Halogen Bonding Interaction between Fluorohalides and Isocyanides

ARTICLE pubs.acs.org/JPCA

Halogen Bonding Interaction between Fluorohalides and Isocyanides Linda J. McAllister, Duncan W. Bruce, and Peter B. Karadakov* Department of Chemistry, University of York, Heslington, York, YO10 5DD, U.K.

bS Supporting Information ABSTRACT: The optimized geometries and corresponding binding energies of complexes between fluorohalides, FX (X = Cl, Br, and I), and isocyanides, CNY (Y = CN, NC, NO2, F, CF3, Cl, Br, H, CCF, CCH, CH3, SiH3, Li, and Na), were calculated at the MP2(Full)/aug-cc-pVTZ (aug-cc-pVTZ-PP on I) level of theory, without and with basis set superposition error (BSSE) corrections through the counterpoise (CP) method. The optimized complex geometries were analyzed through the SteinerLimbach relationship, which can be used to establish correlations between the FX and XC bond lengths. For all complexes, the correlations were shown to improve considerably when using optimized geometries including BSSE corrections. It was shown that further improvements can be achieved through the introduction of an extended fourparameter form of the SteinerLimbach relationship which accounts for all differences between the valences associated with the two bonds involving the halogen in an AX 3 3 3 B complex. The results indicate that chlorine as a halogen bond donor is affected by the basicity of the isocyanides and forms different types of halogen bonds as the FCl bond lengthens in parallel with the shortening of the distance between Cl and the isocyanide carbon. This is not observed for iodine and bromine as halogen-bond donors, which is illustrated by the low levels of correlation obtained when applying the standard and extended SteinerLimbach relationships to the corresponding complexes.

’ INTRODUCTION Halogen bonding, the interaction between an area of positive electrostatic potential, dubbed the σ-hole by Politzer and coworkers,1 on a halogen atom and a Lewis base, has been attracting significant interest in recent years with applications, for example, in crystal engineering,26 liquid crystals,713 magnetic materials,14 and biological systems.15 Halogen bond strength can vary between 20 and 200 kJ mol1 with the bond strength increasing as the halogen bond donor becomes more polarizable,2 as its positive electrostatic potential increases,12 and as the Lewis base strength increases.16 Del Bene et al.17 suggested that the SteinerLimbach relationship (eq 1) ðr1 þ r2 Þ ¼ 2r02 þ ðr1 r2 Þ r01 r02 r1 þ r2 þ 2b ln 1 þ exp b ð1Þ could be employed to establish a correlation between the FCl and ClC distances (r1 and r2, respectively) in FCl:CNX complexes. This relationship has its origins in the bond-valence model used frequently when describing inorganic coordination complexes.18 Steiner and Saenger19 assumed an exponential dependence of valence on bond length to derive a precursor to eq 1 which they then applied to the distances characterizing r 2011 American Chemical Society

OH 3 3 3 O hydrogen bonds. The current form of eq 1 was derived by Limbach et al.,20 who extended the work of Steiner and Saenger to accommodate XH 3 3 3 B hydrogen bonds. The results of the MP2/aug0 -cc-pVTZ calculations for the series of FCl:CNX complexes studied by Del Bene et al.17 showed that the binding energy increased in line with the basicity of the isocyanides. The nature of the halogen bond was observed to change between complexes having traditional and chlorine-shared halogen bonds and complexes involving ion-pair halogen bonds. Values for the three empirical parameters, r01, r02, and b, included in the SteinerLimbach relationship (eq 1), were obtained through curve fitting which achieved a very good correlation (r2 = 0.994). Del Bene et al.17 reported r01 and r02 values of 1.666 and 1.651 Å, respectively, which were thought to be close to their optimized bond lengths for the isolated FCl and ClCN species (1.638 and 1.631 Å, respectively). The chlorine-shared nature of the halogen bonds in some of these complexes was observed to have an effect on the cooperative effect between halogen and hydrogen bonding in ternary complexes of the type X:CNH:Z,21 and these halogen bonds were found to have a greater stabilizing effect in comparison to lithium and hydrogen bonds. Received: July 26, 2011 Revised: August 31, 2011 Published: September 02, 2011 11079

dx.doi.org/10.1021/jp207119c | J. Phys. Chem. A 2011, 115, 11079–11086

The Journal of Physical Chemistry A The corresponding complexes with cyanides, where nitrogen is acting as the Lewis base, have also been investigated.22 In this case, only traditional halogen bonds were observed, and the absence of chlorine-shared and ion-pair halogen bonds was attributed to the higher electronegativity of nitrogen compared to carbon, making it a weaker electron donor. The aim of this paper is to perform a critical evaluation of the applicability of the SteinerLimbach relationship to the description of halogen bonding in the complexes formed between FCl, FBr, and FI and a series of isocyanides, CNY (Y = CN, NC, NO2, F, CF3, Cl, Br, H, CCF, CCH, CH3, SiH3, Li, and Na), and to derive an improved form of this relationship that takes into account the different nature of the two bonding interactions involving the halogen. The computational results provide new insights into the extent to which the halogen bond is influenced by varying the halogen bond donor.

’ METHOD Bond-Valence Model of the Halogen Bond. By analogy with the bond-valence model of the hydrogen bond, introduced by Steiner and Saenger,19 one can assume an exponential dependence of the valence si (i = 1,2) associated with each of the two bonds AX 3 3 3 B in a halogen-bonded complex on the bond length ri (see eq 2 below). r0i ri si ¼ exp ð2Þ b

Steiner and Saenger19 investigated only OH 3 3 3 O bonds, for which the parameters r0i for the two bonds in OH 3 3 3 O are identical, i.e., r01 = r02 = r0. As pointed out by Limbach et al.,20 the description of XH 3 3 3 B hydrogen bonds requires r01 and r02 which are different in value. The valences of the two bonds should add up to one (see eq 3 below). r01 r1 r02 r2 s1 þ s2 ¼ exp þ exp ¼1 ð3Þ b b This equation involves the empirical parameters r01, r02, and b and suggests a nonlinear correlation between the bond lengths r1 and r2. Solving eq 3 with respect to r2 yields eq 4 r01 r1 r2 ¼ r02 b ln 1 exp ð4Þ b which, in the case of r01 = r02 = r0, is identical to an equation derived by Steiner and Saenger.19 The SteinerLimbach relationship (eq 1) can be obtained through an alternative rearrangement of eq 3. Thus, while eqs 1 and 4 provide equally valid starting points for investigating the correlation between r1 and r2, in practice eq 1 is more straightforward to use within a nonlinear regression procedure, as the argument of the logarithmic function always remains positive, in contrast to eq 4, which requires reasonably accurate initial guesses for the parameters r01, r02, and b. While Del Bene et al.17 obtained very good correlations for a series of FCl:CNX complexes using the original Steiner Limbach relationship (eq 1), the formulation of this relationship leaves scope for improvement. Considering the substantial differences between the lengths and energies of the two bonds AX 3 3 3 B in a halogen-bonded complex, it appears appropriate to introduce specific parameters bi for each of these two bonds

ARTICLE

within the valence-bond length dependencies from eq 2, as in eq 5. r0i ri ð5Þ si ¼ exp bi With this definition of si, the sum s1 + s2 becomes (cf. eq 3) r01 r1 r02 r2 s1 þ s2 ¼ exp þ exp ¼1 ð6Þ b1 b2 and the relationship between the bond lengths r1 and r2 changes to that shown in eq 7 (cf. eq 4) r01 r1 r2 ¼ r02 b2 ln 1 exp ð7Þ b1 It is not possible to rearrange eq 6 in a form analogous to the original SteinerLimbach relationship (eq 1), i.e., a equation relating r1 + r2 to r1 r2. The introduction of an additional fourth empirical parameter (r01, r02, b1, and b2 rather than r01, r02, and b) suggests that eq 7 should provide better correlations than eqs 1 and 4, which is confirmed by the regression analyses reported in this paper. Geometry Optimization and Binding Energy Calculation. The geometries of all complexes formed between FCl, FBr, and FI and the isocyanides CNY (Y = CN, NC, NO2, F, CF3, Cl, Br, H, CCF, CCH, CH3, SiH3, Li, and Na) were optimized at the MP2(Full) level of theory using the standard aug-cc-pVTZ basis for all atoms except iodine and the aug-cc-pVTZ-PP ECP basis23 for iodine. To investigate the effect of the basis set superposition error (BSSE), the geometries of the complexes were optimized both without and with inclusion of BSSE corrections introduced through the counterpoise correction (CP) method. The geometry optimizations employed combinations of gradient and Hessian-based algorithms implemented in GAUSSIAN24 and were carried out under the “VeryTight” convergence criteria. The binding energies of the complexes were calculated from the differences between the energies of the optimized geometries of the complex (without and with CP correction) and the monomers. Curve-Fitting Procedure. The FX and XC distances from the optimized geometries were fitted to the original Steiner Limbach equation (eq 1) and the extended relationship (eq 7) using the NonLinearModel tool in Mathematica.25 The quality of the fit of the equations to the data was estimated using the coefficient of determination26 R2, defined in eq 8, the maximum absolute value of a single residual emax, and the average value of the absolute residuals eav. RSS ð8Þ TSS In this equation, RSS stands for the sum of the squares of the residuals, and TSS denotes the total sum of the squares of the deviations of the data from its mean. R2 ¼ 1

’ RESULTS AND DISCUSSION Optimized Geometries and Binding Energies. The Cartesian coordinates of the optimized geometries of the complexes are given in Table S1 in the Supporting Information. The majority of the complexes were found to have linear C∞v geometries. The exceptions to this are complexes including the isocyanides CNCF3, CNCH3, and CNSiH3, which all have C3v 11080

dx.doi.org/10.1021/jp207119c |J. Phys. Chem. A 2011, 115, 11079–11086

The Journal of Physical Chemistry A

Figure 1. MP2(Full)/aug-cc-pVTZ optimized geometries of (a) FBr: CNCl (C∞v symmetry), (b) FBr:CNNO2 (C2v symmetry), and (c) FBr: CNCH3 (C3v symmetry). The distances r1 and r2 used in the original and extended SteinerLimbach equations are shown for clarity. F in yellow, Br in red, C in orange, N in blue, H in white, Cl in green, and O in purple.

symmetry, and complexes including CNNO2, which have C2v symmetry. Schematics of examples of each of these types of complexes are shown in Figure 1. Del Bene et al.17 suggested that the type of halogen bond in complexes FCl:CNY can be characterized from the distances within the FCl 3 3 3 C fragment and the binding energy. Traditional halogen bonds occur when the chlorine is closer to the fluorine, which leads to longer FC distances, R(FCl) < R(ClC), and lower binding energies. In chlorine-shared halogen bonds, the FC distance becomes shorter, R(FCl) > R(ClC), and the binding energy increases. Finally, in ion-pair halogen bonding, where the chlorine has moved toward the carbon atom on the isocyanide, the FC distances are a little longer, but the R(FCl) R(ClC) difference and binding energies increase.21 Table 1 shows the distances in the optimized geometries of the FX:CNY complexes studied in this paper necessary for characterizing the type of halogen bond present together with the corresponding binding energies. Note that the ordering of the binding energies according to Y substituents is different for X = Cl, X = Br, and X = I. Looking at the FCl:CNY complexes, the effects of the CP correction on the optimized geometries are expressed mainly in a shortening of the FCl distance (r1) and a lengthening of the ClC distance (r2). The magnitude of these changes varies with the different types of halogen bond; it is less significant in the ionpair halogen bonds than in the traditional halogen bonds. The counterpoise correction does, however, have a large effect on the FCl:CNY binding energy, showing that taking BSSE into account is essential in these calculations. The FCl:CNY r1 and r2 distances computed without CP correction are reasonably similar to those reported by Del Bene et al.,17 with the exception of the FCl:CNNO2 complex, for which the

ARTICLE

values of r1 and r2 obtained by Del Bene and co-workers are 1.674 and 2.411 Å, respectively. The differences between the binding energies obtained in this work and those reported in ref 17 are relatively large, with the values from the previous work, in most cases, being approximately halfway between the binding energies with and without CP correction listed in Table 1. Some of the numerical differences between the current results and those of Del Bene et al.17 could be due to the slightly larger basis set employed in the current work, the possible use of a “frozen-core” MP2 [MP2(FC)] in ref 17 [against MP2(Full) in the current work], and a different choice of complex and monomer geometries when calculating the binding energies. Using the current results, it is still possible to divide the complexes into three groups exhibiting different types of halogen bonding interactions depending on the basicity of the isocyanide. As a rule, calculations including CP correction produce more reliable results for weakly bound systems; therefore, it is preferable to use CPcorrected results in the classification scheme. The complexes with r1 < r2 include FCl:CNCN, FCl:CNNC, FCl:CNF, and FCl: CNCl, with binding energies of 29.6828.64 kJ mol1. However, two other complexes with r1 > r2, FCl:CNNO2 and FCl: CNCF3, exhibit binding energies within the same range. This suggests that distinction between traditional and chlorine-shared halogen bonds should be based on structural characteristics only, as complexes involving these two types of bonds can have very similar binding energies. In the case of the FBr:CNY complexes, the CP-corrected results for r1 and r2 indicate that all of these complexes, except FBr:CNLi and FBr:CNNa, should be classified as exhibiting traditional halogen bonds. However, the differences between these bond lengths in FBr:CNLi and FBr:CNNa are very small, under 0.02 Å, which suggests that the Br 3 3 3 C bonds in these complexes are intermediate between traditional and bromineshared halogen bonds. It is interesting to observe that without the inclusion of CP corrections the FBr:CNCCH, FBr:CNCCF, FBr:CNSiH3, and FBr:CNCH3 complexes could be considered as involving the same type of intermediate halogen bond, but FBr:CNLi and FBr:CNNa would appear to exhibit traditional halogen bonds. Clearly, the explicit treatment of BSSE effects is essential for obtaining correct results concerning FBr:CNY complexes. As expected, the binding energies are larger than those in the FCl:CNY complexes and, once again, increase in line with the basicity of the isocyanides. A similar trend is observed for complexes between FI and isocyanides. Clearly, all FI:CNY complexes included in Table 1 exhibit traditional halogen bonds. Curve Fitting. The parameters in the SteinerLimbach equation (eq 4) and the extended four-parameter relationship (eq 7) were evaluated for each of the data sets obtained from the geometry optimizations. These parameters, together with the corresponding estimates of the quality of the fit, the coefficient of determination, R2, the maximum absolute residual, emax, and the average of the absolute residuals, eav, are given in Tables 2 and 3, respectively. One immediate observation from Tables 2 and 3 is that the use of optimized geometries corrected for BSSE through the CP method leads to a significant enhancement of the goodness of the fit: for example, for FCl as the halogen bond donor, in the case of the extended four-parameter relationship (eq 7), R2, emax, and eav improve from 0.883, 0.2506, and 0.0551 to 0.9997, 0.0340, and 0.0179, respectively, on passing from geometries calculated without CP corrections to geometries for which these corrections were included (see Table 3). This strongly suggests that the 11081



ARTICLE

Table 1. Distances (r1, r2, Å) and Binding Energies (ΔE, kJ mol1) of FX:CNY Complexes Calculated at the MP2(Full)/aug-ccpVTZ (aug-cc-pVTZ-PP on I) Level of Theory with and without CP Correctiona X = Cl r1

Y CN NC NO2 F CF3 Cl Br H CCF CCH CH3 SiH3 Li Na a

r2

X = Br ΔE

r1

r2

X=I ΔE

r1

r2

ΔE

1.6577

2.5301

19.55

1.8678

1.9762

38.22

1.9909

2.2159

55.24

(1.6718)

(2.3561)

(29.68)

(1.8956)

(1.8761)

(72.88)

(2.0055)

(2.1225)

(81.83)

1.6603 (1.6756)

2.5089 (2.3346)

21.16 (31.76)

1.8150 (1.8715)

2.2280 (1.9635)

36.72 (67.23)

1.9778 (1.9932)

2.3067 (2.1937)

53.36 (77.79)

1.8779

1.7411

23.39

1.8459

2.0959

38.93

1.9849

2.2864

55.25

(1.8639)

(1.6903)

(44.48)

(1.8884)

(1.9318)

(69.30)

(1.9995)

(2.1835)

(77.97)

1.6631

2.5004

23.02

1.8025

2.3360

37.69

1.9681

2.4072

52.21

(1.6739)

(2.3753)

(31.50)

(1.8309)

(2.1567)

(59.54)

(1.9774)

(2.3176)

(70.33)

1.8468

1.7192

24.29

1.8486

2.0813

41.42

1.9852

2.2853

48.89

(1.6762)

(1.8630)

(48.01)

(1.8914)

(1.9194)

(72.43)

(2.0004)

(2.1807)

(80.43)

1.6850 (1.8598)

2.3307 (1.7172)

28.64 (51.28)

1.8455 (1.8837)

2.1288 (1.9765)

49.18 (77.92)

1.9880 (2.0003)

2.3069 (2.2194)

65.40 (87.50)

1.8445

1.7672

34.40

1.8586

2.0858

53.19

1.9929

2.2902

69.13

(1.8705)

(1.7043)

(60.67)

(1.8951)

(1.9499)

(85.76)

(2.0059)

(2.2021)

(93.99)

1.8556

1.7393

36.16

1.8579

2.0863

53.19

1.9906

2.3020

68.48

(1.8756)

(1.6912)

(56.90)

(1.8935)

(1.9541)

(79.30)

(2.0023)

(2.2198)

(87.37)

1.8614

1.7198

38.72

1.8791

2.0031

54.91

2.0006

2.2394

71.24

(1.8772)

(1.6804)

(64.18)

(1.9077)

(1.9050)

(89.57)

(2.0140)

(2.1540)

(97.65)

1.8616 (1.8760)

1.7131 (1.6760)

38.57 (63.51)

1.8809 (1.9083)

1.9913 (1.8974)

54.39 (88.83)

2.0011 (2.0147)

2.2307 (2.1459)

70.72 (96.81)

1.8671

1.7522

49.50

1.8776

2.0530

66.08

2.0022

2.2812

81.42

(1.8890)

(1.7034)

(71.49)

(1.9058)

(1.9950)

(95.78)

(2.0134)

(2.2067)

(103.20)

1.8853

1.7032

53.53

1.8946

1.9862

65.42

2.0068

2.2452

79.37

(1.8995)

(1.6687)

(78.68)

(1.9205)

(1.9009)

(98.31)

(2.0192)

(2.1682)

(103.41)

1.9547

1.6995

108.61

1.9560

1.9490

114.23

2.0434

2.2184

124.78

(1.9693)

(1.6719)

(132.38)

(1.8974)

(1.9696)

(145.56)

(2.0530)

(2.1671)

(146.83)

1.9787 (1.9935)

1.6990 (1.6715)

125.59 (152.99)

1.9504 (1.8966)

1.9663 (1.9859)

129.49 (164.27)

2.0553 (2.0658)

2.2115 (2.1598)

139.12 (165.59)

Values obtained without counterpoise correction are given in parentheses.

Table 2. Parameters and R2 Values, Maximum Absolute Residuals, emax, and Averages of the Absolute Residuals, eav, for the SteinerLimbach Equation (Equation 4) Fitted to Data Obtained from Geometry Optimizations of Complexes between Halogen Bond Donors and Isocyanidesa halogen bond donor

r01/Å

r02/Å

b

R2

emax

eav

FCl

1.6318 (1.67058)

1.39994 (1.7697)

0.413033 (0.153136)

0.989 (0.870)

0.0656 (0.2906)

0.0297 (0.0522)

FBr FI a

1.78831

1.83946

0.189969

0.938

0.0671

0.0200

(1.82259)

(1.84765)

(0.115799)

(0.828)

(0.0596)

(0.0223)

1.9648

2.19011

0.0702668

0.804

0.0566

0.0155

(1.9765)

(2.15121)

(0.0429418)

(0.698)

(0.0593)

(0.0185)

Data for curves fitted to optimized geometries of complexes without CP correction of BSSE are given in parentheses.

assumptions behind the original SteinerLimbach equation (eq 4) and the extended four-parameter relationship (eq 7) are well-justified for a wide range of halogen bonds and that the explicit elimination of BSSE in the MP2-level geometry optimization procedure improves distinctly the accuracy of the predicted lengths of the bonds involving the halogen-bonded atoms, even when working with basis sets of triple-ζ quality. It can be seen from the R 2 values in Table 2 that the goodness of the fit achieved with the original three-parameter

SteinerLimbach equation (eq 4) decreases as the halogen bond donor becomes more polarizable. This trend is exemplified by the plots in Figures 2 and 3 and highlights the need for a modification to the original SteinerLimbach relationship when it is applied to halogen bonding. The plots in Figures 2 and 3 show that there is a noticeable improvement in the quality of the fit when switching from the original three-parameter SteinerLimbach equation (eq 4) to the four-parameter relationship (eq 7) for complexes with FCl as 11082



ARTICLE

Table 3. Parameters and R2 Values, Maximum Absolute Residuals, emax, and Averages of the Absolute Residuals, eav, for the Extended Four-Parameter Relationship (Equation 7) Fitted to Data Obtained from Geometry Optimizations of Complexes between Halogen Bond Donors and Isocyanidesa halogen bond donor FCl FBr FI a

r01/Å

r02/Å

b1

R2

b2

1.44176

1.65694

0.0864868

(1.65964)

(1.68683)

(0.00935658)

10.3601 (2.30372)

emax

eav

0.997

0.0340

0.0179

(0.883)

(0.2506)

(0.0551)

1.70194

1.93062

0.0517989

2.59899

0.945

0.0624

0.0186

(1.75563)

(1.88552)

(0.0393223)

(1.69762)

(0.829)

(0.0584)

(0.0223)

1.9651 (1.95469)

2.18388 (2.16091)

0.0843672 (0.0139925)

0.0664381 (0.710074)

0.804 (0.701)

0.0566 (0.0575)

0.0155 (0.0185)

Data for curves fitted to optimized geometries of complexes without CP correction of BSSE are given in parentheses.

Figure 2. Graphs showing the fits achieved with the original SteinerLimbach equation (eq 4) (a, c, e) and the four-parameter relationship (eq 7) (b, d, f) for the geometries of FCl (a, b), FBr (c, d), and FI (e, f) with isocyanides optimized without the CP correction.

the halogen bond donor. However, as the halogen bond donor becomes more polarizable, the difference between the performances of the two relationships decreases, and the improvement due to the fourth parameter becomes more modest. The reason

for this behavior is associated with the general decrease in the goodness of the fits in the series FCl, FBr, and FI (see Tables 2 and 3 and Figures 2 and 3). The additional flexibility introduced with the different b1 and b2 parameters in eq 7 is unable to 11083



ARTICLE

Figure 3. Graphs showing the fits achieved with the original SteinerLimbach equation (eq 4) (a, c, e) and the four-parameter relationship (eq 7) (b, d, f) for the geometries of FCl (a, b), FBr (c, d), and FI (e, f) with isocyanides optimized with the CP correction.

provide significantly better fits with more widely spread sets of points as in Figures 2(cf) and 3(cf), for which the R2, emax, and eav characteristics of three- and four-parameter equations become very similar. It is well-known that in the case of nonlinear regression the coefficient of determination R2 does not always provide an appropriate measure of the goodness of the fit.27 Therefore, in the current work, the R2 values were examined together with the corresponding maximum absolute residuals, emax, and the averages of the absolute residuals, eav. The data presented in Tables 2 and 3 indicate that emax and eav can be viewed as more sensitive and more reliable criteria when judging the quality of the fits utilizing the three- and four-parameter eqs 4 and 7. Despite the fact that, as mentioned earlier, the FCl:CNY results without CP correction obtained in this paper are very similar to those of Del Bene et al.,17 the fitted values of the parameters r01 and r02, corresponding to these results, 1.67058 and 1.7697 Å (see Table 2), are different from those reported in ref 17, 1.638 and 1.631 Å, respectively. In addition to this, the

coefficient of determination, R2, of 0.870 listed in Table 2 is substantially smaller than the R2 value of 0.994 in ref 17. These discrepancies are too large to be attributed to the already mentioned differences between the computational procedures. Obviously, eq 1, which correlates r1 + r2 and r1 r2 and was used by Del Bene and co-workers, produces fits which differ from those obtained using eq 4, which correlates r1 and r2 and was used in the current work. In certain cases, correlating r1 + r2 and r1 r2 can help eliminate outliers; for example, the outlier observed in Figure 2(a) is not present in Figure 1 in ref 17. However, improvements of this type are fortuitous and should not be interpreted as an indication that eq 1 performs better than eq 4. The “sum of valences” assumptions in eqs 3 and 6 suggest that the fitted values of the parameters r01 and r02 in eqs 1, 4, and 7 could be viewed as some reference FX and XC bond lengths. To compare the values of r01 and r02 to the FX and XC distances in the isolated species FX and XCN, the geometries of FX and XCN were optimized at the MP2(Full)/aug-cc-pVTZ 11084



ARTICLE

Table 4. FX and XC Bond Lengths in the Isolated Molecules FX and XCN, Optimized at the MP2(Full)/aug-ccpVTZ (aug-cc-pVTZ-PP on I) Level of Theory molecule 1

molecule 2

R(FX)/Å

R(XC)/Å

FCl

ClCN

1.6346

1.6251

FBr

BrCN

1.7511

1.7697

FI

ICN

1.9148

1.9765

(aug-cc-pVTZ-PP on I) level of theory. The optimized FX and XC bond lengths are listed in Table 4. While some of the FX and XC bond lengths from Table 4 are in good agreement with the corresponding parameters r01 and r02 in Tables 2 and 3, other bond lengths in the isolated species differ significantly from their r01 and r02 counterparts. It could prove more meaningful to compare the values of the parameters r01 and r02, calculated from correlations for groups of complexes, much larger than those studied in the current work, to the average FX and XC bond lengths taken from the optimized geometries for a wide selection of molecules containing such bonds.

’ CONCLUSIONS The halogen bonding in the complexes between fluorohalides, FX (X = Cl, Br, and I), and isocyanides, CNY (Y = CN, NC, NO2, F, CF3, Cl, Br, H, CCF, CCH, CH3, SiH3, Li, and Na), was investigated at the MP2(Full)/aug-cc-pVTZ (aug-cc-pVTZ-PP on I) level of theory, without and with basis set superposition error (BSSE) corrections, which were included through the counterpoise (CP) method. The results indicate that the CP correction influences very significantly the computed complex geometries and binding energies, which shows that taking BSSE into account is essential in calculations on such systems. The optimized complex geometries were analyzed through two forms of the SteinerLimbach relationship, which can be used to establish correlations between the FX and XC bond lengths: the original three-parameter SteinerLimbach relationship (see eqs 1 and 4) and an extended four-parameter relationship which takes into account all differences between the two bonds involving the halogen (see eq 7). For all complexes, both the three- and four-parameter correlations were shown to improve considerably when using optimized geometries including BSSE corrections. The extended four-parameter relationship was found to provide higher-quality correlations than the original three-parameter SteinerLimbach relationship, especially for complexes involving FCl. The current higher-level results support the findings of Del Bene et al.,17 according to which chlorine as a halogen bond donor is affected by the basicity of the isocyanides and forms different types of halogen bonds as the FCl bond lengthens in parallel with the shortening of the distance between Cl and the isocyanide carbon. However, as discussed in the preceding sections, the current results exhibit a number of qualitative and quantitative differences from those reported in previous work. The distinction between the different types of halogen bond, traditional, halogen-shared, and ion-pair, is well-expressed in the case of Cl as a halogen-bond donor. This distinction becomes more blurred in the case of Br, for which most studied halogen bonds were found to be traditional, and only those involving the strongest bases, CNNa and CNLi, could be thought of as intermediate between traditional and bromine-shared halogen

bonds. Finally, in the case of I, there is no distinction, and all studied halogen bonds were identified as traditional.

’ ASSOCIATED CONTENT

bS

Supporting Information. Cartesian coordinates for the optimized geometries of all FX:CNY complexes studied in this paper. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT The authors thank the EPSRC for financial support to L.J.M. ’ REFERENCES (1) Clark, T.; Hennemann, M.; Murray, J. S.; Politzer, P. J. Mol. Model. 2007, 13, 291. (2) Metrangolo, P.; Resnati, G.; Pilati, T.; Biella, S. In Halogen Bonding Fundamentals and Applications; Metrangolo, P., Resnati, G., Eds.; Springer: Berlin, 2008; Vol. 126, p 105. (3) Cavallo, G.; Biella, S.; Lu, J. A.; Metrangolo, P.; Pilati, T.; Resnati, G.; Terraneo, G. J. Fluorine Chem. 2010, 131, 1165. (4) Metrangolo, P.; Resnati, G. Science 2008, 321, 918. (5) Rissanen, K. CrystEngComm 2008, 10, 1107. (6) Metrangolo, P.; Resnati, G.; Pilati, T.; Liantonio, R.; Meyer, F. J. Polym. Sci., Part. A: Polym. Chem. 2007, 45, 1. (7) Bruce, D. W. In Halogen Bonding Fundamentals and Applications; Metrangolo, P., Resnati, G., Eds.; Springer: Berlin, 2008; Vol. 126, p 161. (8) Nguyen, H. L.; Horton, P. N.; Hursthouse, M. B.; Legon, A. C.; Bruce, D. W. J. Am. Chem. Soc. 2004, 126, 16. (9) Metrangolo, P.; Prasang, C.; Resnati, G.; Liantonio, R.; Whitwood, A. C.; Bruce, D. W. Chem. Commun. 2006, 3290. (10) Prasang, C.; Whitwood, A. C.; Bruce, D. W. Chem. Commun. 2008, 2137. (11) Prasang, C.; Nguyen, H. L.; Horton, P. N.; Whitwood, A. C.; Bruce, D. W. Chem. Commun. 2008, 6164. (12) Prasang, C.; Whitwood, A. C.; Bruce, D. W. Cryst. Growth Des. 2009, 9, 5319. (13) Roper, L. C.; Prasang, C.; Kozhevnikov, V. N.; Whitwood, A. C.; Karadakov, P. B.; Bruce, D. W. Cryst. Growth Des. 2010, 10, 3710. (14) Fourmigue, M. In Halogen Bonding Fundamentals and Applications; Metrangolo, P., Resnati, G., Eds.; Springer: Berlin, 2008; Vol. 126, p 181. (15) Parisini, E.; Metrangolo, P.; Pilati, T.; Resnati, G.; Terraneo, G. Chem. Soc. Rev. 2011, 40, 2267. (16) Wasilewska, A.; Gdaniec, M.; Polonski, T. CrystEngComm 2007, 9, 203. (17) Del Bene, J. E.; Alkorta, I.; Elguero, J. J. Phys. Chem. A 2010, 114, 12958. (18) Brown, I. D. Acta Crystallogr., Sect. B: Struct. Sci. 1992, 48, 553. (19) Steiner, T.; Saenger, W. Acta Crystallogr., Sect. B: Struct. Sci. 1994, 50, 348. (20) Ramos, M.; Alkorta, I.; Elguero, J.; Golubev, N. S.; Denisov, G. S.; Benedict, H.; Limbach, H. H. J. Phys. Chem. A 1997, 101, 9791. (21) Del Bene, J. E.; Alkorta, I.; Elguero, J. Phys. Chem. Chem. Phys. 2011, 13, 13951–13961. (22) Del Bene, J. E.; Alkorta, I.; Elguero, J. Chem. Phys. Lett. 2011, 508, 6. (23) Wood, G. P. F.; Radom, L.; Petersson, G. A.; Barnes, E. C.; Frisch, M. J.; Montgomery, J. A. J. Chem. Phys. 2006, 125. 11085



ARTICLE

(24) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Jr., J. A. M.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, € Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; S.; Daniels, A. D.; Farkas, O.; Fox, D. J.; Gaussian09, revision A.1; Gaussian, Inc.: Wallingford, CT, 2009. (25) Mathematica; 8; Wolfram: Champaign, IL, 2011. (26) Kahane, L. H. Regression Basics, 2nd ed.; Sage Publications: Los Angeles, 2008. (27) Cameron, A. C.; Windmeijer, F. A. G. J. Econometrics 1997, 77, 329.

11086


Halogen Bonding Interaction between Fluorohalides and Isocyanides

Recommend Documents