11

sumvdW

3.15

3.30

3.50

θCX…F

169.86

172.73

174.06

θCF…X

109.41

114.05

118.19

a

The values in brackets are the changes induced by the complexation. The values for the van der Waals radii used to calculate sumvdW are 1.35 Å for F, 1.80 Å for Cl, 1.95 Å for Br and 2.15 Å for I.41 b

Structural data for the F-atom nearest to the CH3F moiety.

c

Structural data for the H-atom nearest to the CF3X moiety.



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Page 30 of 38

Table 2. MP2/aug-cc-pVDZ(-PP) bond lengths, in Å, and bond angles, in degrees, for the complexes of CF3Cl, CF3Br and CF3I with CH3Cl.a CF3Cl.CH3Cl

CF3Br.CH3Cl

CF3I.CH3Cl

CF3Xb rCF

1.3451

(0.0026)

1.3463

(0.0027)

1.3491

(0.0024)

rCX

1.7537

(-0.0019)

1.9128

(-0.0006)

2.1428

(0.0000)

θXCF

110.50

(0.03)

110.62

(0.09)

110.92

(0.23)

rCH rCCl

1.0955

(0.0003)

1.0952

(0.0000)

1.0951

(0.0000)

1.7969

(0.0016)

1.7982

(0.0029)

1.7993

(0.0040)

θHCCl

108.22

(-0.03)

108.15

(-0.10)

108.11

(-0.14)

CH3Clc

Intermolecular rX…Cl

3.49

3.47

3.54

sumvdW

3.60

3.75

3.95

θCX…Cl

165.41

169.26

171.57

θCCl…X

87.37

86.23

90.01

a

The values in brackets are the changes induced by the complexation. The values for the van der Waals radii used to calculate sumvdW are 1.80 Å for Cl, 1.95 Å for Br and 2.15 Å for I.41 b

Structural data for the F-atom nearest to the CH3Cl moiety.

c

Structural data for the H-atom nearest to the CF3X moiety.


Page 31 of 38

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Table 3. SAPT decomposition of the interaction energies, in kJ mol-1, for the complexes of CF3X with CH3F and CH3Cl. The MP2/aug-cc-pvdz(-PP) complexation energies, in kJ mol-1, are shown as well for comparison. CH3F

CH3Cl

CF3Cl

CF3Br

CF3I

CF3Cl

CF3Br

CF3I

E(elec.)

-8.1

-12.2

-16.8

-7.0

-10.7

-15.2

E(ind.)

-0.9

-1.9

-3.1

-0.8

-2.7

-6.1

E(disp.)

-5.4

-6.5

-7.3

-7.0

-8.8

-10.1

E(exch.)

6.8

9.3

12.3

8.8

11.4

15.3

∆E (SAPT)

-7.5

-11.2

-14.8

-6.1

-10.8

-16.1

∆E (MP2)

-6.4

-8.7

-10.8

-6.6

-9.1

-11.4



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 4.

Page 32 of 38

Experimental vibrational frequencies and complexation shifts, in cm-1, for the

complexes of CF3Br and CF3I with CH3F dissolved in LKr, at 123 K. The ab initio complexation shifts are derived from the MP2/aug-cc-pVDZ-PP frequencies. Assignment

νmonomer

νcomplex

∆νexp

∆νcalc

CF3Br

ν4 ν4 (13C) ν1 ν2 ν5 ν3 (79Br) ν3 (81Br) ν6

1198.1 1164.2 1075.2 759.4 546.3 352.1 350.3 303.4

1191.5 1157.8 1079.7 758.4 545.8 353.4 351.6

-6.6 -6.4 4.5 -1.0 -0.5 1.3 1.3

-9.2 -9.2 6.5 -2.0 -0.4 1.0 1.0 2.2

CH3F

ν4 ν1

3005.0 2958.8 2855.3 1458.9

3.7 2.2 1.1 -1.0

6.5 3.1

ν5 ν2 ν6 ν3

3001.3 2956.6 2854.2 1459.9 1457.5 1179.2 1035.7

1024.9

-10.8

-14.3

Assignment

νmonomer

νcomplex

∆νexp

∆νcalc

2ν 4 2ν 1 ν2 + ν4 ν1 + ν2 ν4 ν4 (13C) ν1 ν2 ν5 ν3 ν6

2329.9 2126.4 1909.9 1807.1 1175.6 1142.7 1067.4 740.7 539.9 286.4 266.0

2312.1 2135.5 1899.6 1811.5 1166.8 1134.1 1072.9 739.4

-17.8 9.1 -10.3 4.4 -8.8 -8.6 5.5 -1.3

287.2 268.2

0.8 2.2

-19.6 17.0 -11.6 6.7 -9.8 -9.8 8.5 -1.8 -0.4 0.5 1.9

ν4 ν1

3001.3 2956.6 2910.3 2854.2 2055.0 1459.9 1457.5 1179.2 1035.7 1014.7

3008.9 2959.2 2908.7 2855.6 2018.4 1458.4

7.6 2.6 -1.6 1.4 -36.6 -1.5

1017.1 996.7

-18.5 -18.0

CF3I

CH3F

2ν 3 ν5 ν2 ν6 ν3 ν3 (13C)


-1.3 -0.8

9.3 4.7

-39.6 -1.7 -1.1 -1.3 -19.8 -19.8

Page 33 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 5.



complexes of CF3Br and CF3I with CH3Cl dissolved in LKr, at 123 K.

The ab initio

complexation shifts are derived from the MP2/aug-cc-pVDZ-PP frequencies.

CF3Br

CH3Cl

CF3I

CH3Cl

Assignment

νmonomer

νcomplex

∆νexp

∆νcalc

ν2 + ν4 ν4 ν4 (13C) ν1 ν2 ν5 ν3 (79Br) ν3 (81Br) ν6

1951.3 1198.1 1164.2 1075.2 759.4 546.3 352.1 350.3 303.4

1945.8 1193.8 1159.9

-5.5 -4.3 -4.3

758.6 546.1 352.0 350.1

-0.8 -0.2 -0.1 -0.2

-8.5 -6.4 -6.4 2.8 -2.1 -0.5 -1.1 -1.1 1.3

ν4 ν1 ν5 ν2 ν6 ν3 (35Cl) ν3 (37Cl)

3030.6 2958.1 1444.4 1348.6 1016.1 726.1 720.4

2959.1

0.9

1016.6 722.3 716.8

0.5 -3.8 -3.6

2.2 0.5 -2.4 -0.5 0.4 -6.0 -6.0

Assignment

νmonomer

νcomplex

∆νexp

∆νcalc

2ν 4 ν2 + ν4 ν1 + ν2 ν4 ν4 (13C) ν1 ν2 ν5 ν3 ν6

2329.9 1909.9 1807.1 1175.6 1142.7 1067.4 740.7 539.9 286.4 266.0

2315.3 1901.4 1809.1 1168.5 1135.7 1070.8 739.4

-14.4 -8.5 2.0 -7.1 -7.0 3.4 -1.3

285.4

-1.0

-15.0 -9.4 3.3 -7.5 -7.5 5.2 -1.9 -0.5 -1.4 1.0

ν4 ν1 2ν 5 ν5 ν2 ν6 ν3 (35Cl) ν3 (37Cl)

3030.6 2958.1 2864.7 1444.4 1348.6 1016.1 726.1 720.4

3033.9 2958.9 2861.4 1442.2 1348.5

3.3 0.8 -3.3 -2.2 -0.1

718.8 713.3

-7.3 -7.1


3.7 0.9 -5.7 -2.9 -0.6 0.7 -8.4 -8.4


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 6.

Page 34 of 38


complexes of CF3Br and CF3I with C2H5F dissolved in LKr, at 123 K.

The ab initio

complexation shifts are derived from the MP2/aug-cc-pVDZ-PP frequencies. Assignment

νmonomer

νcomplex

∆νexp

∆νcalc

CF3Br

ν2 + ν4 ν1 + ν2 ν4 ν4 (13C) ν1 ν2 ν5 ν3 (79Br) ν3 (81Br) ν6

1951.3 1831.2 1198.1 1164.2 1075.2 759.4 546.3 352.1 350.3 303.4

1942.6 1835.3 1190.4 1156.6 1080.1 758.5 545.8 353.6 351.7 304.5

-8.7 4.1 -7.7 -7.6 4.9 -0.9 -0.5 1.5 1.4 1.8

-11.6 4.8 -9.4 -9.4 7.0 -2.2 -0.4 0.7 0.7 2.2

C2H5F

ν12 ν1 ν13 ν2 ν3 2ν10 ν4 ν5 ν14 ν6 ν7 ν15 ν16 ν8 ν9 ν10 ν17 ν11 ν18

2993.2 2984.9 2960.8 2936.2 2912.7 1750.5 1484.5 1459.2 1443.0 1393.1 1367.6 1290.2 1169.4 1104.7 1045.4 876.5 808.7 414.8 249.7

Assignment 2ν 4 ν2 + ν4 ν1 + ν2 ν4 ν4 (13C) ν1 ν2

CF3I

2966.3

5.5

2915.9 1746.4 1484.0 1459.0 1443.3

3.2 -4.0 -0.5 -0.2 0.3

1367.8

0.2

1105.6 1039.0 873.0

0.9 -6.3 -3.5

251.9

2.2

1.1 0.1 5.3 5.5 -0.1 -11.7 -1.1 -0.4 -0.1 -0.8 0.1 -1.1 -0.9 0.3 -12.7 -5.8 0.1 -0.5 2.3

νmonomer

νcomplex

∆νexp

∆νcalc

2329.9 1909.9 1807.1 1175.6 1142.7 1067.4 740.7

2309.4 1898.2 1811.9 1165.3 1133.1 1073.5 738.7

-20.5 -11.7 4.9 -10.3 -9.5 6.1 -2.0

-21.3 -12.8 8.7 -10.7 -10.7 10.8 -2.1


Page 35 of 38

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C2H5F


ν5 ν3 ν6

539.9 286.4 266.0

ν12 ν1 ν13 ν2 ν3 2ν10 ν4 ν5 ν14 ν6 ν7 ν15 ν16

-0.5 0.2 -2.1

287.0 267.7

0.6 1.7

2993.2 2984.9 2960.8 2936.2 2912.7 1750.5 1484.5 1459.2 1443.0 1393.1 1367.6 1290.2 1169.4

2995.9 2985.8 2969.0

2.7 1.0 8.2

2915.8 1737.4 1483.8 1459.0 1443.3 1392.4 1368.1

3.1 -13.1 -0.7 -0.2 0.3 -0.7 0.5

ν8

1104.7

1102.6

-2.1

0.4

ν9 ν10 ν17 ν11 ν18

1045.4 876.5 808.7 414.8 249.7

1033.9 870.2 809.2

-11.4 -6.3 0.5

-18.4 -8.3 0.2 -1.1 2.6


2.1 0.5 7.6 7.1 0.1 -16.7 -1.3 -0.5 -0.1 -1.0 0.2 -1.5 -1.3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 7.

Page 36 of 38


complexes of CF3Br and CF3I with C2H5Cl dissolved in LKr, at 123 K.

The ab initio

complexation shifts are derived from the MP2/aug-cc-pVDZ-PP frequencies. Assignment

νmonomer

νcomplex

∆νexp

∆νcalc

CF3Br

ν4 ν4 (13C) ν1 ν2 ν5 ν3 (79Br) ν3 (81Br) ν6

1198.1 1164.2 1075.2 759.4 546.3 352.1 350.3 303.4

1192.9 1159.2 1078.0 758.4 545.7 351.9 350.0

-5.2 -5.0 2.8 -1.0 -0.6 -0.2 -0.3

-7.7 -7.7 3.6 -2.5 -0.7 -1.2 -1.2 1.6

C2H5Cl

ν12 ν1 ν13 ν2 ν3 ν4 ν14 ν5 ν6 ν7 ν15 ν8 ν16 ν9 ν17 ν10 (35Cl) ν10 (37Cl) ν11 ν18

3008.5 3001.1 2980.3 2964.2 2884.6 1461.2 1452.9 1441.1 1380.1 1284.7 1247.8 1072.1 1062.3 970.4 784.2 670.4 665.6 335.6 255.9

3010.5

2.0

2982.8 2967.0 2884.0 1461.2 1452.5 1440.5 1380.7

2.5 2.8 -0.6 0.0 -0.4 -0.6 0.6

784.0 665.9 661.0

-0.2 -4.4 -4.6

1.8 0.4 3.0 0.9 0.2 -1.1 -0.2 -1.5 -0.7 -0.5 -0.6 1.5 0.9 -2.3 -1.3 -7.6 -7.6 1.3 1.2

Assignment 2ν 4 ν2 + ν4 ν4 ν4 (13C) ν1 ν2 ν5 ν3 ν6

νmonomer 2329.9 1909.9 1175.6 1142.7 1067.4 740.7 539.9 286.4 266.0

νcomplex 2313.7 1900.5 1167.4 1134.8 1070.5 739.0

∆νexp -16.2 -9.4 -8.2 -7.9 3.1 -1.7

285.2 267.2

-1.2 1.2

CF3I


∆νcalc -15.8 -10.0 -7.9 -7.9 5.0 -2.1 -0.6 -1.7 -0.6

Page 37 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

C2H5Cl


ν12 ν1 ν13 ν2 2ν14 ν3 ν4 ν14 ν5 ν6 ν7 ν15 ν8 ν16 ν9 ν9 (13C) ν17 ν10 (35Cl) ν10 (37Cl) ν11 ν18

3008.5 3001.1 2980.3 2964.2 2935.2 2884.6 1461.2 1452.9 1441.1 1380.1 1284.7 1247.8 1072.1 1062.3 970.4 961.2 784.2 670.4 665.6 335.6 255.9

3009.6

1.1

2980.9 2967.2 2935.6 2882.9 1460.4 1452.0 1437.8 1381.2 1283.9 1247.3 1073.6 1064.3 968.8 959.3 783.9 661.7 657.1

0.6 3.0 0.4 -1.7 -0.8 -0.9 -3.3 1.1 -0.8 -0.5 1.5 2.0 -1.6 -1.9 -0.3 -8.6 -8.5


1.2 0.7 1.2 0.5 -0.9 0.5 -1.4 -0.5 -1.6 0.9 -0.7 -1.2 0.8 1.6 -2.7 -2.7 -0.9 -9.0 -9.0 -0.5 3.4


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 38

For Table of Contents Only Infrared and Raman study of the complexes of the trifluoromethanes CF3X (X = Cl, Br or I) with fluorineand chlorine-electron donors dissolved in liquid krypton.


Double-inversion mechanisms of the X⁻ + CH₃Y [X,Y = F, Cl, Br, I] SN2 reactions.

Structural, Electronic, and Optical Properties of BiOX1-xYx (X, Y = F, Cl, Br, and I) Solid Solutions from DFT Calculations.

The nature of inter- and intramolecular interactions in F2OXe(…)HX (X= F, Cl, Br, I) complexes.

Insertion of alkynes into Pt-X bonds of square planar [PtX2(N^N)] (X = Cl, Br, I) complexes.

Surprising quenching of the spin-orbit interaction significantly diminishes H2O···X [X = F, Cl, Br, I] dissociation energies.

Communication: covalent nature of X⋯H2O (X = F, Cl, and Br) interactions.

The X-C···π (X = F, Cl, Br, CN) carbon bond.

The electronic mechanism ruling the dihydrogen bonds and halogen bonds in weakly bound systems of H3SiH···HOX and H 3SiH···XOH (X = F, Cl, and Br).

Parity violation in nuclear magnetic resonance frequencies of chiral tetrahedral tungsten complexes NWXYZ (X, Y, Z = H, F, Cl, Br or I).

Why Is the L-Shaped Structure of X2···X2 (X = F, Cl, Br, I) Complexes More Stable Than Other Structures?

The competition of Y⋯O and X⋯N halogen bonds to enhance the group V σ-hole interaction in the NCY⋯O=PH3 ⋯NCX and O=PH3 ⋯NCX⋯NCY (X, Y=F, Cl, and Br) complexes.

Novel germanetellones: XYGe=Te (X, Y = H, F, Cl, Br, I and CN) - structures and energetics. Comparison with the first synthetic successes.

Theoretical study of X⁻ · 1 · YF (1 = triazine, X = Cl, Br and I, Y = H, Cl, Br, I, PH₂ and AsH₂): noncovalently electron-withdrawing effects on anion-arene interactions.

Protic anions [H(B12X12)]- (X = F, Cl, Br, I) that act as Brønsted acids in the gas phase.

Comparison of halogen bonds in M-X⋯N contacts (M = C, Si, Ge and X = Cl, Br).

The competition of σ-hole···Cl(-) and π-hole···Cl(-) bonds between C6F5X (X = F, Cl, Br, I) and the chloride anion and its potential application in separation science.

Polymorphism in 2-X-adamantane derivatives (X = Cl, Br).

Matrix-isolation and computational study of the HXeY⋯H2O complexes (Y = Cl, Br, and I).

Computational study on thermochemical properties for perhalogenated methanols (CX3OH) (X = F, Cl, Br).

Gold Bonding in Small Molecule⋅⋅⋅M-X (X=F, Cl, Br, CH3, CF3) Complexes.

Synthesis, structure and photophysical properties of [UO2X2(O=PPh3)2] (X = Cl, Br, I).

Structural and electronic properties of silicene on MgX₂ (X = Cl, Br, and I).

Manifestation of long-range ordered state in layered VX2 (X = Cl, Br, I) systems.

Engineering BiOX (X = Cl, Br, I) nanostructures for highly efficient photocatalytic applications.