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Exploring “aerogen–hydride” interactions between ZOF2 (Z = Kr, Xe) and metal hydrides: An ab initio study
Accepted Manuscript Exploring “aerogen-hydride” interactions between ZOF2 (Z= Kr, Xe) and metal hydrides: An ab initio study Mehdi D. Esrafili, Fariba Mohammadian-Sabet PII: DOI: Reference:
S0009-2614(16)30289-5 http://dx.doi.org/10.1016/j.cplett.2016.05.010 CPLETT 33848
To appear in:
Chemical Physics Letters
Received Date: Accepted Date:
4 March 2016 3 May 2016
Please cite this article as: M.D. Esrafili, F. Mohammadian-Sabet, Exploring “aerogen-hydride” interactions between ZOF2 (Z= Kr, Xe) and metal hydrides: An ab initio study, Chemical Physics Letters (2016), doi: http://dx.doi.org/ 10.1016/j.cplett.2016.05.010
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Exploring “aerogen-hydride” interactions between ZOF2 (Z= Kr, Xe) and metal hydrides: An ab initio study Mehdi D. Esrafili* and Fariba Mohammadian-Sabet Laboratory of Theoretical Chemistry, Department of Chemistry, University of Maragheh, Maragheh, Iran * Corresponding Author. Phone: (+98) 4212237955. Fax: (+98) 4212276060. P.O. Box: 5513864596. E-mail: [email protected].
Abstract In this work, a new σ-hole interaction formed between ZOF2 (Z = Kr and Xe) as the Lewis acid and a series of metal-hydrides HMX (M = Be, Mg, Zn and X= H, F, CN, CH3) is reported. The nature of this interaction, called “aerogen-hydride” interaction, is unveiled by molecular electrostatic potential, non-covalent interaction, quantum theory of atoms in molecules and natural bond orbital analyses. Our results indicate that the aerogen-hydride interactions are quite strong and can be comparable in strength to other σ-hole bonds. An important chargetransfer interaction is also associated with the formation of OF2Z···HMX complexes. Key words: Noncovalent interaction; MEP; σ-hole; QTAIM; NBO.
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1. Introduction In 2007, the concept ‘‘σ-hole’’ was firstly introduced by Politzer and co-workers [1] to explain the attractive interaction between the covalently-bonded halogen atoms and Lewis bases. This concept was then expanded by these authors to some covalently-bonded Group 14-16 atoms [2-10]. The term σ-hole refers to an electron-deficient region developed on the outermost portion of an atomic surface, as a result of its nonuniform electron density distribution upon the covalent bonding with an electron-withdrawing group. If this region has enough positive electrostatic potential, it can interact attractively with negative sites on the same or more often other molecules, giving rise to a stable and highly directional noncovalent interaction. Such strong interactions are often referred to the halogen-bonding [11-13], chalcogen-bonding [14-17], pnicogen-bonding [18-23] and tetrel-bonding [24-27] for the atoms of Groups 17, 16, 15 and 14, respectively. All these σ-hole interactions share almost the same features and are ruled by the same mechanism. Although the possibility of Group 18 atoms (known as rare gases or aerogens) to act as a Lewis acid center has been reported for several years [28,29], however, recent studies [30-35] demonstrated a theoretical evidence for the favorable noncovalent interaction between some rare gas containing molecules and potential electron donors. The resulting “aerogen bonds” were found to be fairly strong and can be comparable in strength to hydrogen bonds and other σ-hole interactions [30]. Like other σ-hole interactions, a detailed molecular electrostatic potential (MEP) analysis indicates that the electrostatic interaction between the positive σ-hole on the aerogen atom, located approximately on the extension of the covalent bonds to this atom, and the negative site on the Lewis base is the main source of the formation and directionality of aerogenbonds. On the other hand, the stability of aerogen-bonded complexes can be partly due to the transfer of electronic density from the bonding orbital in the Lewis base to the antibonding orbital of the Lewis acid. It is well-known that the negatively charged hydride atom in metal hydrides can act as a potential electron donor to form σ-hole interactions with Group 14-17 atoms [36-39]. Therefore, the characterization of such a novel type σ-hole interaction between aerogen atoms and metal hydrides should be an interesting research topic. The aim of the present work is to study aerogen bond interactions between ZOF2 (Z=Kr, Xe) and HMX metal-hydrides (M=Be, Mg, Zn; X=H, F, 2
CN and CH3) with quantum chemical calculations. A particular attention is paid into the nature of aerogen-hydride interactions by means of MEP, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. We think that the results of this study can be enrich our knowledge on rare gases chemistry and also important for the extension of σ-hole interactions in supramolecular chemistry. 2. Computational details All ab initio calculations were carried out within the Gaussian 09 electronic structure package [40]. The second-order Moller-Plesset perturbation theory (MP2) was used to optimize the monomers and binary complexes. The Xe atom was described with the aug-cc-pVTZ-PP basis set [41], which uses a relativistic effective core potential to account for relativistic effects in this atom. For the remaining atoms, the standard aug-cc-pVTZ basis set was employed. In order to confirm whether the optimized geometries correspond to energy minima on potential energy surface, subsequent harmonic frequency calculations were performed at the same level. The interaction energies were calculated as the difference between the total energy of the complexes minus the sum of the energies of the isolated monomers. The basis set superposition error was estimated using the counterpoise (CP) method [42]. The MEP isosurfaces (0.001 electrons Bohr-3) of the isolated KrOF2 and XeOF2 were calculated at the MP2/aug-cc-pVTZ(-PP) level with the wave function analysis–surface analysis suite (WFA-SAS) [43]. The noncovalent interaction (NCI) analysis [44] was performed with the Multiwfn program [45]. The QTAIM [46] analysis was performed using the AIM2000 program [47], with the MP2/aug-cc-pVTZ(-PP) wave functions. The NBO analysis [48] was carried out at the HF/aug-cc-pVTZ level using the NBO module within the Gaussian 09. The
83
Kr and
131
Xe
chemical shielding isotropies as well as spin-spin coupling constants across the aerogen-hydride bonds were calculated with the gauge-included atomic orbital (GIAO) approach [49]. 3. Results and discussion The optimized structures of OF2Z···HMX (Z = Kr, Xe; M = Be, Mg, Zn; X= H, F, CN, CH3) complexes are shown in Figure S1 of Supporting Information. No symmetry constraint was introduced in the optimization of these complexes. The frequency calculations reveal that all these species are true minima on the potential energy surface, since there is no imaginary frequency. Table 1 lists the binding distances in the OF2Z···HMX complexes. In these 3
complexes, the hydrogen atom of HMX molecule points toward the Z atom of ZOF2 with the ZO bond in an opposite direction. The negatively charged H atom of HMX moiety could shift the electron density toward the σ-hole on the Z atom in ZOF2, as depicted in the electrostatic potential map of ZOF2 in Figure 1. We name this interaction as the ‘‘aerogen-hydride’’ in view of the concepts of aerogen and dihydrogen bonds. The Z···H binding distances in the KrOF2 and XeOF2 complexes are in the range of 2.375-2.623 and 2.362-2.628 Å, respectively (Table 1). All these binding distances are smaller than the sum of van der Waals (vdW) radii of the respective atoms [50], which implies that there is an attractive interaction between the ZOF2 and HMX molecules. Besides, these aerogen-hydride distances are much smaller than those of aerogennitrogen [30] or aerogen-π [35] interactions. One can see that the presence of the electronwithdrawing groups (F and CN) in the HMX molecule causes an increase of the binding distance, while the electron-donating group (CH3) leads to a shortening of the binding distance. For a given X, the KrOF2 also tends to form relatively shorter Z···H binding distances than XeOF2 counterparts, which should be due to the smaller vdW radius of Kr (2.02 Å) compared to that of Xe atom (2.16 Å) [50]. Accompanied with the complex formation, the H-M bond distance of the HMX is elongated by 0.0009-0.0121 Å (Table 1). These values are compatible with those of the corresponding H-M bond elongation in pnicogen- [36], chalcogen- [37] or tetrel-hydride [27,51] interactions. The elongation of the H-M bond is larger in the Xe complexes than that in the Kr counterparts, indicative the strong aerogen-hydride interaction in the former complexes. Also, the H-M bond elongation is more important in the Mg complexes compared to those of Be and Zn, which may be attributed to the greater strength of the Z···H interactions in these complexes. As evident from Table 1, the predicted harmonic frequencies of the H-M stretching modes are in the range of 1665–2292 cm-1, which are larger than those of the tetrel-hydride interactions in XH3Si···HMX complexes [27]. This can be related to the strong Z···H interaction in the title complexes. The results of Table 1 also indicate that upon the complex formation, a blue shift is occurred for the H-M stretch vibrations. The calculated ∆νM-H values are between 7 (in F2OKr···HZnCN) and 67 cm-1 (in F2OXe···HMgCH3). It is noteworthy that such a blue shift of the νM-H is not consistent with the elongation of the H–M bond due to complexation. However, this conflicting phenomenon was also reported in other σ-hole interactions like halogen-hydride 4
[52] and chalcogen-hydride [37], most likely due to a complex combination of electrostatic, charge-transfer and polarization effects between the interacting molecules. For a given Z= Kr or Xe, the amount of shift in the H-M frequency depends on the nature of the electron donating/withdrawing of the X substituent and becomes larger in the order X= CH3 > F > H > CN. The existence of aerogen-hydride bond in the F2OZ···HMX complexes can be verified by the NCI index analysis. Figure S2 of Supporting Information exhibits a plot of the reduced density gradient (RDG) versus sign (λ2)ρ of these complexes. As evident, a low-gradient spike in the low-energy, low-density region (about -0.030 au) is present, which should be correspond to the aerogen-hydride interaction in these systems. Note that in some Kr complexes, there is also an additional spike located at low-density regions, which is due to the weak electrostatic interaction between the F and M atoms in these systems. One can also see that as the strength of the Z···H interaction increases, the location of the spike has a greater deviation from zero and the shape of the spike becomes broader. This indicates that NCI analysis can be considered as a powerful method for predicting the aerogen-hydride interactions. Table 1 collects the calculated interaction energies of the OF2 Z···HMX complexes at the MP2/aug-cc-pVTZ(-PP) level. To obtain more accurate and reliable interaction energies, a single point energy was also calculated at the CCSD(T)/aug-cc-pVTZ(-PP) level. From Table 1, it is evident that the interaction energies in the Xe complexes are more negative than those of the Kr counterparts, which is consistent with the calculated electrostatic potential maximum on these atoms (Figure 1). In addition, when the electron donor varies from HBeX through HZnX to HMgX, the interaction energy of Z···H becomes more negative. The estimated MP2 interaction energies of these complexes are between -2.18 and -9.72 kcal/mol, which are smaller (less negative) than those of OF2Z···NH3 and OF2 Z···NCCH3 [30] complexes. It is also apparent that the MP2 and CCSD(T) interaction energies are consistent with each other. The largest difference in the interaction energies at both levels is about 0.4 kcal/mol which shows a deviation of less than 8% from the CCSD(T) results. This suggests that the MP2 method can be regarded as a reliable method for description of aerogen-hydride interactions. Besides, the calculated BSSE values of these complexes account for about 15-24 and 14-22 % of the uncorrected MP2 and
5
CCSD(T) interaction energies, respectively, which clearly shows that the CP correction has a small effect on the interaction energies of the aerogen-hydride bonds studied here. Results from a series of extensive studies [53-55] have recommended the use of bond functions placed between interacting monomers as an effective approach to obtain accurate intermolecular potentials of weakly bound systems. Tao and coworkers [56-61] found that an extended but only roughly optimized 3s3p2d set located in the middle of the van der Waals bond can be used in many different complexes and provide reliable results for interaction energies of complexes involving rare gas atoms. By augmenting the aug-cc-pVTZ(-PP) basis set with a set of appropriate bond functions, similar to that of Tao and coworkers [61], interaction energies of OF2Z···HMH complexes were calculated at the both MP2 and CCSD(T) levels (Table S1). Examination of these results leads to the conclusion that the use of midbond functions has a pronounce effect on the interaction energies of these systems, which is consistent with primary expectation for the role of midbond functions. Besides, these effects seem to be more important for the Xe complexes, may be due to the larger dispersion effects in these systems. Table 1 also summarizes the calculated change in Enthalpy (ΔH298) and Gibbs free energy (ΔG298) associated with the formation of the OF2Z···HMX complexes at the MP2/aug-ccpVTZ(-PP) level. It is seen that for the all complexes considered, the ΔH298 values are negative, which demonstrates that the formation of these complexes is exothermic under ambient condition. However, the positive ΔG298 values indicate that these gas phase complexes would be thermodynamically unstable at 298 K and therefore the equilibrium concentrations of these complexes will be small at this temperature. Nonetheless, the results of Table 1 indicate that the OF2Z···HMX complexes ought to be experimentally observable in the gas phase, mainly at low temperature. To understand the nature of the aerogen-hydride interactions in the title complexes, the QTAIM analysis was performed. Table 2 summarizes the electron density (ρBCP), its Laplacian (∇2ρBCP) and electron energy density (HBCP) values at the Z···H bond critical points (BCPs). It is evident that the ρBCP values at Kr···H BCPs are in the range of 0.015-0.036 au, while those of Xe···H are between 0.016 and 0.040 au. All these values are consistent with the criteria proposed by Koch and Popelier for noncovalent interactions [62]. In addition, the electron density at BCP can be usually regarded as an indicator of the strength of noncovalent interactions [63-65]. As 6
Figure 2 indicates, the calculated ρBCP values correlate exponentially with Z···H binding distances, with a squared correlation coefficient of about 0.99. The corresponding ∇2ρBCP values are always positive and are between 0.044 and 0.096 au. As Table 2 indicates, all strong Z···H interactions have a negative value of the energy density (HBCP) at the BCPs, indicating that these interactions are partly covalent in nature. Table 2 lists the calculated second-order charge-transfer energies (E(2)) and the corresponding charge-transfer values due to the formation of OF2Z···HMX complexes. It is seen that for all of the binary F2OZ:HMX complexes, the main interaction responsible for the stabilization of the complexes arises from the second-order orbital interaction of the donor σM-H * orbital of the HMX with the Z O acceptor orbital of ZOF2. The charge-transfer energies due to
this interaction are in the range of 1.31-7.64 and 1.30-8.31 kcal/mol for Kr and Xe complexes, respectively. For a given Z, the calculated E(2) values in the F2OZ···HMX complexes decrease in the order X= CH3 > H > F > CN and M= Mg > Zn ≈ Be. Moreover, accompanied with this orbital interaction, a charge of about 0.003-0.044 e is transferred from the σM-H orbital of the * Lewis base to the Z O orbital of ZOF2 molecule.
The 83Kr or 131Xe absolute chemical shieldings (σ) in the binary complexes and changes in these quantities with respect to the isolated ZOF2 molecule are reported in Table 3. The calculated σ values are in the range of 270.85-285.80 and 88.68-93.29 ppm for the Kr and Xe complexes, respectively. For both series, the formation of complex leads to a significant decrease in σ value. As expected, the Xe complexes exhibit a larger change in σ value than their Kr counterparts. Also, the nature of the substituent X in the binary complexes can influence the amount of the change in σ values. Table 3 also lists the calculated 1pJ(Z–H) spin-spin constants of the OF2 Z···HMX complexes. One can see that the
1p
J(Z–H) values range from -0.13 Hz in
F2OKr···HBeF to -0.55 Hz in F2OXe···HMgCH3 , which indicates the sensitivity of
1p
J(Z–H)
coupling constants to the nature of substituents. However, there is no correlation between the 1p
J(Z–H) values and the interaction energies, or the binding distances and change in the absolute
chemical shieldings in the binary complexes relative to the corresponding monomers. It is expected that the formation of the F2OZ···HMX complexes induces an internal electronic rearrangement within each monomer. Figure 3 indicates the electron density shifts in the F2OZ···HMgX complexes, where red and green regions show loss and gain of electron 7
density, respectively. It is evident that all these complexes exhibit almost a similar pattern, that is, a significant electron density accumulation is occurred on the H atom, while a loss in the H-M bond region. The degree of this electron density accumulation or depletion increases in the order of X= CN < F < H < CH3, which is consistent with the calculated interaction energies of these complexes (Table 1). There is also a significant loss of electron density on the σ-hole region of the Z atom, which is due to the polarization of this atom by the electric field of the negatively charged H atom of HMgX molecule. 4. Conclusion In this work, ab initio calculations were performed to investigate the possible σ-hole interactions in the binary OF2Z···HMX complexes, where (Z= Kr, Xe; M = Be, Mg, Zn and X= H, F, CN, CH3). This new type of interaction was named as the aerogen-hydride, since it involves the covalently-bonded Group 18 atoms (aerogens) as the Lewis acid. The calculated Z···H binding distances were found to be in the range of 2.375-2.623 and 2.362-2.628 Å for the KrOF2 and XeOF2 complexes, respectively. Upon the complex formation, a blue shift was found for the H–M stretch vibrations. Our results also indicated that all these gas phase complexes would be thermodynamically unstable at 298 K. However, the negative ∆H (and ΔS) values suggest that a decrease in temperature will lead to an increase in the equilibrium concentration of these species. All of the strong aerogen-hydride interactions were characterized with a negative HBCP value, indicating that these interactions are partly covalent in nature. Moreover, the stability of these aerogen-hydride complexes can be attributed partly to the transfer of electronic density * from the σM-H in the HMX to the Z O in the XeOF2 or KrOF2. Finally, the formation of
OF2Z···HMX complexes leads to a decrease in 83Kr or 131Xe absolute chemical shielding values.
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Figure 1. Molecular electrostatic potential map of the isolated KrOF 2 and XeOF2 molecules. Color range, in kcal/mol, is: red > 40.9; 20.0 < yellow < 40.9; 0 < green < 20.0; blue < 0. The black and blue circles indicate the surface maxima and minima, respectively. The electrostatic potential value of σ-hole
associated with the Kr-O or Xe-O bond is given in kcal/mol.
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Figure 2. Correlation between the binding distances and electron densities at Z···H BCPs
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Figure 3. Electron density difference (±0.001 au) of F2OZ:HMgX. Red and green regions
indicate regions of decreased and increased electron densities, respectively.
13
Table 1. Binding distance (Rint, Å), change of H-M bond length (∆R, Å), stretching frequency (ν, cm-1), shift of stretching frequencies (∆ν, cm-1), interaction energy (Eint, kcal/mol), change of MP 2 CCSD( T ) complex Rint ∆RH-M νM-H ∆νM-H Eint ∆H298 ∆G298 T Eint F2OKr···HBeCN 2.615 0.0015 2260 9 -2.18 -2.09 -4.07 2.40 188 F2OKr···HBeF 2.602 0.0012 2250 10 -3.01 -2.88 -5.14 0.65 265 F2OKr···HBeH 2.558 0.0026 2292 17 -4.14 -4.01 -5.52 0.24 286 F2OKr···HBeCH3 2.510 0.0038 2185 20 -4.68 -4.48 -6.68 1.76 236 F2OKr···HMgCN 2.453 0.0021 1752 23 -6.09 -5.90 -7.27 1.11 259 F2OKr···HMgF 2.439 0.0021 1741 25 -7.03 -6.88 -8.10 1.67 247 F2OKr···HMgH 2.376 0.0081 1691 38 -8.24 -8.12 -10.05 0.59 282 F2OKr···HMgCH3 2.375 0.0096 1673 41 -9.27 -9.03 -3.03 5.35 108 F2OKr···HZnCN 2.600 0.0011 2122 7 -2.20 -2.08 -3.01 5.21 109 F2OKr···HZnF 2.623 0.0009 2141 8 -2.19 -2.10 -5.56 0.65 267 F2OKr···HZnH 2.508 0.0051 2032 14 -5.01 -4.62 -7.36 3.54 201 F2OKr···HZnCH3 2.476 0.0053 2017 16 -5.61 -5.35 -3.16 3.18 149 F2OXe···HBeCN 2.628 0.0030 2241 15 -2.41 -2.33 -4.18 2.13 198 F2OXe···HBeF 2.606 0.0028 2234 18 -3.14 -2.92 -5.21 0.50 272 F2OXe···HBeH 2.567 0.0048 2287 22 -4.26 -3.95 -5.85 0.14 291 F2OXe···HBeCH3 2.536 0.0052 2166 26 -4.97 -4.60 -7.75 1.63 246 F2OXe···HMgCN 2.460 0.0071 1733 34 -6.26 -6.17 -8.45 0.83 271 F2OXe···HMgF 2.443 0.0068 1724 37 -6.97 -6.74 -10.32 1.10 269 F2OXe···HMgH 2.386 0.0121 1678 59 -8.98 -8.66 -11.43 0.30 291 F2OXe···HMgCH3 2.362 0.0121 1665 67 -9.72 -8.92 -3.22 2.67 163 F2OXe···HZnCN 2.613 0.0032 2102 13 -2.33 -2.21 -3.12 3.24 146 F2OXe···HZnF 2.626 0.0037 2125 15 -2.30 -2.18 -6.07 0.10 293 F2OXe···HZnH 2.512 0.0086 2017 24 -5.14 -4.96 -7.79 3.09 213 F2OXe···HZnCH3 2.481 0.0089 2002 30 -5.88 -5.65 -3.35 2.55 169 Enthalpy (∆H298, kcal/mol) and free energy (∆G298, kcal/mol), and a value of temperature (T, K), where ∆G is negative of F2OZ···HMX complexes
14
Table 2. Topological parameters of electron density (electron density at BCP, ρBCP, its * Laplacian, ∇2ρBCP, and total electron energy density, HBCP) and calculated σM-H → Z O chargetransfer energy (E(2)) and the associated charge-transfer (qCT) of F2OZ···HMX a complex ρBCP HBCP E(2) ∇2ρBCP F2OKr···HBeCN 0.015 0.045 0.001 1.31 F2OKr···HBeF 0.016 0.047 0.001 1.49 F2OKr···HBeH 0.018 0.050 0.000 2.11 F2OKr···HBeCH3 0.021 0.052 0.000 2.50 F2OKr···HMgCN 0.025 0.056 -0.001 4.34 F2OKr···HMgF 0.027 0.057 -0.001 4.83 F2OKr···HMgH 0.034 0.062 -0.002 6.78 F2OKr···HMgCH3 0.036 0.063 -0.003 7.64 F2OKr···HZnCN 0.016 0.045 0.000 1.30 F2OKr···HZnF 0.015 0.044 0.000 1.39 F2OKr···HZnH 0.021 0.053 0.000 2.85 F2OKr···HZnCH3 0.025 0.056 -0.001 3.31 F2OXe···HBeCN 0.016 0.057 0.001 1.45 F2OXe···HBeF 0.017 0.060 0.001 1.88 F2OXe···HBeH 0.019 0.066 0.000 2.25 F2OXe···HBeCH3 0.021 0.070 0.000 2.74 F2OXe···HMgCN 0.027 0.079 -0.002 4.78 F2OXe···HMgF 0.029 0.082 -0.003 5.17 F2OXe···HMgH 0.036 0.092 -0.006 7.33 F2OXe···HMgCH3 0.040 0.096 -0.009 8.31 F2OXe···HZnCN 0.017 0.058 0.001 1.75 F2OXe···HZnF 0.017 0.055 0.001 1.80 F2OXe···HZnH 0.023 0.071 -0.001 3.20 F2OXe···HZnCH3 0.026 0.076 -0.001 3.94 a
All ρBCP, ∇2ρBCP and HBCP values in au, E(2) in kcal/mol and qCT in e.
qCT 0.003 0.004 0.005 0.006 0.010 0.011 0.016 0.019 0.003 0.004 0.007 0.008 0.004 0.005 0.007 0.008 0.017 0.018 0.032 0.044 0.005 0.004 0.009 0.012
15
Table 3. 83Kr or 131Xe absolute chemical shielding (σ, ppm), corresponding change with respect to the isolated monomer (Δσ, ppm) and Z-H spin-spin constant (1PJ(Z–H), Hz) of F2OZ···HMX complexes complex F2OKr···HBeCN F2OKr···HBeF F2OKr···HBeH F2OKr···HBeCH3 F2OKr···HMgCN F2OKr···HMgF F2OKr···HMgH F2OKr···HMgCH3 F2OKr···HZnCN F2OKr···HZnF F2OKr···HZnH F2OKr···HZnCH3 F2OXe···HBeCN F2OXe···HBeF F2OXe···HBeH F2OXe···HBeCH3 F2OXe···HMgCN F2OXe···HMgF F2OXe···HMgH F2OXe···HMgCH3 F2OXe···HZnCN F2OXe···HZnF F2OXe···HZnH F2OXe···HZnCH3
σ 284.23 285.80 282.09 276.99 285.62 279.08 275.52 275.80 282.79 279.78 273.57 270.85 93.28 93.29 92.79 90.93 91.32 90.48 89.53 89.61 91.73 91.51 89.85 88.68
Δσ -2.11 -2.10 -2.67 -3.48 -4.25 -4.89 -5.58 -6.02 -2.58 -2.72 -2.90 -3.89 -3.32 -3.30 -3.80 -5.67 -5.28 -6.11 -6.99 -7.06 -4.87 -5.08 -6.74 -7.91
1P
J(Z–H) -0.14 -0.13 -0.22 -0.24 -0.20 -0.26 -0.38 -0.44 -0.16 -0.16 -0.24 -0.27 -0.17 -0.15 -0.29 -0.28 -0.24 -0.35 -0.50 -0.55 -0.24 -0.18 -0.43 -0.49
16
Graphical abstract
Research highlights: 1- A σ-hole interaction between Group 18 atoms and a series of metal-hydrides molecules is reported for the first time. 2- Upon the complex formation, a blue shift is occurred for the H-M stretch vibrations. 3- An important charge-transfer interaction is associated with the formation of these complexes. 4- The formation of OF2 Z···HMX complexes leads to a decrease in chemical shielding values.
83
Kr or
131
Xe absolute
17
S0009-2614(16)30289-5 http://dx.doi.org/10.1016/j.cplett.2016.05.010 CPLETT 33848
To appear in:
Chemical Physics Letters
Received Date: Accepted Date:
4 March 2016 3 May 2016
Please cite this article as: M.D. Esrafili, F. Mohammadian-Sabet, Exploring “aerogen-hydride” interactions between ZOF2 (Z= Kr, Xe) and metal hydrides: An ab initio study, Chemical Physics Letters (2016), doi: http://dx.doi.org/ 10.1016/j.cplett.2016.05.010
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Exploring “aerogen-hydride” interactions between ZOF2 (Z= Kr, Xe) and metal hydrides: An ab initio study Mehdi D. Esrafili* and Fariba Mohammadian-Sabet Laboratory of Theoretical Chemistry, Department of Chemistry, University of Maragheh, Maragheh, Iran * Corresponding Author. Phone: (+98) 4212237955. Fax: (+98) 4212276060. P.O. Box: 5513864596. E-mail: [email protected].
Abstract In this work, a new σ-hole interaction formed between ZOF2 (Z = Kr and Xe) as the Lewis acid and a series of metal-hydrides HMX (M = Be, Mg, Zn and X= H, F, CN, CH3) is reported. The nature of this interaction, called “aerogen-hydride” interaction, is unveiled by molecular electrostatic potential, non-covalent interaction, quantum theory of atoms in molecules and natural bond orbital analyses. Our results indicate that the aerogen-hydride interactions are quite strong and can be comparable in strength to other σ-hole bonds. An important chargetransfer interaction is also associated with the formation of OF2Z···HMX complexes. Key words: Noncovalent interaction; MEP; σ-hole; QTAIM; NBO.
1
1. Introduction In 2007, the concept ‘‘σ-hole’’ was firstly introduced by Politzer and co-workers [1] to explain the attractive interaction between the covalently-bonded halogen atoms and Lewis bases. This concept was then expanded by these authors to some covalently-bonded Group 14-16 atoms [2-10]. The term σ-hole refers to an electron-deficient region developed on the outermost portion of an atomic surface, as a result of its nonuniform electron density distribution upon the covalent bonding with an electron-withdrawing group. If this region has enough positive electrostatic potential, it can interact attractively with negative sites on the same or more often other molecules, giving rise to a stable and highly directional noncovalent interaction. Such strong interactions are often referred to the halogen-bonding [11-13], chalcogen-bonding [14-17], pnicogen-bonding [18-23] and tetrel-bonding [24-27] for the atoms of Groups 17, 16, 15 and 14, respectively. All these σ-hole interactions share almost the same features and are ruled by the same mechanism. Although the possibility of Group 18 atoms (known as rare gases or aerogens) to act as a Lewis acid center has been reported for several years [28,29], however, recent studies [30-35] demonstrated a theoretical evidence for the favorable noncovalent interaction between some rare gas containing molecules and potential electron donors. The resulting “aerogen bonds” were found to be fairly strong and can be comparable in strength to hydrogen bonds and other σ-hole interactions [30]. Like other σ-hole interactions, a detailed molecular electrostatic potential (MEP) analysis indicates that the electrostatic interaction between the positive σ-hole on the aerogen atom, located approximately on the extension of the covalent bonds to this atom, and the negative site on the Lewis base is the main source of the formation and directionality of aerogenbonds. On the other hand, the stability of aerogen-bonded complexes can be partly due to the transfer of electronic density from the bonding orbital in the Lewis base to the antibonding orbital of the Lewis acid. It is well-known that the negatively charged hydride atom in metal hydrides can act as a potential electron donor to form σ-hole interactions with Group 14-17 atoms [36-39]. Therefore, the characterization of such a novel type σ-hole interaction between aerogen atoms and metal hydrides should be an interesting research topic. The aim of the present work is to study aerogen bond interactions between ZOF2 (Z=Kr, Xe) and HMX metal-hydrides (M=Be, Mg, Zn; X=H, F, 2
CN and CH3) with quantum chemical calculations. A particular attention is paid into the nature of aerogen-hydride interactions by means of MEP, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. We think that the results of this study can be enrich our knowledge on rare gases chemistry and also important for the extension of σ-hole interactions in supramolecular chemistry. 2. Computational details All ab initio calculations were carried out within the Gaussian 09 electronic structure package [40]. The second-order Moller-Plesset perturbation theory (MP2) was used to optimize the monomers and binary complexes. The Xe atom was described with the aug-cc-pVTZ-PP basis set [41], which uses a relativistic effective core potential to account for relativistic effects in this atom. For the remaining atoms, the standard aug-cc-pVTZ basis set was employed. In order to confirm whether the optimized geometries correspond to energy minima on potential energy surface, subsequent harmonic frequency calculations were performed at the same level. The interaction energies were calculated as the difference between the total energy of the complexes minus the sum of the energies of the isolated monomers. The basis set superposition error was estimated using the counterpoise (CP) method [42]. The MEP isosurfaces (0.001 electrons Bohr-3) of the isolated KrOF2 and XeOF2 were calculated at the MP2/aug-cc-pVTZ(-PP) level with the wave function analysis–surface analysis suite (WFA-SAS) [43]. The noncovalent interaction (NCI) analysis [44] was performed with the Multiwfn program [45]. The QTAIM [46] analysis was performed using the AIM2000 program [47], with the MP2/aug-cc-pVTZ(-PP) wave functions. The NBO analysis [48] was carried out at the HF/aug-cc-pVTZ level using the NBO module within the Gaussian 09. The
83
Kr and
131
Xe
chemical shielding isotropies as well as spin-spin coupling constants across the aerogen-hydride bonds were calculated with the gauge-included atomic orbital (GIAO) approach [49]. 3. Results and discussion The optimized structures of OF2Z···HMX (Z = Kr, Xe; M = Be, Mg, Zn; X= H, F, CN, CH3) complexes are shown in Figure S1 of Supporting Information. No symmetry constraint was introduced in the optimization of these complexes. The frequency calculations reveal that all these species are true minima on the potential energy surface, since there is no imaginary frequency. Table 1 lists the binding distances in the OF2Z···HMX complexes. In these 3
complexes, the hydrogen atom of HMX molecule points toward the Z atom of ZOF2 with the ZO bond in an opposite direction. The negatively charged H atom of HMX moiety could shift the electron density toward the σ-hole on the Z atom in ZOF2, as depicted in the electrostatic potential map of ZOF2 in Figure 1. We name this interaction as the ‘‘aerogen-hydride’’ in view of the concepts of aerogen and dihydrogen bonds. The Z···H binding distances in the KrOF2 and XeOF2 complexes are in the range of 2.375-2.623 and 2.362-2.628 Å, respectively (Table 1). All these binding distances are smaller than the sum of van der Waals (vdW) radii of the respective atoms [50], which implies that there is an attractive interaction between the ZOF2 and HMX molecules. Besides, these aerogen-hydride distances are much smaller than those of aerogennitrogen [30] or aerogen-π [35] interactions. One can see that the presence of the electronwithdrawing groups (F and CN) in the HMX molecule causes an increase of the binding distance, while the electron-donating group (CH3) leads to a shortening of the binding distance. For a given X, the KrOF2 also tends to form relatively shorter Z···H binding distances than XeOF2 counterparts, which should be due to the smaller vdW radius of Kr (2.02 Å) compared to that of Xe atom (2.16 Å) [50]. Accompanied with the complex formation, the H-M bond distance of the HMX is elongated by 0.0009-0.0121 Å (Table 1). These values are compatible with those of the corresponding H-M bond elongation in pnicogen- [36], chalcogen- [37] or tetrel-hydride [27,51] interactions. The elongation of the H-M bond is larger in the Xe complexes than that in the Kr counterparts, indicative the strong aerogen-hydride interaction in the former complexes. Also, the H-M bond elongation is more important in the Mg complexes compared to those of Be and Zn, which may be attributed to the greater strength of the Z···H interactions in these complexes. As evident from Table 1, the predicted harmonic frequencies of the H-M stretching modes are in the range of 1665–2292 cm-1, which are larger than those of the tetrel-hydride interactions in XH3Si···HMX complexes [27]. This can be related to the strong Z···H interaction in the title complexes. The results of Table 1 also indicate that upon the complex formation, a blue shift is occurred for the H-M stretch vibrations. The calculated ∆νM-H values are between 7 (in F2OKr···HZnCN) and 67 cm-1 (in F2OXe···HMgCH3). It is noteworthy that such a blue shift of the νM-H is not consistent with the elongation of the H–M bond due to complexation. However, this conflicting phenomenon was also reported in other σ-hole interactions like halogen-hydride 4
[52] and chalcogen-hydride [37], most likely due to a complex combination of electrostatic, charge-transfer and polarization effects between the interacting molecules. For a given Z= Kr or Xe, the amount of shift in the H-M frequency depends on the nature of the electron donating/withdrawing of the X substituent and becomes larger in the order X= CH3 > F > H > CN. The existence of aerogen-hydride bond in the F2OZ···HMX complexes can be verified by the NCI index analysis. Figure S2 of Supporting Information exhibits a plot of the reduced density gradient (RDG) versus sign (λ2)ρ of these complexes. As evident, a low-gradient spike in the low-energy, low-density region (about -0.030 au) is present, which should be correspond to the aerogen-hydride interaction in these systems. Note that in some Kr complexes, there is also an additional spike located at low-density regions, which is due to the weak electrostatic interaction between the F and M atoms in these systems. One can also see that as the strength of the Z···H interaction increases, the location of the spike has a greater deviation from zero and the shape of the spike becomes broader. This indicates that NCI analysis can be considered as a powerful method for predicting the aerogen-hydride interactions. Table 1 collects the calculated interaction energies of the OF2 Z···HMX complexes at the MP2/aug-cc-pVTZ(-PP) level. To obtain more accurate and reliable interaction energies, a single point energy was also calculated at the CCSD(T)/aug-cc-pVTZ(-PP) level. From Table 1, it is evident that the interaction energies in the Xe complexes are more negative than those of the Kr counterparts, which is consistent with the calculated electrostatic potential maximum on these atoms (Figure 1). In addition, when the electron donor varies from HBeX through HZnX to HMgX, the interaction energy of Z···H becomes more negative. The estimated MP2 interaction energies of these complexes are between -2.18 and -9.72 kcal/mol, which are smaller (less negative) than those of OF2Z···NH3 and OF2 Z···NCCH3 [30] complexes. It is also apparent that the MP2 and CCSD(T) interaction energies are consistent with each other. The largest difference in the interaction energies at both levels is about 0.4 kcal/mol which shows a deviation of less than 8% from the CCSD(T) results. This suggests that the MP2 method can be regarded as a reliable method for description of aerogen-hydride interactions. Besides, the calculated BSSE values of these complexes account for about 15-24 and 14-22 % of the uncorrected MP2 and
5
CCSD(T) interaction energies, respectively, which clearly shows that the CP correction has a small effect on the interaction energies of the aerogen-hydride bonds studied here. Results from a series of extensive studies [53-55] have recommended the use of bond functions placed between interacting monomers as an effective approach to obtain accurate intermolecular potentials of weakly bound systems. Tao and coworkers [56-61] found that an extended but only roughly optimized 3s3p2d set located in the middle of the van der Waals bond can be used in many different complexes and provide reliable results for interaction energies of complexes involving rare gas atoms. By augmenting the aug-cc-pVTZ(-PP) basis set with a set of appropriate bond functions, similar to that of Tao and coworkers [61], interaction energies of OF2Z···HMH complexes were calculated at the both MP2 and CCSD(T) levels (Table S1). Examination of these results leads to the conclusion that the use of midbond functions has a pronounce effect on the interaction energies of these systems, which is consistent with primary expectation for the role of midbond functions. Besides, these effects seem to be more important for the Xe complexes, may be due to the larger dispersion effects in these systems. Table 1 also summarizes the calculated change in Enthalpy (ΔH298) and Gibbs free energy (ΔG298) associated with the formation of the OF2Z···HMX complexes at the MP2/aug-ccpVTZ(-PP) level. It is seen that for the all complexes considered, the ΔH298 values are negative, which demonstrates that the formation of these complexes is exothermic under ambient condition. However, the positive ΔG298 values indicate that these gas phase complexes would be thermodynamically unstable at 298 K and therefore the equilibrium concentrations of these complexes will be small at this temperature. Nonetheless, the results of Table 1 indicate that the OF2Z···HMX complexes ought to be experimentally observable in the gas phase, mainly at low temperature. To understand the nature of the aerogen-hydride interactions in the title complexes, the QTAIM analysis was performed. Table 2 summarizes the electron density (ρBCP), its Laplacian (∇2ρBCP) and electron energy density (HBCP) values at the Z···H bond critical points (BCPs). It is evident that the ρBCP values at Kr···H BCPs are in the range of 0.015-0.036 au, while those of Xe···H are between 0.016 and 0.040 au. All these values are consistent with the criteria proposed by Koch and Popelier for noncovalent interactions [62]. In addition, the electron density at BCP can be usually regarded as an indicator of the strength of noncovalent interactions [63-65]. As 6
Figure 2 indicates, the calculated ρBCP values correlate exponentially with Z···H binding distances, with a squared correlation coefficient of about 0.99. The corresponding ∇2ρBCP values are always positive and are between 0.044 and 0.096 au. As Table 2 indicates, all strong Z···H interactions have a negative value of the energy density (HBCP) at the BCPs, indicating that these interactions are partly covalent in nature. Table 2 lists the calculated second-order charge-transfer energies (E(2)) and the corresponding charge-transfer values due to the formation of OF2Z···HMX complexes. It is seen that for all of the binary F2OZ:HMX complexes, the main interaction responsible for the stabilization of the complexes arises from the second-order orbital interaction of the donor σM-H * orbital of the HMX with the Z O acceptor orbital of ZOF2. The charge-transfer energies due to
this interaction are in the range of 1.31-7.64 and 1.30-8.31 kcal/mol for Kr and Xe complexes, respectively. For a given Z, the calculated E(2) values in the F2OZ···HMX complexes decrease in the order X= CH3 > H > F > CN and M= Mg > Zn ≈ Be. Moreover, accompanied with this orbital interaction, a charge of about 0.003-0.044 e is transferred from the σM-H orbital of the * Lewis base to the Z O orbital of ZOF2 molecule.
The 83Kr or 131Xe absolute chemical shieldings (σ) in the binary complexes and changes in these quantities with respect to the isolated ZOF2 molecule are reported in Table 3. The calculated σ values are in the range of 270.85-285.80 and 88.68-93.29 ppm for the Kr and Xe complexes, respectively. For both series, the formation of complex leads to a significant decrease in σ value. As expected, the Xe complexes exhibit a larger change in σ value than their Kr counterparts. Also, the nature of the substituent X in the binary complexes can influence the amount of the change in σ values. Table 3 also lists the calculated 1pJ(Z–H) spin-spin constants of the OF2 Z···HMX complexes. One can see that the
1p
J(Z–H) values range from -0.13 Hz in
F2OKr···HBeF to -0.55 Hz in F2OXe···HMgCH3 , which indicates the sensitivity of
1p
J(Z–H)
coupling constants to the nature of substituents. However, there is no correlation between the 1p
J(Z–H) values and the interaction energies, or the binding distances and change in the absolute
chemical shieldings in the binary complexes relative to the corresponding monomers. It is expected that the formation of the F2OZ···HMX complexes induces an internal electronic rearrangement within each monomer. Figure 3 indicates the electron density shifts in the F2OZ···HMgX complexes, where red and green regions show loss and gain of electron 7
density, respectively. It is evident that all these complexes exhibit almost a similar pattern, that is, a significant electron density accumulation is occurred on the H atom, while a loss in the H-M bond region. The degree of this electron density accumulation or depletion increases in the order of X= CN < F < H < CH3, which is consistent with the calculated interaction energies of these complexes (Table 1). There is also a significant loss of electron density on the σ-hole region of the Z atom, which is due to the polarization of this atom by the electric field of the negatively charged H atom of HMgX molecule. 4. Conclusion In this work, ab initio calculations were performed to investigate the possible σ-hole interactions in the binary OF2Z···HMX complexes, where (Z= Kr, Xe; M = Be, Mg, Zn and X= H, F, CN, CH3). This new type of interaction was named as the aerogen-hydride, since it involves the covalently-bonded Group 18 atoms (aerogens) as the Lewis acid. The calculated Z···H binding distances were found to be in the range of 2.375-2.623 and 2.362-2.628 Å for the KrOF2 and XeOF2 complexes, respectively. Upon the complex formation, a blue shift was found for the H–M stretch vibrations. Our results also indicated that all these gas phase complexes would be thermodynamically unstable at 298 K. However, the negative ∆H (and ΔS) values suggest that a decrease in temperature will lead to an increase in the equilibrium concentration of these species. All of the strong aerogen-hydride interactions were characterized with a negative HBCP value, indicating that these interactions are partly covalent in nature. Moreover, the stability of these aerogen-hydride complexes can be attributed partly to the transfer of electronic density * from the σM-H in the HMX to the Z O in the XeOF2 or KrOF2. Finally, the formation of
OF2Z···HMX complexes leads to a decrease in 83Kr or 131Xe absolute chemical shielding values.
8
[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]
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Figure 1. Molecular electrostatic potential map of the isolated KrOF 2 and XeOF2 molecules. Color range, in kcal/mol, is: red > 40.9; 20.0 < yellow < 40.9; 0 < green < 20.0; blue < 0. The black and blue circles indicate the surface maxima and minima, respectively. The electrostatic potential value of σ-hole
associated with the Kr-O or Xe-O bond is given in kcal/mol.
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Figure 2. Correlation between the binding distances and electron densities at Z···H BCPs
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Figure 3. Electron density difference (±0.001 au) of F2OZ:HMgX. Red and green regions
indicate regions of decreased and increased electron densities, respectively.
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Table 1. Binding distance (Rint, Å), change of H-M bond length (∆R, Å), stretching frequency (ν, cm-1), shift of stretching frequencies (∆ν, cm-1), interaction energy (Eint, kcal/mol), change of MP 2 CCSD( T ) complex Rint ∆RH-M νM-H ∆νM-H Eint ∆H298 ∆G298 T Eint F2OKr···HBeCN 2.615 0.0015 2260 9 -2.18 -2.09 -4.07 2.40 188 F2OKr···HBeF 2.602 0.0012 2250 10 -3.01 -2.88 -5.14 0.65 265 F2OKr···HBeH 2.558 0.0026 2292 17 -4.14 -4.01 -5.52 0.24 286 F2OKr···HBeCH3 2.510 0.0038 2185 20 -4.68 -4.48 -6.68 1.76 236 F2OKr···HMgCN 2.453 0.0021 1752 23 -6.09 -5.90 -7.27 1.11 259 F2OKr···HMgF 2.439 0.0021 1741 25 -7.03 -6.88 -8.10 1.67 247 F2OKr···HMgH 2.376 0.0081 1691 38 -8.24 -8.12 -10.05 0.59 282 F2OKr···HMgCH3 2.375 0.0096 1673 41 -9.27 -9.03 -3.03 5.35 108 F2OKr···HZnCN 2.600 0.0011 2122 7 -2.20 -2.08 -3.01 5.21 109 F2OKr···HZnF 2.623 0.0009 2141 8 -2.19 -2.10 -5.56 0.65 267 F2OKr···HZnH 2.508 0.0051 2032 14 -5.01 -4.62 -7.36 3.54 201 F2OKr···HZnCH3 2.476 0.0053 2017 16 -5.61 -5.35 -3.16 3.18 149 F2OXe···HBeCN 2.628 0.0030 2241 15 -2.41 -2.33 -4.18 2.13 198 F2OXe···HBeF 2.606 0.0028 2234 18 -3.14 -2.92 -5.21 0.50 272 F2OXe···HBeH 2.567 0.0048 2287 22 -4.26 -3.95 -5.85 0.14 291 F2OXe···HBeCH3 2.536 0.0052 2166 26 -4.97 -4.60 -7.75 1.63 246 F2OXe···HMgCN 2.460 0.0071 1733 34 -6.26 -6.17 -8.45 0.83 271 F2OXe···HMgF 2.443 0.0068 1724 37 -6.97 -6.74 -10.32 1.10 269 F2OXe···HMgH 2.386 0.0121 1678 59 -8.98 -8.66 -11.43 0.30 291 F2OXe···HMgCH3 2.362 0.0121 1665 67 -9.72 -8.92 -3.22 2.67 163 F2OXe···HZnCN 2.613 0.0032 2102 13 -2.33 -2.21 -3.12 3.24 146 F2OXe···HZnF 2.626 0.0037 2125 15 -2.30 -2.18 -6.07 0.10 293 F2OXe···HZnH 2.512 0.0086 2017 24 -5.14 -4.96 -7.79 3.09 213 F2OXe···HZnCH3 2.481 0.0089 2002 30 -5.88 -5.65 -3.35 2.55 169 Enthalpy (∆H298, kcal/mol) and free energy (∆G298, kcal/mol), and a value of temperature (T, K), where ∆G is negative of F2OZ···HMX complexes
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Table 2. Topological parameters of electron density (electron density at BCP, ρBCP, its * Laplacian, ∇2ρBCP, and total electron energy density, HBCP) and calculated σM-H → Z O chargetransfer energy (E(2)) and the associated charge-transfer (qCT) of F2OZ···HMX a complex ρBCP HBCP E(2) ∇2ρBCP F2OKr···HBeCN 0.015 0.045 0.001 1.31 F2OKr···HBeF 0.016 0.047 0.001 1.49 F2OKr···HBeH 0.018 0.050 0.000 2.11 F2OKr···HBeCH3 0.021 0.052 0.000 2.50 F2OKr···HMgCN 0.025 0.056 -0.001 4.34 F2OKr···HMgF 0.027 0.057 -0.001 4.83 F2OKr···HMgH 0.034 0.062 -0.002 6.78 F2OKr···HMgCH3 0.036 0.063 -0.003 7.64 F2OKr···HZnCN 0.016 0.045 0.000 1.30 F2OKr···HZnF 0.015 0.044 0.000 1.39 F2OKr···HZnH 0.021 0.053 0.000 2.85 F2OKr···HZnCH3 0.025 0.056 -0.001 3.31 F2OXe···HBeCN 0.016 0.057 0.001 1.45 F2OXe···HBeF 0.017 0.060 0.001 1.88 F2OXe···HBeH 0.019 0.066 0.000 2.25 F2OXe···HBeCH3 0.021 0.070 0.000 2.74 F2OXe···HMgCN 0.027 0.079 -0.002 4.78 F2OXe···HMgF 0.029 0.082 -0.003 5.17 F2OXe···HMgH 0.036 0.092 -0.006 7.33 F2OXe···HMgCH3 0.040 0.096 -0.009 8.31 F2OXe···HZnCN 0.017 0.058 0.001 1.75 F2OXe···HZnF 0.017 0.055 0.001 1.80 F2OXe···HZnH 0.023 0.071 -0.001 3.20 F2OXe···HZnCH3 0.026 0.076 -0.001 3.94 a
All ρBCP, ∇2ρBCP and HBCP values in au, E(2) in kcal/mol and qCT in e.
qCT 0.003 0.004 0.005 0.006 0.010 0.011 0.016 0.019 0.003 0.004 0.007 0.008 0.004 0.005 0.007 0.008 0.017 0.018 0.032 0.044 0.005 0.004 0.009 0.012
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Table 3. 83Kr or 131Xe absolute chemical shielding (σ, ppm), corresponding change with respect to the isolated monomer (Δσ, ppm) and Z-H spin-spin constant (1PJ(Z–H), Hz) of F2OZ···HMX complexes complex F2OKr···HBeCN F2OKr···HBeF F2OKr···HBeH F2OKr···HBeCH3 F2OKr···HMgCN F2OKr···HMgF F2OKr···HMgH F2OKr···HMgCH3 F2OKr···HZnCN F2OKr···HZnF F2OKr···HZnH F2OKr···HZnCH3 F2OXe···HBeCN F2OXe···HBeF F2OXe···HBeH F2OXe···HBeCH3 F2OXe···HMgCN F2OXe···HMgF F2OXe···HMgH F2OXe···HMgCH3 F2OXe···HZnCN F2OXe···HZnF F2OXe···HZnH F2OXe···HZnCH3
σ 284.23 285.80 282.09 276.99 285.62 279.08 275.52 275.80 282.79 279.78 273.57 270.85 93.28 93.29 92.79 90.93 91.32 90.48 89.53 89.61 91.73 91.51 89.85 88.68
Δσ -2.11 -2.10 -2.67 -3.48 -4.25 -4.89 -5.58 -6.02 -2.58 -2.72 -2.90 -3.89 -3.32 -3.30 -3.80 -5.67 -5.28 -6.11 -6.99 -7.06 -4.87 -5.08 -6.74 -7.91
1P
J(Z–H) -0.14 -0.13 -0.22 -0.24 -0.20 -0.26 -0.38 -0.44 -0.16 -0.16 -0.24 -0.27 -0.17 -0.15 -0.29 -0.28 -0.24 -0.35 -0.50 -0.55 -0.24 -0.18 -0.43 -0.49
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Graphical abstract
Research highlights: 1- A σ-hole interaction between Group 18 atoms and a series of metal-hydrides molecules is reported for the first time. 2- Upon the complex formation, a blue shift is occurred for the H-M stretch vibrations. 3- An important charge-transfer interaction is associated with the formation of these complexes. 4- The formation of OF2 Z···HMX complexes leads to a decrease in chemical shielding values.
83
Kr or
131
Xe absolute
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