Theoretical Prediction of XRgCO+ Ions (X = F, Cl, and Rg = Ar, Kr, Xe

Article pubs.acs.org/JPCA

Theoretical Prediction of XRgCO+ Ions (X = F, Cl, and Rg = Ar, Kr, Xe) Debashree Manna,† Ayan Ghosh,‡ and Tapan K. Ghanty*,† †

Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre, Mumbai 400 085, India Laser and Plasma Technology Division, Beam Technology Development Group, Bhabha Atomic Research Centre, Mumbai 400 085, India

‡

S Supporting Information *

ABSTRACT: In this work we have predicted novel rare gas containing cationic molecules, XRgCO+ (X = F, Cl and Rg = Ar, Kr, Xe) using ab initio quantum chemical methods. Detail structural, stability, vibrational frequency, and charge distribution values are reported using density functional theory, second-order Møller−Plesset perturbation theory, and coupledcluster theory based methods. These ions are found to be metastable in nature and exhibit a linear geometry with C∞v symmetry in their minima energy structures, and the nonlinear transition state geometries are associated with Cs symmetry. Except for the two-body dissociation channel (Rg + XCO+), these ions are stable with respect to all other dissociation channels. However, the connecting transition states between the above-mentioned two-body dissociation channel products and the predicted ions are associated with sufficient energy barriers, which restricts the metastable species to transform into the global minimum products. Thus, it may be possible to detect and characterize these metastable ions using an electron bombardment technique under cryogenic conditions.

1. INTRODUCTION A chemical compound containing rare gas elements is one of the important subjects of extensive research interest in both theoretical and experimental research groups.1−51 After the successful preparation of the first rare gas compound, XePtF6 in 1962 by Neil Bartlett,3 many other rare gas containing compounds have been experimentally identified. In the past decade, various new rare gas molecules have been predicted,1,13,20,31−41,43,45 successfully prepared and identified in the rare gas matrices.1,2,4−12,14−17,21−30 In general, the insertion type rare gas compounds have a common formula, HRgY, where Rg is a rare gas atom and Y is an electronegative atom or group. The first argon containing neutral molecule, HArF was discovered in 2000 by Räsänen and co-workers,14 and HKrF was identified in 2002 by the same group.19 The rare gas was also found to form bonds with transition metals50,51 and with actinide atom containing molecule, CUO.27−29 As the rare gas atoms have saturated electronic configuration, it is generally believed that the positively charged ions are easier to form than the neutral rare gas molecules. In fact, cationic HeH+ and HeNe+ ions have been experimentally observed52 in gas discharge tubes before the first neutral rare gas compound was discovered. In contrast, there are a few examples of rare gas containing anionic compounds. In astrophysics and astrochemistry the HCO+ ion has great importance because it is the first polyatomic ion detected in the outer space besides the HCN molecule.53 It is also an isoelectronic counterpart of the HCN molecule and is the most abundant ion in hydrocarbon flames.54 In various gas phase environments, especially in plasmas, and terrestrial atmosphere, ionic complexes and clusters are important short-lived intermediates. They are also ideal systems for a detailed characterization of the intermolecular interaction involved in charged atomic or molecular systems. In this © XXXX American Chemical Society

work we deal with another class of isoelectronic molecular ions, XCO+, which are also important ion in atmospheric chemistry as it was speculated that FCO could participate in catalytic ozone destruction cycles.55,56 The insertion of Rg atoms in HCN molecule results in metastable HRgCN (Rg = Kr, Xe) species that have been investigated both theoretically and experimentally by Pettersson et al.6 Insertions of Rg atoms in its isoelectronic counterpart, HCO+, have also been investigated theoretically38 by our group. In this paper we report new XRgCO+ ions, which are relatively more stable as compared to the previously reported HRgCO+ 38 and HRgCN6 species. Here it is important to note that very recently, XRgCN and XRgNC classes of molecules (with X = Cl and Br), which are isoelectronic with the XRgCO+ ions, have been investigated experimentally by Khriachtchev49 and co-workers. Moreover, it has been emphasized49 that investigations of YRgY′ type molecules (with both Y and Y′ as electronegative atoms or groups) may be worthwhile to find new rare gas containing molecular species. In this context it may be noted that all the reported HRgY or YRgY′ type of species are chemically bound rather than the van der Waals (vdW) complexes, although the rare gas atoms are usually known to form vdW complexes. In this work, the optimized structures, energetics, atomic charge distributions, and characteristic vibrational frequencies of the title compounds are presented at the DFT, MP2, and CCSD(T) levels of theory. Received: October 28, 2013 Revised: November 29, 2013

A

dx.doi.org/10.1021/jp410631y | J. Phys. Chem. A XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry A

Article

2. COMPUTATIONAL DETAILS All the structures have been optimized using ab initio molecular orbital calculations with the GAMESS57 and MOLPRO 201258 softwares. Second-order Møller−Plesset perturbation theory (MP2), density functional theory (DFT) using Becke threeparameter exchange and Lee−Yang−Parr correlation (B3LYP),59,60 and the coupled-cluster theory (CCSD(T)) are employed to investigate the optimized geometrical structures of XRgCO+ ions (X = F and Cl) in their minima and transition states. We have adopted linear C∞v symmetry for the minima and the Cs symmetry for the bent transition states for the calculations. Standard 6-311++G(2d,2p) basis sets have been used for the C, O, F, Ar, and Cl atoms for all the DFT and MP2 calculations. However, for the Kr and Xe atoms energy adjusted Stuttgart effective core potentials61 have been used, corresponding to (6s6p1d1f)/[4s4p1d1f] basis sets. Aug-cc-pVTZ basis sets have been used for the C, O, F, Ar, and Cl atoms in the CCSD(T) method. DFT, MP2, and CCSD(T) methods have been used to calculate the infrared vibrational frequencies of all the XRgCO+ species (in their respective minima and transition states) to characterize the nature of the stationary point on the corresponding potential energy surface.

F−Rg and Cl−Rg bond length values have been found to be in the range, 1.748−1.905 and 2.075−2.333 Å, respectively, for the FRgCO+ and ClRgCO+ species using the CCSD(T) method. In general, these bond length values are very close with the bond-length values calculated using the MP2 method. The calculated F−Rg bond lengths are found to be shorter as compared to the F−Rg bond lengths in the previously predicted systems, e.g., FRgO−, FRgCC−, FRgBN−, and FRgBNR (R = H, CH3, CCH, CHCH2, F, and OH).30,62−64 In a similar way, the calculated Cl−Rg bond lengths in ClRgCO+ ions are found to be smaller than that in the ClRgCN molecules, which have been investigated very recently.49 These results confirm that the Rg atom interact in a stronger way with the halogen atom in the XRgCO+ cations. The F−Rg bonds are highly ionic in nature and the interaction between the fluorine and the rare gas atom is significantly electrostatic. The F−Rg bond distances in KrF2 and XeF2 were calculated to be 1.884 and 1.986 Å using the same level of theory and are in excellent agreement with the corresponding experimental values of 1.875 and 1.977 Å, respectively.64,65 Our F−Rg bond lengths are also in good agreement with the above-mentioned values. Now it is interesting to compare the X−Rg bond length in XRgCO+ with the corresponding X−Rg bond length in XRg+ species. The calculated F−Rg bond length values in the FRgCO+ ions are found to be slightly larger than that in the FRg+ ions (1.880, 1.741, and 1.641 Å at the CCSD(T) level of theory, for the FXe+, FKr+, and FAr+ species, respectively). However, the Cl− Rg bond lengths in ClRgCO+ ions are comparable to the corresponding bond lengths in the bare ClRg+ species (2.321, 2.165, and 2.064 Å at the CCSD(T) level of theory, for the ClXe+, ClKr+, and ClAr+ species, respectively).The second most important bond length is the Rg−C bond and the computed values are 2.212, 2.316, and 2.503 Å for FArCO+, FKrCO+, and FXeCO+ cations and 2.682, 2.694, and 2.823 Å for the ClArCO+, ClKrCO+, and ClXeCO+ cations, respectively. The Rg−C bond distances in FRgCO+ are lower than the Rg−C bond lengths in our previously predicted HRgCO+ system. However, the presently calculated Rg−C bond length values are larger than that in the recently investigated ClRg−CN systems.49 The calculated C−O bond lengths are almost constant irrespective of the residing Rg atom in the species. Now it will be interesting to discuss about the structural and geometrical parameters for the TS. The TS structure has been found to be bent geometry with Cs symmetry. The X−Rg−C bending mode is involved in going from minimum energy structure to the saddle point. A slight decrease in the F−Rg bond length and a reasonable increase in the Rg−C bond lengths are observed at the TS geometries as compared to that in the minima energy structures. The F−Rg−C bond angles are ∼100° whereas Cl−Rg−C bond angles are in the range, 90− 100°. TS dihedral angles are also slightly deviated from 180° for both the FRgCO+ and ClRgCO+ systems. Further, it is important to compare the R(X−Rg) and R(C− Rg) bond length values with respect to the two limits, namely, a covalent limit, Rcov[rcov(X) + rcov(Rg)], and a vdW limit, Rvdw[rvdw(X) + rvdw(Rg)]. The computed R(F−Rg) covalent limits are found to be 1.63, 1.73, and 1.97 Å for F−Ar, F−Kr, and F−Xe, respectively, and the corresponding vdW limits are 3.33, 3.49, and 3.63 Å. In a similar way, the covalent limits are found to be 2.08, 2.18, and 2.42 Å for the Cl−Ar, Cl−Kr, and Cl−Xe bonds, respectively. The corresponding vdW limits are 3.63, 3.77, and 3.91 Å. The calculated covalent limits of R(C− Rg) are found to be 1.82, 1.92, and 2.16 for Ar−C, Kr−C, and

3. RESULTS AND DISCUSSION 3.1. Structure Optimization. All the minimum energy structures, transition state geometries, and the relevant fragments are optimized using DFT, MP2, and CCSD(T) methods. The minimum energy and the transition state (TS) structures for all the XRgCO+ species considered here are singlet in their respective potential energy surfaces and almost similar in geometry irrespective of the residing rare gas or halogen atoms. The minimum energy, and the TS structures corresponding to the transformation of the XRgCO+ ions to the global minimum products (Rg + XCO+), calculated using CCSD(T) method are depicted in the Figure 1. XRgCO+ ions

Figure 1. Optimized structures of the (a) minimum energy (Cαv symmetry) and (b) transition state (Cs symmetry) of XRgCO+ (X = F, Cl and Rg = Ar, Kr, Xe) ions.

exhibit linear structure (C∞v symmetry) at the minima as obtained using different levels of theory, and the transition states are nonlinear bent structures, associated with Cs symmetry. Detail structural parameters obtained using all the three methods are reported in Tables 1 and 2 for both the minima energy and the transition state structures corresponding to the FRgCO+ and the ClRgCO+ ions, respectively. Because the CCSD(T) results are generally closer to the experimentally observed parameters, CCSD(T) results are discussed in more detail in the text; however, all the CCSD(T), DFT, and MP2 calculated values are reported in the tables. Now we discuss all the bond lengths in the XRgCO+ ions. The B



Article

Table 1. Optimized Structural Parameters (Bond Lengths R in Å, Bond Angles in Degrees) for Minima and Transition States (TS) of FRgCO+ (Rg = Ar, Kr, and Xe) Ions by DFT, MP2, and CCSD(T) Methods FArCO+ bond R(F−Rg)

R(Rg−C)

R(C−O)

θ(F−Rg−C)

θ(Rg−C−O)

a

FKrCO+

FXeCO+

methods

minima

TS

minima

TS

minima

TS

DFT MP2 CCSD(T) DFT MP2 CCSD(T) DFT MP2 CCSD(T) DFT MP2 CCSD(T) DFT MP2 CCSD(T)

1.741 1.765 1.748 2.242 2.103 2.212 1.112 1.126 1.123 180.0 180.0 180.0 180.0 180.0 180.0

a 1.636 1.640 a 3.195 3.171 a 1.133 1.130 a 99.9 100.5 a 179.7 179.6

1.797 1.788 1.786 2.339 2.265 2.316 1.113 1.127 1.123 180.0 180.0 180.0 180.0 180.0 180.0

1.741 1.724 1.741 3.440 3.373 3.345 1.120 1.133 1.131 98.3 100.1 100.1 179.0 178.9 178.9

1.931 1.923 1.905 2.556 2.505 2.503 1.114 1.129 1.124 180.0 180.0 180.0 180.0 180.0 180.0

1.894 1.888 1.879 3.733 3.651 3.611 1.121 1.134 1.131 98.2 98.7 97.6 178.9 178.1 178.6

Values are not reported due to a convergence problem.

Table 2. Optimized Structural Parameters (Bond Lengths R in Å, Bond Angles in Degrees) for Minima and Transition States (TS) of ClRgCO+ (Rg = Ar, Kr, and Xe) Ions by DFT, MP2, and CCSD(T) Methods ClArCO+ bond R(Cl−Rg)

R(Rg−C)

R(C−O)

θ(Cl−Rg−C)

θ(Rg−C−O)

ClXeCO+

ClXeCO+

methods

minima

TS

minima

TS

minima

TS

DFT MP2 CCSD(T) DFT MP2 CCSD(T) DFT MP2 CCSD(T) DFT MP2 CCSD(T) DFT MP2 CCSD(T)

2.141 2.069 2.075 2.589 2.653 2.682 1.116 1.131 1.128 180.0 180.0 180.0 180.0 180.0 180.0

2.093 2.062 2.058 3.354 3.254 3.227 1.121 1.134 1.131 89.9 108.3 107.1 173.3 177.0 177.1

2.225 2.163 2.180 2.656 2.673 2.694 1.116 1.131 1.128 180.0 180.0 180.0 180.0 180.0 180.0

2.186 2.148 2.162 3.518 3.412 3.381 1.121 1.134 1.131 95.4 105.2 104.1 176.9 178.6 178.9

2.366 2.327 2.333 2.838 2.825 2.823 1.116 1.131 1.128 180.0 180.0 180.0 180.0 180.0 180.0

2.339 2.312 2.320 3.792 3.673 3.647 1.122 1.134 1.132 98.4 102.9 101.9 179.4 179.8 179.8

Table 3. Energies (kJ mol−1) of the Various Dissociated Species Relative to the FRgCO+ (Rg = Ar, Kr, and Xe) Ions Calculated Using DFT, MP2, and CCSD(T) Methods Rg = Ar FRgCO+ Rg + FCO+ FRg+ + CO F + RgCO+ F + Rg + CO+ F+ + Rg + CO TS a

Rg = Kr

Rg = Xe

DFT

MP2

CCSD(T)

DFT

MP2

CCSD(T)

DFT

MP2

CCSD(T)

0.0 −449.4 130.9 30.9 159.2 502.2 a

0.0 −499.9 122.0 26.7 145.2 436.3 97.9

0.0 −462.1 101.4 44.2 134.9 454.8 78.5

0.0 −309.6 112.9 105.4 298.9 642.0 96.7

0.0 −336.7 106.2 118.1 308.4 599.6 84.5

0.0 −297.1 96.1 125.6 299.8 619.7 75.8

0.0 −165.8 87.7 167.1 442.8 785.8 74.7

0.0 −178.3 87.3 191.0 466.7 757.9 68.9

0.0 −131.1 84.4 199.7 465.8 785.7 67.2

Value is not reported due to a convergence problem.

covalent limits of 1.97 and 2.42 Å, respectively. This trend indicates that the interaction of the Xe atom with the halogen atom is quite strong in the XRgCO+ ions. However, F−Ar is an exception because the R(F−Ar) bond length of 1.748 Å in FArCO+ is rather larger than the corresponding covalent limit of 1.63 Å. Here it may also be noted that the C−Rg bond

Xe−C bonds, respectively, and the corresponding vdW limits are 3.58, 3.72, and 3.86 Å. It is important to note here that the R(F−Rg) values in FRgCO+ ions and the R(Cl−Rg) values in ClRgCO+ ions are very close to the corresponding covalent limits. In fact, the calculated F−Xe and the Cl−Xe bond length values of 1.905 and 2.333 Å are smaller than the corresponding C



Article

Table 4. Energies (kJ mol−1) of the Various Dissociated Species Relative to the ClRgCO+(Rg = Ar, Kr, and Xe) Ions Calculated Using DFT, MP2, and CCSD(T) Methods Rg = Ar ClRgCO+ Rg + ClCO+ ClRg+ + CO Cl + RgCO+ Cl + Rg + CO+ Cl+ + Rg + CO TS

Rg = Kr

DFT

MP2

CCSD(T)

DFT

MP2

CCSD(T)

DFT

MP2

CCSD(T)

0.0 −356.3 53.6 103.1 231.3 122.4 38.5

0.0 −405.7 37.9 86.8 205.2 53.8 18.3

0.0 −363.7 36.0 118.4 209.0 96.4 17.7

0.0 −271.4 52.2 122.6 316.2 207.4 39.3

0.0 −300.9 43.6 119.8 310.0 158.6 25.1

0.0 −254.0 41.5 144.5 318.7 206.1 24.0

0.0 −167.6 46.4 144.3 419.9 311.1 35.4

0.0 −182.7 45.7 152.5 428.3 276.8 28.8

0.0 −135.5 44.1 171.0 437.1 324.6 28.6

ing to the first dissociation channel show that the predicted ions are thermodynamically unstable as compared to the global minima products (XCO+ ion and Rg atom) and are higher in energy (462−297−131 kJ mol−1 for Ar−Kr−Xe in FRgCO+ and 363−254−135 kJ mol−1 for Ar−Kr−Xe in ClRgCO+, cations, respectively). However, these predicted ions are thermodynamically stable than the products corresponding to the other two two-body dissociation channels (XRg+ + CO and X + RgCO+). In general, among all the endothermic channels, dissociation energy values of the XRgCO+ ions corresponding to channel 2 are found to be the lowest (except FArCO+) and found to lie in the range 84−101 and 36−44 kJ/mol for the FRgCO+ and ClRgCO+ species, respectively. Moreover, there is a reversal of trend in the calculated dissociation energies for this channel; mainly, dissociation energy decreases in the series Ar− Kr−Xe in the FRgCO+ ions, although the same increases along Ar−Kr−Xe in the ClRgCO+ ions. Thus, among the FRgCO+ species, the dissociation energy is found to be the highest for the FArCO+ ion, whereas the dissociation energy is highest for the ClXeCO+ ion among the ClRgCO+ species. Smaller dissociation energy values corresponding to the dissociation of ClRgCO+ into ClRg+ and CO are clearly due to larger Rg−C bond lengths in ClRgCO+ as compared to that in the FRgCO+ species. It is also to be noted that the dissociation energy corresponding to channel 3 (X + RgCO+) has been found to be in the range 44−200 and 118−171 kJ/mol for the FRgCO+ and the ClRgCO+ ions, respectively, and to follow an increasing dissociation energy order (Ar−Kr−Xe) for both sets of ions. This trend is somewhat consistent with the calculated values of the X−Rg bond lengths, where the X−Xe bond length values are found to be smaller than the corresponding covalent limits, whereas the F−Ar bond is found to be slightly longer than the corresponding covalent limit and the length of the Cl−Ar bond is almost the same with the corresponding covalent limit. The three-body dissociation channels ((X + Rg + CO+) and (X+ + Rg + CO)) are also calculated to be endothermic in nature, which indicates that the predicted ions are more stable than the dissociated products. These channels lead to the local minima products in the corresponding potential energy surfaces. Because the XRgCO+ species are unstable with respect to their dissociation into the corresponding global minimum products (Rg + XCO+), it is important to evaluate their kinetic stability. For this purpose we have calculated the barrier heights for the transition states connecting the cations with the global minimum products for each of the species investigated here. Thus, the CCSD(T) calculated barrier heights (without any zero point energy correction) are found to be 78.5, 75.8, and 67.2 kJ mol−1 for the FArCO+, FKrCO+, and FXeCO+ ions, respectively, which indicate that all these species are metastable in nature with respect to the global minimum products and

distances are found to lie in between the two limiting values. Thus, it further confirms the existence of a strong interaction between the Rg atom with halogen and comparatively a weak interaction with the C atom in XRgCO+ ions. 3.2. Thermodynamic and Kinetic Stability. In general, rare gas insertion compounds are metastable in nature. To investigate the stability of the predicted XRgCO+ ions, energies of the cations as well as the products of the various possible decomposition channels have been calculated. The following dissociation channels are considered here to determine the kinetic and thermodynamic stability of the presently reported cations: Rg + XCO+ +

(1)

XRg + CO

(2)

XRgCO+ → X + RgCO+

(3)

X + Rg + CO+ +

Rg = Xe

X + Rg + CO

(4) (5)

The computed energies in kJ mol−1 for the various dissociation channels are reported in Tables 3 and 4, for the FRgCO+ and ClRgCO+ ions, resepectively, and a schematic diagram representing all the dissociation channels for the FRgCO+ ions is given in Figure 2. Here, we have considered

Figure 2. Schematic energy diagram for the four different dissociation channels (Rg = Ar, Kr, Xe) of FRgCO+ ions.

three two-body dissociation (channels 1−3) and two threebody dissociation (channels 4 and 5) pathways for the XRgCO+ ions. The first two-body dissociation channel results into the global minima products and the other two-body dissociation channels give rise to local minima products, on the singlet potential energy surface. The dissociation energies correspondD



Article

Table 5. Harmonic Vibrational Frequencies (cm−1) Calculated Using DFT, MP2, and CCSD(T) for FRgCO+ (Rg = Ar, Kr, and Xe) Ionsa F−Ar−CO+ normal mode F−Rg stretch Rg−C stretch C−O stretch F−Rg−C bendb Rg−C−O bendb F−Rg−C−O torsionc

F−Kr−CO+

F−Xe−CO+

minima

TS

minima

TS

606.2 (136.90) {514.9} (287.29) [466.05] 241.5 (29.38) {313.7} (66.41) [265.87] 2322.9 (7.99) {2192.4} (22.92) [2249.11]

d {775.1} (2.16) [709.73] d {123.9} (0.97) [125.27] d {2145.7} (11.93) [2189.63] d {−67.2} (2.85) [-64.52] d {102.3} (10.47) [105.00] d {116.9} (1.33) [117.51]

585.2 (88.18) {586.6} (121.72) [581.58] 218.9 (24.71) {240.7} (51.49) [223.04] 2322.7 (12.35) {2185.0} (12.65) [2248.47]

672.9 (0.21) {716.8} (3.48) [656.42] 111.8 (0.14) {115.9} (0.61) [114.50] 2257.2 (52.56) {2143.3} (13.23) [2185.59]

116.3 (4.54) {124.3} (3.90) [117.58] 300.2 (1.09) {324.5} (0.38) [304.74]

−159.2 (3.04) {−59.5} (1.88) [−56.97] 74.9 (4.10) {85.8} (4.62) [87.33] 98.3 (0.55) {109.2} (0.57) [107.66]

311.5 (0.73) {352.8} (0.40) [307.78] 124.2 (6.81) {134.6} (7.42) [121.29]

minima 590.1 (77.86) {600.9} (81.99) [611.07] 185.5 (19.42) {196.9} (35.42) [192.68] 2313.2 (22.87) {2176.6} (4.28) [2241.18] 96.4 (4.17) {108.2} (3.48) [107.22] 269.8 (0.29) {286.0} (0.0004) [286.92]

TS 641.2 (6.54) {656.6} (9.18) [638.77] 99.7 (0.08) {104.5} (0.46) [102.48] 2251.6 (58.59) {2139.1} (15.55) [2180.81] −59.9 (1.13) {−47.9} (1.84) [−52.04] 61.9 (2.87) {72.6} (3.03) [73.82] 92.4 (0.28) {98.1} (0.46) [96.03]

a

MP2 and CCSD(T) results are given in the curly and square brackets, respectively. Corresponding IR intensity values are given in parentheses (km mol−1). bThese two modes are doubly degenerate for minima energy structure. cThis mode is absent for minima energy structures. dValues are not reported due to a convergence problem.

the Rg−C−O or X−Rg−C bending mode depending on the rare gas atom present in the corresponding system. The IR vibrational F−Rg and Cl−Rg stretching frequencies are in the range 514.9−600.9 and 474.3−390.1 cm−1 along the Ar−Kr− Xe series using MP2 method. The Rg−C stretching frequency values are found to be lower than the X−Rg stretching frequencies and lie in the range 313.7−196.9 and 134.2−132.9 cm−1 for the FRgCO+ and ClRgCO+ ions, respectively. Here it may be noted that there is a significant change in the Rg−C stretching frequency from Ar to Xe in the case of FRgCO+ ion, whereas for ClRgCO+ it is almost the same for all. This trend is found to be consistent with the calculated Rg−C bond lengths in FRgCO+ and ClRgCO+ ions and the two body dissociation energy values corresponding to the dissociation of XRgCO+ species into XRg++ CO. Irrespective of the rare gas atom, the C−O stretching frequencies are almost comparable for both the FRgCO+ (2192.4−2176.6 cm−1) and ClRgCO+ (2161.3− 2162.9 cm−1) ions. Now it would be of interest to compare the X−Rg stretching frequencies in the XRgCO+ species with that in the bare XRg+ ions. Thus the CCSD(T) computed X−Rg stretching vibrational frequency values are 466.1, 581.6, 611.1 and 429.7, 385.0, 370.3.cm−1, respectively, along the series Ar−Kr−Xe for the FRgCO+ and ClRgCO+ cations, respectively. These values are quite different compared to the frequency values of bare F−Rg+ (706.5, 655.1, 635.2 cm−1along the series Ar−Kr−Xe) and Cl− Rg+ (449.9, 405.0, 379.7 cm−1along the series Ar−Kr−Xe) ions. The changes in the X−Rg stretching frequencies from the bare ion to the corresponding XRgCO+ cations are found to be significant in case of FRgCO+ cations. However, Cl−Rg stretching frequencies are found to remain comparatively insensitive. These trends in the change of X−Rg frequencies are consistent with the change in the calculated values of the X−Rg bond lengths in going from the bare XRg+ ion to the XRgCO+ cations, as discussed in section 3.1. The calculated Rg−C frequency values are found to be larger in the FRgCO+ species as compared to that in the ClRgCO+ ions. This trend agrees with the Rg−C bond length and the corresponding dissociation energies of channel 3 (XRg+ + CO) for the two series of species, FRgCO+ and ClRgCO+. Also, trends in the variation of the Rg−C frequencies in the FRgCO+ and ClRgCO+ ions can be rationalized in terms of the X−Rg interaction strengths, which certainly influence the Rg−C

might be possible to observe experimentally. However, the ClRgCO+ ions have relatively small barrier heights as compared to the FRgCO+ ions. Barrier heights for the ClArCO+, ClKrCO+, and ClXeCO+ ions are 17.7, 24.0, and 28.6 respectively. Here, it may be noted that the DFT calculated barrier heights for all the ions are slightly higher than the corresponding CCSD(T) values. For determining an accurate barrier height value, zero-point energy correction is another important parameter to be considered. Thus, we have also calculated the zero-point correction energies for the barrier heights and the corresponding values are found to be 4.37 (---), 4.51 (4.42), and 4.03 (4.13) kJ mol−1 for FArCO+, FKrCO+, and FXeCO+ ions and 2.67 (2.22), 2.58 (2.40), and 2.55 (2.40) kJ mol−1 for ClArCO+, ClKrCO+, and ClXeCO+ ions, respectively, using the DFT (MP2) method, which imply that the zero-point energy corrected barrier heights are sufficiently high for these cations to be identified experimentally. 3.3. Analysis of Harmonic Vibrational Frequencies. The harmonic vibrational frequency values calculated using DFT, MP2, and CCSD(T) methods for all the minimum energy and transition state structures are reported in Tables 5 and 6. Intensity values using DFT and MP2 methods are also given in Tables 5 and 6. In general, for rare gas insertion compounds, ab initio based methods such as MP2 and CCSD(T) predict frequency values are closer to the experimental ones.9,42,45,47 In view of this for further discussions we have considered mainly MP2 and CCSD(T) values. The real vibrational frequency values obtained for all the minima energy structures indicate that all these species are true minima in their respective potential energy surfaces corresponding to the C∞v symmetry. However, the presence of only one negative frequency value corresponding to the F−Rg−C bending mode for the transition state structures confirm the saddle point nature of these TS geometries associated with Cs symmetry. The computed vibrational frequencies are defined corresponding to their normal modes of vibrations such as stretch, bend, and torsion modes. Three stretching and two doubly degenerate bending modes are found for the predicted minima energy structures. The MP2 vibrational frequencies are found to be in the range of 108−2192 and 61−2161 cm−1 for minima energy FRgCO+ and ClRgCO+ ions, respectively. The highest frequency value is associated with the C−O bond stretching; however, the lowest frequency value is due to either E


TS

Cl−Rg−C−O torsionc

Rg−C−O bendb

Cl−Rg−C bendb

C−O stretch

Rg−C stretch

Article

interactions in the two series of ions. In the case of FRgCO+ ions, F−Rg interaction is strongly modified in going from Ar to Xe; however, the corresponding Cl−Rg interaction in ClRgCO+ ion remains rather insensitive, which can be interpreted in terms of the rather different nature of the F and Cl atoms in the two classes of ions. The more soft and polarizable nature of the Cl atom is somewhat unable to modify the Cl−Rg interaction considerably enough to compare it with the corresponding F−Rg interaction. The IR vibrational frequency value calculated using the CCSD(T) method for CO is 2143.3 (experimental value 2143) cm−1. This value is significantly changed in FRgCO+ (2249−2241 cm−1) and ClRgCO+ (2205−2212 cm−1) ions due to the formation of new chemical bonds. These predicted vibrational frequency values can be used to characterize the FRgCO+ and ClRgCO+ ions by spectroscopic techniques. Here it is interesting to compare the stretching frequency value of the CO fragment before and after the insertion of an Rg atom into the XCO+ ion. The C−O stretching frequencies are 2460.6 and 2272.7 cm−1 correspondingy to the FCO+ and ClCO+ ions. Thus, it is clearly evident that there is a blue shift from the bare CO stretching frequency value to the corresponding values for the XRgCO+ or XCO+ ions. A similar kind of blue shifting has been found for other rare gas compounds, such as HRgBF+ species, reported very recently by us.41 The extent of blue shifting is found to be more in the case of FRgCO+ ions as compared to that in the ClRgCO+ ions. Moreover, the amount of blue shifting can be qualitatively correlated in terms of the Rg−C interaction strengths (bond length as well as the corresponding dissociation energies) in the two series of ions, FRgCO+ and ClRgCO+. We have also performed an analysis of the normal modes in terms of their corresponding individual internal coordinates using the Boatz and Gordon methodology,66 and the results are reported in Tables 7 and 8. From Tables 5−8, it is evident that coupling of the X−Rg and the C−O stretching modes with other modes is almost negligible. However, a considerable amount of coupling with each other has been found for the Rg−C stretching and X−Rg−C and Rg−C−O bending modes. Here it may be noted that analysis of the IR vibrational frequencies of these types of ions usually shows strong coupling of some of the normal modes with each other. 3.4. Charge Distribution Analysis. Charge redistribution during formation of any species from its corresponding atoms or fragments is an important criterion to get information about the nature of bonding that exists between them. For this purpose, we have reported the computed partial atomic charges as obtained from the Mulliken population analysis using DFT and MP2 methods in GAMESS for all the ions studied here in Tables SI and SII, Supporting Information. Here it may be noted that charge values obtained using two different methods are rather similar except very few cases. Here we have considered MP2 calculated charge values for further discussions. For the FRgCO+ cations partial atomic charges on F atom are negative and oxygen acquires small positive charges as the electronegativity of the F atom is greater than that of the O atom. However, in the case of ClRgCO+ cations partial atomic charges on Cl atom are positive and small negative charges are reported on the O atom as O is more electronegative than Cl. The positive charge mainly resides on the Rg atom for both the cases. This suggests that significant reorganization of charge has taken place during the formation of XRgCO+ species from X− CO+. The atomic charges on FCO+ and ClCO+ are calculated

a MP2 and CCSD(T) results are given in the curly and square brackets, respectively. Corresponding IR intensity values are given in parentheses (km mol−1). bThese two modes are doubly degenerate for minima energy structure. cThis mode is absent for minima energy structures.

349.7 (11.73) {390.1} (9.79) [370.34] 139.5 (24.18) {132.9} (33.59) [134.87] 2290.1 (35.59) {2162.9} (0.004) [2212.54] 58.7 (0.14) {61.8} (0.08) [59.86] 189.2 (0.72) {196.0} (0.03) [191.49]

minima TS minima

354.5 (13.91) {413.0} (6.03) [385.00] 155.5 (28.35) {137.9} (43.64) [140.66] 2292.2 (31.53) {2164.8} (0.003) [2211.3] 66.6 (0.10) {68.1} (0.02) [64.13] 195.8 (1.24) {200.7} (0.06) [188.05]

TS minima normal mode

Cl−Rg stretch

386.5 (39.74) {474.31} (5.79) [429.71] 161.8 (26.6) {134.2} (46.81) [134.62] 2287.5 (38.26) {2161.3} (0.90) [2205.07] 76.2 (0.60) {75.4} (0.26) [68.60] 191.9 (0.80) {189.4} (0.05) [178.90]

393.9 (45.14) {482.7} (17.93) [456.85] 105.7 (0.07) {111.2} (0.61) [110.80] 2252.2 (113.79) {2140.9} (16.13) [2182.36] −28.9 (0.46) {−36.2} (0.65) [−38.51] 75.2 (2.49) {89.1} (6.15) [91.39] 97.9 (0.18) {103.6} (0.53) [101.77]

383.1 (8.74) {427.8} (8.33) [407.72] 101.2 (0.07) {107.1} (0.46) [104.60] 2250.9 (61.40) {2140.1} (16.45) [2180.17] −28.1 (0.28) {−33.0} (0.26) [−32.19] 66.6 (2.86) {77.6} (3.08) [79.96] 94.3 (0.05) {99.9} (0.36) [96.38]

Cl−Xe−CO+ Cl−Kr−CO+ Cl−Ar−CO+

Table 6. Harmonic Vibrational Frequencies (cm−1) Calculated Using DFT, MP2, and CCSD(T) for ClRgCO+ (Rg = Ar, Kr, and Xe) Ionsa

367.9 (1.45) {402.5} (0.59) [380.80] 92.4 (0.05) {98.6} (0.37) [95.57] 2247.1 (63.29) {2137.2} (18.10) [2176.72] −25.4 (0.15) {−29.0} (0.16) [−29.27] 56.1 (1.97) {68.5} (2.12) [67.75] 85.6 (0.03) {91.9} (0.30) [87.46]


F



Article

Table 7. DFT and MP2 Calculated Values of the Harmonic Vibrational Frequencies (cm−1) Corresponding to Individual Internal Coordinates in the FRgCO+ (Rg = Ar, Kr, and Xe) Ions FArCO+

FKrCO+

FXeCO+

internal coordinate

DFT

MP2

DFT

MP2

DFT

MP2

F−Rg stretch Rg−C stretch C−O stretch F−Rg−C bend (doubly degenerate) Rg−C−O bend (doubly degenerate)

601.1 366.1 2307.8 248.9 224.6

517.9 427.4 2172.4 285.1 247.6

595.4 333.1 2309.1 221.9 233.1

588.9 347.6 2170.0 241.2 250.1

590.8 288.9 2302.4 184.7 219.0

601.9 295.9 2165.0 200.6 230.8

Table 8. DFT and MP2 Calculated Values of the Harmonic Vibrational Frequencies (cm−1) Corresponding to Individual Internal Coordinates in the ClRgCO+ (Rg = Ar, Kr, and Xe) Ions ClArCO+

ClKrCO+

ClXeCO+

internal coordinate

DFT

MP2

DFT

MP2

DFT

MP2

Cl−Rg stretch Rg−C stretch C−O stretch Cl−Rg−C bend (doubly degenerate) Rg−C−O bend (doubly degenerate)

379.7 265.1 2279.0 125.6 163.8

473.1 219.1 2154.6 115.1 168.2

353.4 255.3 2283.4 116.6 170.8

414.0 224.3 2157.4 113.5 179.0

349.8 234.8 2282.3 106.3 167.1

390.7 217.6 2155.9 108.1 174.8

Table 9. DFT and MP2 Calculated Values of the Mulliken and NBO Charges in FRgCO+ (Rg = Ar, Kr, and Xe) Ions Using 6311++G(2d,2p) Basis Sets with the MOLPRO Program FArCO+ atom charge q(Cl) q(Rg) q(C) q(O)

DFT MP2 DFT MP2 DFT MP2 DFT MP2

FKrCO+

FXeCO+

Mulliken

NBO

Mulliken

NBO

Mulliken

NBO

−0.097 −0.162 0.775 0.791 0.291 0.296 0.031 0.075

−0.159 −0.217 0.801 0.803 0.638 0.599 −0.280 −0.186

−0.197 −0.216 0.968 0.999 0.204 0.161 0.025 0.056

−0.291 −0.308 1.003 1.025 0.571 0.491 −0.283 −0.206

−0.273 −0.288 1.102 1.140 0.166 0.115 0.004 0.033

−0.412 −0.425 1.189 1.222 0.483 0.430 −0.261 −0.227

Table 10. DFT and MP2 Calculated Values of the Mulliken and NBO Charges in ClRgCO+ (Rg = Ar, Kr, and Xe) Ions Using 6311++G(2d,2p) Basis Sets with the MOLPRO Program ClArCO+ atom charge q(Cl) q(Rg) q(C) q(O)

DFT MP2 DFT MP2 DFT MP2 DFT MP2

ClKrCO+

ClXeCO+

Mulliken

NBO

Mulliken

NBO

Mulliken

NBO

0.292 0.341 0.526 0.586 0.193 0.081 −0.011 −0.008

0.302 0.352 0.508 0.575 0.538 0.380 −0.348 −0.307

0.124 0.137 0.727 0.783 0.159 0.076 −0.010 0.003

0.158 0.174 0.676 0.736 0.511 0.383 −0.344 −0.293

0.008 0.008 0.870 0.915 0.146 0.084 −0.024 −0.006

0.0095 0.0002 0.854 0.909 0.446 0.379 −0.310 −0.289

a charge of 0.797, 0.950, and 1.035, respectively, in FRgCO+ and 0.657, 0.727, and 0.706, respectively, in ClRgCO+ ions. Generally, electron transfer is a maximum in the case of a Xe atom, which is clearly due to the less electronegative nature of xenon as compared to other rare gas atoms. Now it is of interest to compare the cumulative charge value on the FRg+ fragment in FRgCO+ species with that in the bare FRg+ ion. The total accumulated charges of the FRg+ moiety are 0.749, 0.829, and 0.882 for FAr+, FKr+, and FXe+ fragments, respectively, in FRgCO+ ions, as compared to the ideal value of unity in the bare FRg+ ion. However, in the case of ClRgCO+ species, charges on the ClRg+ moiety are 0.999, 0.920, and 0.968 for the ClAr+, ClKr+, and ClXe+ fragments, respectively, which are

as qF = 0.117, qC = 0.633, qO = 0.250 and qCl = 0.680, qC = 0.125, qO = 0.195, respectively, using the MP2 method. After the insertion of the Rg atom the qF value becomes negative and changes from +0.117 to −0.119, −0.168, and −0.190 in FArCO+, FKrCO+, and FXeCO+ ions, respectively. A similar trend has been observed for the ClRgCO+ ions. The decrease of positive charge value on carbon atom is prominent in the case of FRgCO+ ions whereas this change is negligible for the ClRgCO+ ions. As for X and C centers, a decrease in positive charge has also been observed on the O center for both the FXeCO+ and ClRgCO+ ions. Thus, after the insertion of a Rg atom into the XCO+ ion, the charge distribution has been changed drastically. The rare gas atoms, Ar, Kr, and Xe acquire G



a 0.074 (0.076) 0.0061 (−0.028) 0.067 (0.071) a 0.051 (0.049) 0.101 (0.108) 0.0291 (0.0291) −0.102 (−0.110) −0.013 (−0.021) −0.036 (−0.051) 0.0005 (0.0003) a

Due to a numerical problem, it has not been possible to obtain the BCP values for the F−Xe bond.

(0.078) (0.097) (0.046) (0.088) 0.072 0.098 0.068 0.085 (0.169) (0.076) (0.122) (0.031) 0.170 0.065 0.108 0.033 −0.056 (−0.047) −0.012 (−0.027) −0.0311 (−0.047) 0.0008 (0.0014) (0.392) (0.118) (0.100) (0.084) 0.342 0.112 0.117 0.085 (0.154) (0.092) (0.119) (0.027) 0.169 0.068 0.103 0.032

Ed (au) ∇2ρ (e a0−5) bond

ρ (e a0−3)

∇2ρ (e a0−5)

Ed (au)

ρ (e a0−3)

∇2ρ (e a0−5)

Ed (au)

ρ (e a0−3)

XXeCO+ XKrCO+ XArCO+

Table 11. DFT (MP2) Calculated Values of the BCP Properties of the X−Rg And Rg−C Bonds in XRgCO+ (X = F, Cl and Rg = Ar, Kr, and Xe) Ions H

F−Rg Rg−C (FRgCO+) Cl−Rg Rg−C (ClRgCO+)

closer to the charge value of unity in the bare ClRg+ ion. This indicates that there are more charge redistributions in the case of FRgCO+ ions as compared to the ClRgCO+ ions. Thus, from all these charge redistribution data it is clearly evident that significant charge redistribution has taken place in XRgCO+ ions after its formation from the constituent fragments. In transition states the total charge on CO is almost zero and XRg+ acquires one unit of positive charge. As the Mulliken population analysis has considerable basis set dependency, we have also performed NBO calculations for the minimum energy structures using the MOLPRO program. The DFT and MP2 calculated NBO charges for the FRgCO+ and ClRgCO+ are reported in Tables 9 and 10, respectively. For the purpose of comparison, we have also calculated the Mulliken populations using MOLPRO program. As the xenon has the smallest electronegativity value, it has the highest positive charge in both methods and both the population analysis. In all the cases, the XRg fragment contains a maximum amount of positive charge (range) in both the Mulliken and NBO schemes. However, individual atomic charges vary from the Mulliken to the NBO method. In particular, charges on the individual atoms in the CO fragment differ significantly as obtained using the Mulliken and NBO methods; however, net charges on the CO fragment are similar for both the methods. A similar trend has been found for the BF fragment in the HRgBF+ systems, reported recently.41 It is to be noted here that the net amount of MP2 NBO charge on the FRg+ fragment is smaller (0.586, 0.717, and 0.797 for FAr+, FKr+, and FXe+, respectively) than that on the ClRg+ fragment (0.827, 0.910, and 0.909 for FAr+, FKr+, and FXe+, respectively). A similar trend has also been found with the Mulliken calculated charges. The quantitative charge separation data predict that the XRgCO+ ions may be represented as [XRg+]CO. Moreover, a careful inspection of the X−Rg bond lengths and the frequencies in the bare XRg+ and XRgCO+ species reveal that the properties of the bare XRg+ are almost retained for the FXeCO+ and all the ClRgCO+ species. However, deviation is found to be the highest for the FArCO+ species, whereas the behavior of FKrCO+ species is found to be somewhat closer to that of the FXeCO+ system. This difference in the charge distribution trend is also reflected in the dissociation energy trend for channel 2 and channel 3. Chennel 3 has been found to be the lowest energy endothermic dissociation channel for the FArCO+ system, and channel 2 becomes the lowest energy for endothermic dissociation channel for all the ClRgCO+ species. In addition to the charge analysis, it is also interesting to investigate the bond critical point (BCP) properties within the framework of quantum theory of atoms-in-molecule (AIM) approach.67 Electron density based topological parameters, such as the electron density [ρ], Laplacian of the electron density [∇2ρ], and the local energy density values (Ed) obtained from AIM calculations are quite helpful in understanding the nature of a chemical bond. Thus we have calculated these parameters for the X−Rg and Rg−C bonds present in the XRgCO+ species using the AIMPAC program,67 and the values are reported in Table 11. The reported values in Table 11 clearly indicate that all the X−Rg bonds are associated with a positive value of the ∇2ρ at the BCPs and the calculated ρ values are 0.169 and 0.170 for the F−Ar and F−Kr and 0 103, 0.108, and 0.101 for the Cl−Ar, Cl−Kr, and Cl−Xe bonds, respectively. Positive ∇2ρ values clearly suggest that all the X− Rg bonds are ionic in nature. However, considerably high ρ values in BCP confirm the presence of weak covalent character

a −0.010−0.014 −0.041 (−0.051) −0.0002 (−0.0008)

Article



■

in these bonds. Similarly, positive ∇2ρ values at the BCPs of the Rg−C bonds indicate that the nature of the bonding between the XRg and CO+ moieties in the XRgCO+ species are of iondipole type with strong ionic character. The local electron density (Ed(r)) is another interesting quantity in the AIM analysis and can be defined as Ed(r) = G(r) + V(r), where G(r) and V(r) are the local kinetic and potential energy densities, respectively. The sign of Ed(r) indicates whether accumulation of electron density at a given point r is stabilizing [Ed(r) < 0] or destabilizing [Ed(r) > 0]. A negative value of Ed(r) means that V(r) dominates over G(r) and the electron density accumulation in the bond region is favorable. The calculated negative Ed(r) values at the BCPs for the F−Rg and Cl−Rg bonds clearly indicate that all these bonds are to some extent covalent in nature. However, Rg−C bonds are associated with small negative or some cases slightly positive Ed(r) values. The calculated charge distribution values and the AIM properties are found to be consistent with the calculated bond length data.

ACKNOWLEDGMENTS The authors thank the Computer Division, BARC, for providing computational facilities and support. We thank Dr. S. K. Ghosh, Dr. A. K. Nayak, Dr. A. K. Das, Dr. B. N. Jagatap, and Dr. L. M. Gantayet for their kind interest and continuous encouragements.

■

ASSOCIATED CONTENT

S Supporting Information *

Table SI of DFT (MP2) calculated values of the mulliken atomic charges in FRgCO+ (Rg = Ar, Kr, and Xe) ions. Table SII of DFT (MP2) calculated values of the mulliken atomic charges in ClRgCO+ (Rg = Ar, Kr, and Xe) ions. This material is available free of charge via the Internet at http://pubs.acs.org.

■

REFERENCES

(1) Gerber, R. B. Formation of Novel Rare-Gas Molecules in LowTemperature Matrices. Annu. Rev. Phys. Chem. 2004, 55, 55−78. (2) Pettersson, M.; Khriachtchev, L.; Lundell, J.; Räsänen, M. In Inorganic Chemistry in Focus II; Meyer, G., Naumann, D.,Wesemann, L., Eds.; Wiley-VCH: New York, 2005; p 15. (3) Bartlett, N. Xenon hexafluoro platinate(V) Xe+[PtF6]−. Proc. Chem. Soc. 1962, 218. (4) Pettersson, M.; Lundell, J.; Räsänen, M. Neutral Rare-Gas Containing Charge-Transfer Molecules in Solid Matrices. I. HXeCl, HXeBr, HXeI, and HKrCl in Kr and Xe. J. Chem. Phys. 1995, 102, 6423−6431. (5) Pettersson, M.; Lundell, J.; Räsänen, M. Neutral Rare-Gas Containing Charge-Transfer Molecules in Solid Matrices. II. HXeH, HXeD, and DXeD in Xe. J. Chem. Phys. 1995, 103, 205−210. (6) Pettersson, M.; Lundell, J.; Khriachtchev, L.; Räsänen, M. Neutral Rare-Gas Containing Charge-Transfer Molecules in Solid Matrices. III. HXeCN, HXeNC, and HKrCN in Kr and Xe. J. Chem. Phys. 1998, 109, 618−625. (7) Pettersson, M.; Lundell, J.; Khriachtchev, L.; Isoniemi, E.; Räsänen, M. HXeSH, the First Example of a Xenon-Sulfur Bond. J. Am. Chem. Soc. 1998, 120, 7979−7980. (8) Pettersson, M.; Lundell, J.; Räsänen, M. New Rare-GasContaining Neutral Molecules. Eur. J. Inorg. Chem. 1999, 729−737. (9) Pettersson, M.; Khriachtchev, L.; Lundell, J.; Räsänen, M. A Chemical Compound Formed from Water and Xenon: HXeOH. J. Am. Chem. Soc. 1999, 121, 11904−11905. (10) Evans, C. J.; Lesarri, A.; Gerry, M. C. L. Noble Gas-Metal Chemical Bonds. Microwave Spectra, Geometries, and Nuclear Quadrupole Coupling Constants of Ar-AuCl and Kr-AuCl. J. Am. Chem. Soc. 2000, 122, 6100−6105. (11) Evans, C. J.; Gerry, M. C. L. The Microwave Spectra and Structures of Ar−AgX (X = F, Cl, Br). J. Chem. Phys. 2000, 112, 1321−1329. (12) Evans, C. J.; Gerry, M. C. L. Noble Gas−Metal Chemical Bonding? The Microwave Spectra, Structures, and Hyperfine Constants of Ar−CuX (X = F, Cl, Br). J. Chem. Phys. 2000, 112, 9363−9374. (13) Lundell, J.; Chaban, G. M.; Gerber, R. B. Combined ab initio and Anharmonic Vibrational Spectroscopy Calculations for Rare Gas Containing Fluorohydrides, HRgF. Chem. Phys. Lett. 2000, 331, 308− 316. (14) Khriachtchev, L.; Pettersson, M.; Runeberg, N.; Lundell, J.; Räsänen, M. A Stable Argon Compound. Nature (London) 2000, 406, 874−876. (15) Evans, C. J.; Rubinoff, D. S.; Gerry, M. C. L. Noble Gas-Metal Chemical Bonding: The Microwave Spectra, Structures and Hyperfine Constants of Ar-AuF and Ar-AuBr. Phys. Chem. Chem. Phys. 2000, 2, 3943−3948. (16) Reynard, L. M.; Evans, C. J.; Gerry, M. C. L. Microwave Spectrum, Structure, and Hyperfine Constants of Kr−AgCl: Formation of a Weak Kr−Ag Covalent Bond. J. Mol. Spectrosc. 2001, 206, 33−40. (17) Walker, N. R.; Reynard, L. M.; Gerry, M. C. L. The Microwave Spectrum and Structure of KrAgF. J. Mol. Struct. 2002, 612, 109−116. (18) Christe, K. O. A Renaissance in Noble Gas Chemistry. Angew. Chem., Int. Ed. 2001, 40, 1419−1421. (19) Nemukhin, A. V.; Grigorenko, B. L.; Khriachtchev, L.; Tanskanen, H.; Pettersson, M.; Räsän en, M. Intermolecular Complexes of HXeOH with Water: Stabilization and Destabilization Effects. J. Am. Chem. Soc. 2002, 124, 10706−10711.

4. CONCLUSION In this present work we have proposed a novel rare gas containing insertion compounds, XRgCO+, within the framework of various ab initio quantum chemical methods. DFT, MP2, and CCSD(T) methods have been used to explore the structure, harmonic vibrational frequencies, energetic stability, and charge redistribution of these ions for the minima and the transition states. The bond lengths for all the species are closer to the covalent limit for the associated atoms. Although these species are metastable in nature as compared to the global dissociated products (XCO+ + Rg), these ions are kinetically stable and associated with high energy barriers. In fact, barrier heights are significantly high for the ions with fluorine atom. Moreover, it is found that the predicted ions are thermodynamically stable with respect to other two two-body dissociation channel (XRg+ + CO), (X + RgCO+) and two three-body dissociation channels, (X + Rg + CO+) and (X+ + Rg + CO). It is evident from the calculated bond lengths and charge distribution data that the XRgCO+ species may be better represented as [XRg+]CO. The calculated bond length values, vibrational frequency results, charge distributions data, and AIM properties clearly indicate that the Rg atom interact in a stronger way with F atom in the FRgCO + cations. Thermodynamic stability with respect to four dissociation channels and kinetic stability with respect to the dissociation path corresponding to the global minimum products clearly suggest that it might be possible to prepare and detect the XRgCO+ ions experimentally through an electron bombardment matrix isolation technique.68,69

■

Article

AUTHOR INFORMATION

Corresponding Author

*T. K. Ghanty: e-mail, [email protected]. Notes

The authors declare no competing financial interest. I



Article

HRgBF+ (Rg = He, Ar, Kr, and Xe). J. Phys. Chem. A 2013, 117, 10772−10782. (42) Lignell, A.; Khriachtchev, L.; Lundell, J.; Tanskanen, H.; Räsänen, M. On Theoretical Predictions of Noble-Gas Hydrides. J. Chem. Phys. 2006, 125, 184514. (43) Khriachtchev, L.; Räsänen, M.; Gerber, R. B. Noble-Gas Hydrides: New Chemistry at Low Temperatures. Acc. Chem. Res. 2009, 42, 183−191. (44) Lignell, A.; Khriachtchev, L. Intermolecular Interactions Involving Noble-Gas Hydrides: Where the Blue Shift of Vibrational Frequency is a Normal Effect. J. Mol. Struct. 2008, 889, 1−11. (45) Khriachtchev, L.; Isokoski, K.; Cohen, A.; Räsänen, M.; Gerber, R. B. A Small Neutral Molecule with two Noble-Gas Atoms: HXeOXeH. J. Am. Chem. Soc. 2008, 130, 6114−6118. (46) Khriachtchev, L.; Domanskaya, A.; Lundell, J.; Akimov, A.; Räsänen, M.; Misochko, E. Matrix-Isolation and ab Initio Study of HNgCCF and HCCNgF Molecules (Ng = Ar, Kr,and Xe). J. Phys. Chem. A 2010, 114, 4181−4187. (47) Khriachtchev, L.; Tapio, S.; Domanskaya, A. V.; Räsänen, M.; Isokoski, K.; Lundell, J. HXeOBr in a Xenon Matrix. J. Chem. Phys. 2011, 134, 124307. (48) Grochala, W.; Khriachtchev, L.; Räsänen, M. Noble-Gas chemistry. In Physics and Chemistry at Low Temperatures; Khriachtchev, L., Ed.; CRC Press: Boca Raton, FL, 2011; Chapter 13, p 419. (49) Arppe, T.; Khriachtchev, L.; Lignell, A.; Domanskaya, A. V.; Räsänen, M. Halogenated Xenon Cyanides ClXeCN, ClXeNC, and BrXeCN. Inorg. Chem. 2012, 51, 4398−4402. (50) Seidel, S.; Seppelt, K. Xenon as a Complex Ligand: The Tetra Xenono Gold(II) Cation in AuXe42+(Sb2F11−)2. Science 2000, 290, 117−118. (51) Hu, W.-P.; Huang, C.-H. The Intrinsic Stability of the Noble Gas-Coordinated Transition-Metal Complex Ions. J. Am. Chem. Soc. 2001, 123, 2340−2343. (52) Grandinetti, F. Helium Chemistry: a Survey of the Role of the Ionic Species. Int. J. Mass. Spectrom. 2004, 237, 243−267. (53) Buhl, D.; Snyder, L. E. Unidentified Interstellar Microwave Line. Nature (London) 1970, 228, 267. (54) Warnatz, J. In Combustion Chemistry; Gardiner, W.C., Jr., Ed.; Springer-Verlag: Berlin, 1984; p 197. (55) Wallington, T. J.; Ellermann, T.; Nielsen, O. J.; Sehested, J. Atmospheric Chemistry of FCOx, Radicals: UV Spectra and SelfReaction Kinetics of FCO and FC(O)O2 and Kinetics of Some Reactions of FCOx, with O2, O3, and NO at 296 K. J. Phys. Chem. 1994, 98, 2346−2356. (56) Knyazev, V. D.; Bencsura, Á .; Slagle, I. R. Unimolecular Decomposition of the FCO Radical. J. Phys. Chem. A 1997, 101, 849− 852. (57) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.; Jensen, J. J.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S.; Windus, T. L.; Dupuis, M.; Montgomery, J. A. General Atomic and Molecular Electronic Structure System. J. Comput. Chem. 1993, 14, 1347−1363. (58) Werner, H. -J.; Knowles, P. J.; Knizia, G.; Manby, F. R.; Schütz, M.; et al. MOLPRO, Version 2012.1, a Package of ab initio Programs. 2012, see http://www.molpro.net. (59) Becke, A. D. A New Mixing of Hartree-Fock and Local DensityFunctional Theories. J. Chem. Phys. 1993, 98, 1372−1377. (60) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785−789. (61) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Energy-adjusted ab initio Pseudopotentials for the Second and Third Row Transition Elements. Theor. Chim. Acta 1990, 77, 123−141, see http://www.theochem.uni-stuttgart.de. (62) Chen, J.-L.; Yang, C.-Y.; Lin, H.-J.; Hu, W.-P. Theoretical Prediction of New Noble-Gas Molecules FNgBNR (Ng = Ar, Kr, and Xe; R = H, CH3, CCH, CHCH2, F, and OH). Phys. Chem. Chem. Phys. 2013, 15, 9701−9709.

(20) Cohen, A.; Lundell, J.; Gerber, R. B. First Compounds with Argon−Carbon and Argon−Silicon Chemical Bonds. J. Chem. Phys. 2003, 119, 6415−6417. (21) Thomas, J. M.; Walker, N. R.; Cooke, S. A.; Gerry, M. C. L. Microwave Spectra and Structures of KrAuF, KrAgF, and KrAgBr; 83Kr Nuclear Quadrupole Coupling and the Nature of Noble Gas-Noble Metal Halide Bonding. J. Am. Chem. Soc. 2004, 126, 1235−1246. (22) Cooke, S. A.; Gerry, M. C. L. XeAuF. J. Am. Chem. Soc. 2004, 126, 17000−17008. (23) Michaud, J. M.; Cooke, S. A.; Gerry, M. C. L. Rotational Spectra, Structures, Hyperfine Constants, and the Nature of the Bonding of KrCuF and KrCuCl. Inorg. Chem. 2004, 43, 3871−3881. (24) Cooke, S. A.; Gerry, M. C. L. Insights into the Xenon−Silver Halide Interaction from a Rotational Spectroscopic Study of XeAgF and XeAgCl. Phys. Chem. Chem. Phys. 2004, 6, 3248−3256. (25) Khriachtchev, L.; Lignell, A.; Juselius, J.; Räsänen, M. Infrared Absorption Spectrum of Matrix-Isolated Noble-Gas Hydride Molecules: Fingerprints of Specific Interactions and Hindered Rotation. J. Chem. Phys. 2005, 122, 014510. (26) Michaud, J. M.; Gerry, M. C. L. XeCu Covalent Bonding in XeCuF and XeCuCl, Characterized by Fourier Transform Microwave Spectroscopy Supported by Quantum Chemical Calculations. J. Am. Chem. Soc. 2006, 128, 7613−7621. (27) Li, J.; Bursten, B. E.; Liang, B.; Andrews, L. Noble Gas-Actinide Compounds: Complexation of the CUO Molecule by Ar, Kr, and Xe Atoms in Noble Gas Matrices. Science 2002, 295, 2242−2245. (28) Andrews, L.; Liang, B.; Li, J.; Bursten, B. E. Noble Gas-Actinide Complexes of the CUO Molecule with Multiple Ar, Kr, and Xe Atoms in Noble-Gas Matrices. J. Am. Chem. Soc. 2003, 125, 3126−3139. (29) Liang, B.; Andrews, L.; Li, J.; Bursten, B. E. On the Noble-GasInduced Intersystem Crossing for the CUO Molecule: Experimental and Theoretical Investigations of CUO(Ng)n (Ng = Ar, Kr, Xe; n = 1, 2, 3, 4) Complexes in Solid Neon. Inorg. Chem. 2004, 43, 882−894. (30) Li, T.-H.; Mou, C.-H.; Chen, H.-R.; Hu, W.-P. Theoretical Prediction of Noble Gas Containing Anions FNgO− (Ng = He, Ar, and Kr). J. Am. Chem. Soc. 2005, 127, 9241−9245. (31) Lin, T. Y.; Hsu, J. B.; Hu, W. P. Theoretical Prediction of New Noble-Gas Molecules OBNgF (Ng = Ar, Kr, and Xe). Chem. Phys. Lett. 2005, 402, 514−518. (32) Ghanty, T. K. Insertion of Noble-Gas Atom (Kr and Xe) into Noble Metal Molecules (AuF and AuOH): Are they Stable? J. Chem. Phys. 2005, 123, 074323. (33) Ghanty, T. K. How Strong is the Interaction between a Noble Gas Atom and a Noble Metal Atom in the Insertion Compounds MNgF (M = Cuand Ag, and Ng = Ar, Kr, and Xe)? J. Chem. Phys. 2006, 124, 124304. (34) Jayasekharan, T.; Ghanty, T. K. Structure and Stability of Xenon Insertion Compounds of Hypohalous Acids, HXeOX [X=F, Cl, and Br]: An ab initio Investigation. J. Chem. Phys. 2006, 124, 164309. (35) Jayasekharan, T.; Ghanty, T. K. Insertion of Rare Gas Atoms into BF3 and AlF3 Molecules: An ab initio Investigation. J. Chem. Phys. 2006, 125, 234106. (36) Jayasekharan, T.; Ghanty, T. K. Significant Increase in the Stability of Rare Gas Hydrides on Insertion of Beryllium Atom. J. Chem. Phys. 2007, 127, 114314. (37) Jayasekharan, T.; Ghanty, T. K. Prediction of Metastable MetalRare Gas Fluorides: FMRgF (M = Be and Mg; Rg = Ar, Kr and Xe). J. Chem. Phys. 2008, 128, 144314. (38) Jayasekharan, T.; Ghanty, T. K. Theoretical Prediction of HRgCO+ Ion (Rg=He, Ne, Ar, Kr, and Xe). J. Chem. Phys. 2008, 129, 184302. (39) Jayasekharan, T.; Ghanty, T. K. Theoretical Investigation of Rare Gas Hydride Cations: HRgN2+ (Rg=He, Ar, Kr, and Xe). J. Chem. Phys. 2012, 136, 164312. (40) Ghosh, A.; Manna, D.; Ghanty, T. K. Theoretical Prediction of Rare Gas Inserted Hydronium Ions: HRgOH2+. J. Chem. Phys. 2013, 138, 194308. (41) Sirohiwal, A.; Manna, D.; Ghosh, A.; Jayasekharan, T.; Ghanty, T. K. Theoretical Prediction of Rare-Gas-Containing Hydride Cations: J



Article

(63) Peng, C.-Y.; Yang, C.-Y.; Sun, Y.-L.; Hu, W.-P. Theoretical Prediction on the Structures and Stability of the Noble-Gas Containing Anions FNgCC− (Ng=He, Ar, Kr, and Xe). J. Chem. Phys. 2012, 137, 194303. (64) Antoniotti, P.; Borocci, S.; Bronzolino, N.; Cecchi, P.; Grandinetti, F. Noble Gas Anions: A Theoretical Investigation of FNgBN− (Ng =He-Xe). J. Phys. Chem. A 2007, 111, 10144−10151. (65) Liao, M.-S.; Zhong, Q.-E. Chemical Bonding in XeF2, XeF4, KrF2, KrF4, RnF2, XeCl2, and XeBr2: From the Gas Phase to the Solid State. J. Phys. Chem. A 1998, 102, 10647−10654. (66) Boatz, A.; Gordon, M. S. Decomposition of Normal-Coordinate Vibrational Frequencies. J. Phys. Chem. 1989, 93, 1819−1826. (67) Bader, R. F. W. Atoms in Molecules-A Quantum Theory; Oxford University Press: Oxford, U.K., 1990. (68) Fridgen, T. D.; Parnis, J. M. Electron bombardment matrix isolation of Rg/Rg′/methanol mixtures (Rg = Ar, Kr, Xe): Fouriertransform infrared characterization of the protonbound dimers Kr2H+, Xe2H+, (ArHKr)+ and (ArHXe)+ in Ar matrices and (KrHXe)+ and Xe2H+ in Kr matrices. J. Chem. Phys. 1998, 109, 2155−2161. (69) Fridgen, T. D.; Parnis, J. M. Gas-Phase Ion Chemistry of Oxalyl Chloride: An Electron Bombardment Matrix Isolation FTIR Spectroscopic Study. J. Phys. Chem. A 1997, 101, 5117−5123.

K


Theoretical Prediction of XRgCO+ Ions (X = F, Cl, and Rg = Ar, Kr, Xe

Recommend Documents