Studies on the Encapsulation of Various Anions in Different Fullerenes

ARTICLE pubs.acs.org/JPCA

Studies on the Encapsulation of Various Anions in Different Fullerenes Using Density Functional Theory Calculations and BornOppenheimer Molecular Dynamics Simulation Pawar Ravinder and Venkatesan Subramanian* Chemical Laboratory, Council of Scientific and Industrial Research, Central Leather Research Institute, Adyar, Chennai 600 020, India

bS Supporting Information ABSTRACT: The density functional theory (DFT)-based Becke’s three parameter hybrid exchange functional and LeeYangParr correlation functional (B3LYP) calculations and BornOppenheimer molecular dynamics (BOMD) simulations have been performed to understand the stability of different anions inside fullerenes of various sizes. As expected, the stability of anion inside the fullerene depends on its size as well as on the size of the fullerene. Results show that the encapsulation of anions in larger fullerenes (smaller fullerene) is energetically favorable (not favorable). The minimum size of the fullerene required to encapsulate F is equal to C32. It is found from the results that C60 can accommodate F, Cl, Br, OH, and CN. The electron density topology analysis using atoms in molecule (AIM) approach vividly delineates the interaction between fullerene and anion. Although F@C30 is energetically not favorable, the BOMD results reveal that the anion fluctuates around the center of the cage. The anion does not exhibit any tendency to escape from the cage.

’ INTRODUCTION It is well-known that the wonder molecule of the past decade is fullerene (C60). A huge volume of literature is accumulated over the years on this fascinating molecule.15 One of the important findings from the previous studies is that fullerene can form endohedral complexes by encaging atoms, ions, and small molecules.610 Numerous experimental and computational studies have been carried out to understand the chemical and physical properties of endohedral fullerenes (EF).1115 It is interesting to observe from the previous reports that the noncovalent interaction plays a major role in the stabilization of guest molecules inside the fullerene.16 The inner and outer π-surfaces of fullerene interact differently with guest molecules.17 Some of the potential applications of endohedral chemistry of fullerenes include catalysis, storage, sensing, and gas separation.1618 Fullerenes encapsulated by metal (endohedral metallofullerenes) are the most studied compounds in the field of fullerenes.1923 They exhibit some common remarkable features: (i) they are usually stable under ambient conditions, (ii) they show electronic structures basically different from those of the parent empty cages, and (iii) they are able to encapsulate metals with magnetic or radioactive properties.24 Hence, they can be exploited in a wide variety of materials science and biomedical applications. Recently, two reviews have appeared on the endohedral metallofullerenes (EMF).25,26 It is found that EMF can be divided into the following classes: (a) classical EFs of the type M@C2n and M2@C2n (M = metal, noble gas, small molecule and 60 e 2n e 88); (b) metallic nitride EMFs (M3N@C2n, M = metal and 68 e 2n e 96); r 2011 American Chemical Society

(c) metallic carbide EMFs (M2C2@C2n, M3C2@C2n, M4C2@C2n, and M3CH@C2n with M = metal and 68 e 2n e 92); (d) metallicoxide EMFs (M4O2@C2n and M4O3@C2n); and (e) metallic sulfide (M2S@C2n). To understand the interaction of incarcerated species with the fullerene, several theoretical studies have been carried out.2739 A variety of theoretical methods with different theoretical rigor have been employed to understand the structure and properties of EFs and EMFs.2739 It is noteworthy to mention here that computational studies by Cioslowski and colleagues have created significant interest among theoretical community to unravel the chemistry of EFs.2730 To gain insight into the hostguest interactions involving fullerene, the molecular electron density (MED) and molecular electrostatic potential (MESP) topography of C60 have been investigated.40 It is observed from the previous studies that the outer surface of fullerene is rich in π-electron density with positively charged nuclei inside.40 Furthermore, the electrostatic potential at the cage center is found to be positive.40 The power of double layered C60 cage attracted researchers to encage different molecules inside the fullerene. In fact, it is now established that spatial confinement of encaged molecules in a C60 exhibit different physical and chemical properties.1618 Herein, we describe some of the Received: April 12, 2011 Revised: September 5, 2011 Published: September 08, 2011 11723

dx.doi.org/10.1021/jp203421v | J. Phys. Chem. A 2011, 115, 11723–11733

The Journal of Physical Chemistry A important contributions from computational investigations on the EFS and EMFs. Cioslowski et al. have investigated endohedral complex formation of atoms, ions, and molecules with C60 using Hartree Fock method employing 431G basis set for the cage molecule and duble ξ basis set for the guest species.28 It was found that there are no changes in the structure of C60 upon encapsulation.28 In addition, endohedral complexes containing ions and polar molecules were stabilized inside the cage, whereas the complexes formed by the nonpolar or neutral molecule were destabilized relative to the separated host and guest molecules.28 Furthermore, the bond length of the guest molecule decreased and the calculated vibrational frequency increased due to the spatial confinement.28 Subsequently, several studies have been made on the encapsulation of a variety of atoms and ions inside the fullerene cages of different dimensions.2739 An ab initio study of the endohedral complexes of C60, Si60, and Ge60 with monatomic ions have been made by Geerlings and co-workers.31 They have shown that the following factors affect the endohedral complex formation: (i) endohedral electrostatic potential, (ii) the ion induced dipole interaction of the ion with the polarizable cage, and (iii) electrostatic repulsion between ion and cage electron cloud. In a subsequent work, Geerlings and colleagues have studied the reactivity of structurally confined ethylene molecule using conceptual DFT.31 Ramachandran and Sathyamurthy have investigated the effect of spatial confinement on water clusters by encapsulating them in a fullerene cage using MP2/6-31G calculation.32 They have shown that water clusters adopt structures significantly different from those in the gas phase. The hydrogen bonds are not intact in the endohedral complex due to the pressure effect introduced by the C60 cage. To study the spatial effect on the vibrational spectra, Sathyamurthy and co-workers have studied the HF, H2O, NH3, and CH4 inside fullerene.33 The vibrational modes of small molecules exhibit blue shift due to structural and electronic confinements.33 In this investigation, a systematic attempt has been made to probe the endohedral complexes of different anions such as F, Cl, and Br with C30, C32, C34, C36, C60, and C70 molecules using B3LYP method.41,42 In addition, the structure and stability of OH and CN inside the C60 and C70 have also been

ARTICLE

investigated. It can be seen that the model systems are useful to gain insight into the extent of spatial and electronic confinements on the anions. Thus, it is possible to address the effect of pressure exerted by different fullerenes on the anions upon endohedral complex formation. In addition, the dynamic behavior of the anion inside the cage has also been investigated using BOMD method.43,44

’ COMPUTATIONAL DETAILS The geometries of all the anion 3 3 3 fullerene complexes were initially optimized without any geometrical constrain using B3LYP/6-31G* model chemistry. The minimum energy nature of the geometries was characterized by frequency analysis at the same level of theory. The B3LYP/6-31G* optimized geometries were further optimized at B3LYP/6-311+G* level of theory without any geometrical constrain and the same geometries have been used for the further calculations throughout the text. The interaction energy (IE) was calculated using a supermolecule approach, applying the following equation: IE ¼ Etotal ðEfullerene þ Eanion Þ where Etotal is the total energy of the complex, Efullerene is the energy of the fullerene, and Eanion is the energy of the anion (i.e., F, Cl, Br, OH, and CN), respectively. The monomer energies were calculated from the respective monomer geometries in the complexes. The calculated IEs were corrected for the basis set superposition error (BSSE) using the counterpoise method suggested by Boys and Bernardi.45 Furthermore, the atom in molecule (AIM) approach was used for the characterization of the nature of the noncovalent interaction.46,47 The wave functions for all the anion 3 3 3 fullerene interaction systems were generated using HF/6-311+G* level of theory. The AIM calculations were carried out using AIM-2000 program.48 To understand the nature of stability of endohedral complexes, the energy decomposition analysis was carried out employing the Ziegler-Morokuma energy decomposition analysis scheme.4951 These calculations were performed using the B3LYP-D/TZP level of theory. The Amsterdam density

Figure 1. Optimized geometries of various anions in different confinements using a B3LYP/6-311+G* level of theory (gray = carbon, cyan = fluorine, green = chlorine, dark red = bromine). 11724

dx.doi.org/10.1021/jp203421v |J. Phys. Chem. A 2011, 115, 11723–11733

The Journal of Physical Chemistry A

ARTICLE

Figure 2. Optimized geometries of various anions in different confinements using B3LYP/6-311+G* level of theory.

functional (ADF) theory software package was used for the decomposition analysis.52 The BOMD simulations were performed on the anion fullerene complex. The Born-Openheimer potential energy surface was generated using Hessian-based integrator by the fifthorder polynomial and rational function fit utilizing predictorcorrector interpolation method. In the BOMD approach, the wave functions were converged to yield the more accurate potential energy surface for the dynamics calculations. The BO potential energy surface was generated using B3LYP/6-31G* and B3LYP/6-31+G* levels of theories. The simulations were carried out using 298 K temperature. The trajectories were collected for every ≈0.6 fs. All the calculations were performed using the Gaussian 03 suite of programs.53 The trajectories were used for the energy decomposition analysis at B3LYP/TZP level of theory to understand the various factors influencing the anion encapsulation and stabilization in the confinement.

’ RESULTS AND DISCUSSIONS Geometrical Parameters. As stated above, C30, C32, C34, C36, C60, and C70 molecules offer a different extent of spatial and electronic environment for encaging anions. In the remaining part of the text, C30, C32, C34, and C36 are referred to as smaller fullerenes. Both C60 and C70 are called larger fullerenes. The B3LYP/6-311+G* optimized geometries of all the monatomic anions encapsulated in smaller fullerenes are shown in Figure 1. The distance between the center of fullerene and anion is used as criteria to understand the effect of confinement. Furthermore, the closest distance between the anion and five-membered ring (six-membered ring) is also taken as additional criteria to probe

Table 1. Calculated Interaction Energies at B3LYP/6-311 +G* Level for Various Endohedral Complexesa interaction energy fullerenes

a

F

Cl

Br

C30

16.04

166.42

227.29

C32

6.040

154.37

219.47

C34 C36

14.87 27.87

118.30 85.75

175.30 139.35

C60

43.53

26.84

16.41

C70

40.11

30.19

23.62

All the energies are given here are in kcal/mol.

the effect of confinement. Examination of these parameters shows that anions encapsulated inside the smaller fullerenes are almost located at the center of the same. Therefore, the pressure exerted by the smaller fullerenes on the anions is symmetrical. The optimized geometries of the anions encapsulated inside the larger fullerene are given in Figure 2. The B3LYP/6-311+G* calculations yield the distances between center of C60 and F and Cl as 0.42 and 0.19 Å, respectively. On the other hand, the same distances in the case of anions encapsulated inside C70 are 1.46 and 0.24 Å, respectively. It can be seen that the F does not lie at the center of C70, whereas Cl is relatively closer to the center of the cage (C70). Examination of results for Br@C60 and Br@C70 reveals that Br is located at the center of fullerenes. It can be found that, in both the confinements, the F is closer to the center of the five-membered ring. In the case of F@C60, the calculated distance between the center of the 11725



ARTICLE

Figure 3. Molecular graphs of the various anions encapsulated inside C60 and C70.

nearest five-membered ring and F is 2.90 Å. The distance between center of all the other nearer six-membered rings and F is ∼2.93 Å. In the case of F@C70, the distance from the center of the five-membered ring and F as well as the center of the sixmembered ring and F are 2.50 and 2.63 Å, respectively. The calculated geometrical parameters of encapsulated Cl in C60 and C70 show the higher preference of Cl for the six-membered ring than the five-membered ring. Interaction Energies. The calculated IEs of all the complexes are listed in Table 1. The calculated IEs for F, Cl, and Br encapsulated in C30 are 16.04, 166.42, and 227.29 kcal/mol, respectively. It can be seen that the anions are not stable inside C30 due to the dominant repulsive interaction between the anions and fullerene. C32 is the smallest fullerene that can encage F. It can be seen from the IEs that none of the smaller fullerenes considered in this study can accommodate Cl and Br. The stabilization of all these incarcerated anions in C60 and C70 is evident from the IE values. The calculated IEs for F@C60, Cl@C60, and Br@C60 are 43.53, 26.84, and 16.41 kcal/mol, respectively. The decrease in the IEs with an increase in the size of the anions is evident from these values. Geerlings and co-workers have reported the IEs for F@C60, Cl@C60, and Br@C60 as 24.54, 5.29, and 7.73 kcal/mol, respectively.31 It can be noted from their results that Br is not stable inside the C60 cage. In addition, it can be noted that the magnitude of the IEs for F@C60 and Cl@C60 are also significantly less than that of present values. The discrepancy in the values is due to the level of calculation and quality of basis set. The IEs of the same anions inside the C70 cage are 40.11, 30.19, and 23.62 kcal/mol, respectively.

Table 2. Energy Decomposition Analysis Using B3LYP-D/ TZP Level of Theory Employing Ziegler-Morokuma Schemea fullerene anion C30

F

VPauli 232.10

Cl 778.31 C32

C34

C36

C60

C70

a

Eelec

Esteric

160.11 71.99

Eorbital

Edispersion

62.86

6.00

IE 3.14

438.81 339.50 180.76 2.81

155.93

Br 1087.32 609.21 478.11 253.65 2.65

221.83

F 170.45 Cl 589.11

132.13 38.31 50.96 349.32 239.79 90.73

20.46 145.48

Br 873.03

509.90 363.12 146.58 3.42

213.15

F

120.36 26.03

7.82 3.59

47.57

9.73

31.27

Cl 511.54

311.32 200.23 86.44

5.25

108.55

Br 759.16

454.35 304.82 131.72 4.93

168.18

F

101.97 7.15

146.39

109.12

41.47

11.99 46.32

Cl 445.56

277.95 167.61 71.38

7.34

88.90

Br 622.70 F 13.75

387.19 235.51 97.94 43.87 30.12 20.32

6.34 9.26

131.23 59.70

Cl 58.06

68.65

10.59 16.31

21.42 48.33

Br 99.75

97.02

2.73

16.74

31.62 45.62

F

28.31

49.90

21.59 25.48

9.57

Cl 33.42

52.98

19.55 12.67

17.30 49.53

Br 60.70

71.61

10.92 12.23

26.15 49.30

56.64


The present study confirms that Br is stable inside the C60 and C70 cages in contrast to the previous report.31 AIM Analysis. Calculated AIM molecular graphs for the various endohedral complexes are shown in Figure 3. The calculated 11726



ARTICLE

Table 3. Calculated HOMO-LUMO Energies of Various Systemsa F

isolated fullerene ELUMO

EHOMO 0.08715

0.01291

0.08416

0.01121

0.07602

0.01408

C32

0.24586

0.15043

0.10456

0.00802

0.07147

0.01521

0.07139

0.01722

C34

0.21340

0.16044

0.07341

0.0211

0.07645

0.02451

0.07765

0.02508

C36

0.20166

0.15165

0.06659

0.01645

0.07456

0.02272

0.07905

0.02498

C60

0.23705

0.13702

0.10504

0.02261

0.11424

0.02329

0.10579

0.02425

C70

0.23478

0.13659

0.10878

0.02963

0.11262

0.02952

0.10619

0.03019

0.01292

0.40652

0.02736

0.22796

0.03077

0.18136

C30

isolated anions

ELUMO

EHOMO

Br

EHOMO

fullerene

a

Cl ELUMO

EHOMO

ELUMO

All the energies are given here are in a.u.

Figure 4. Optimized geometries of various anions in different confinements using B3LYP/6-311+G* level of theory.

electron density (F(rc)) and its Laplacian (r2F(rc)) at bond critical points (BCPs) are given in Supporting Information (Tables S1S3). These values are closer to the standard values stipulated for these kinds of interactions. The molecular graphs and the presence of BCPs indicate the favorable interaction of F with the five-membered ring of C60. In both F@C60 and F@C70 complexes, five BCPs have been observed, indicating the favorable interaction between the anion and the five-membered rings. The other four complexes show a large number of BCPs between anions and cages. It is interesting to note that the molecular graph of Br@C60 exhibits 60 BCPs, implying Br interacts with all the carbon atoms of the C60. Energy Decomposition Analysis. Various components of interaction energy, Pauli repulsion (VPauli), electrostatic interaction (Eelec), steric interaction (Esteric = VPauli + Eelec), orbital interaction (Eorbital), and dispersion interaction (Edispersion), along with IE (Esteric + Eorbital + Edispersion), obtained from

Morokuma and Ziegler decomposition analysis of all the endohedral complexes using B3LYP-D/TZP method, are presented in Table 2. It can be seen that the trend in the IEs calculated using the above-mentioned scheme is akin to that of B3LYP/6-311+G* level of calculation. Close analysis of the IE components clearly reveals that the steric term dominants the overall energy in the case of anions encapsulated inside the smaller fullerenes. It can be noted that with an increase in the size of the anion there is a significant increase in the steric energy. The significant repulsion between the cages and the anions is responsible for the instability of the anions inside the C30 cage. As expected, the steric energy decreases with increase in the size of the fullerenes (C32 onward). It can be noted that for other systems (C32C36), there is a significant decrease in ESteric and increase in EOrbital contributions which reveals the concomitant stability of the fullerene and anion complexes. The contribution from dispersion interaction to the 11727



ARTICLE

IE in the case of smaller fullerenes with F increases with the increase in the size of fullerene. The importance of various contributions in the stabilization of anions inside larger fullerenes is evident from the results displayed in Table 2. The steric energy contribution for F@C60 and F@C70 are 30.12 and 21.59 kcal/mol. The same contribution for Br@C60 and Br@C70 are 2.73 and 10.92 kcal/mol. Therefore, stabilization of Br inside the C60 arises due to orbital interaction. Thus, evidence shows that the intricate balance between the size and electronic effect arises due to confinement, which is necessary for the stabilization of the anions inside the cages. The variations in the dispersion contribution to the IE of larger fullerenes with encapsulated F are only marginal. Typically, the calculated Edispersion for F@C60 and F@C70 are 9.26 and 9.57 kcal/mol, respectively. However, the changes in the same contribution to the IE of smaller fullerene with F and larger fullerenes with anions such as Br are significant. HOMO and LUMO Energies of the Complexes. HOMO and LUMO energies of various isolated fullerenes, isolated anions, and encapsulated complexes are listed in Table 3. Results reveal that orbitals of anions and fullerenes undergo significant changes Table 4. Calculated Geometrical Parameters, Stretching Frequencies, and Energetics of Endohedral Complexesa geometry (Å)

a

IR frequency (cm1) νOH

νCN

IE (kcal/mol) OH@ CN@

system

OH

CN

isolated

0.97

1.18

3416.48 (0) 2139.35 (0)

C60

0.97

1.17

3772.48 (2) 2236.31 (2) 35.21 19.39

C70

0.97

1.18

3768.87 (2) 2162.62 (0) 35.35 29.08

The numbers in the parentheses indicates the number of imaginary frequencies.

upon encapsulation. The degeneracy of the valence orbital of all monatomic anions is 3-fold. The valence orbitals of C60 and C70 are 5-fold and 3-fold degenerate.31 The anion encapsulation removes the degeneracy of the valence orbitals of fullerenes. In all the cases, the HOMO of the complexes has the maximum character of the anion. The HOMO-1 orbital of complexes exhibits the character of the fullerenes. Moreover, it is noteworthy to mention that the energies of the orbitals of anion are numerically higher than those of complexes while the orbitals of the fullerene are numerically lower when compared with the valence orbitals of complexes. These findings clearly emphasize the stabilization of frontier orbitals of anions in the confinement. Encapsulation of Diatomic Anions in Fullerenes. B3LYP/ 6-311+G* level optimized geometries of OH and CN diatomic anions encapsulated inside C60 and C70 are shown in Figure 4 along with the important geometrical parameters. In the case of OH @C 60 , OH does not coincide with the center of the C60. Typically, the calculated distances for OH@C60 and OH@C70 are 0.68 and 1.11 Å, respectively. The corresponding values in the case of CN encapsulation are 0.08 and 0.19 Å, respectively. The geometrical parameters of the anion in various environments, the anionic stretching frequencies, and IEs are given in Table 4. The interatomic distance between O and H as well as C and N does not undergo significant changes upon encapsulation. The calculated IR stretching frequencies of the isolated OH and CN significantly different from that obtained in the confined environment. The isolated stretching frequencies for these anions are 3416.48 and 2139.35 cm1, respectively. Both OH and CN stretching frequencies undergo blue shift upon formation endohedral complexes. The blue shift of OH group in OH@C60 and OH@C70 complexes are 356 and 352 cm1, respectively. The same for the CN group in CN@C60 and

Figure 5. Molecular graphs of the various diatomic anions encapsulated inside C60 and C70. 11728



ARTICLE

Table 5. Calculated Electron Density and its Laplacian at the Bond Critical Point of Anions (All the Quantities are in a.u.) isolated anion

F(rc)

r F(rc)

OH

0.36166

CN

0.49208

a

in C60

in C70

F(rc)

r F(rc)

F(rc)

0.50724

0.35335

0.47864

0.35442

0.48624

0.07766

0.47598

0.12272

0.46520

0.12628

2

b

a

2

b

r2F(rc)b

a

Table 6. Energy Decomposition Analysis of Endohedral Complexes Containing Diatomic Anionsa fullerene anion VPauli C60 C70 a

Eorbital

Edispersion

IE

OH

29.27 51.61 22.34 19.91

13.96

56.20

CN

74.00 76.99 3.00

18.76

25.35

47.11

21.11 45.26 24.16 18.11 35.10 54.52 19.42 13.12

12.23 20.49

54.49 53.03

OH CN

Eelec

Esteric

Figure 6. Calculated BO potential energy surface at B3LYP/631G* level.


CN@C70 are 96.96 and 23.27 cm1, respectively. Although there are no significant changes in the interatomic distances, both OH and CN exhibit blue shifts inside the fullerenes. Similar findings have also been reported by Sathyamurthy and co-workers.33 They have reported that the bond with the lower force constant is affected more by the confinement.33 It is known that force constant for OH is less than that of CN. Thus, the OH group undergoes considerable blue shift upon encapsulation when compared to the CN group. Similarly, Cioslowski had already shown that the stretching frequencies of H2, N2, CO, and LiH encapsulated inside the fullerene exhibit blue shift.27 Charkin et al. have also reported similar observations in the stretching frequencies of MX4 type molecules inside cage molecules.54 Based on these findings, it is possible to conclude that the origin of blue shift in the stretching frequencies of OH and CN groups is due to the geometrical confinement or chemical pressure exerted by the fullerenes. The calculated IE values reveal the feasibility of formation of these complexes. The calculated values show that OH can be accommodated well inside the fullerenes. The change in the confinement (C70) has marginal effect on its IE. On the other hand, the endohedral complex formation CN exhibits size effect. Both sizes of the anions and confinement play roles in the formation of complexes. It can be seen that the difference in the IEs of CN@C60 and CN@C70 is 9.69 kcal/mol. The AIM molecular graphs of OH and CN encapsulated C60 and C70 are presented in Figure 5. The calculated F(rc) and r2F(rc) values for the various CPs are given in Supporting Information. Existence of BCPs between cages and anions and the calculated F(rc) and r2F(rc) values clearly reveals the nature of weak interaction between the two systems. Further, to gain insight in to the electronic/structural pressure effect, the F(rc) and r2F(rc) values at the BCP of the anion were obtained from the AIM calculations and the results are presented in Table 5. It can be found that the charge density at the BCP decreases due to electronic and structural confinement. In the neighborhood of the anion in the confined state, there are number of number of (3,+3) CPs with significant electron density values. Overall, the geometry, IR spectral information, and AIM analysis succinctly provide insight into the effect of confinement. Various components of IE are given in Table 6. It can be noticed from the table

Figure 7. Variation of geometrical parameters (the distance between the F and Cn (n = 130)) with time.

Figure 8. Snapshots of F@C30 obtained from BOMD simulation at B3LYP/6-31G* level.

that the dispersion contribution to the IEs of OH @C 60 and CN@C60 complexes are 24.83 and 53.81%, respectively. 11729


The Journal of Physical Chemistry A The same values calculated for the OH@C70 and CN@C70 complexes are 22.44 and 38.63%, respectively. The changes in the Edispersion contribution from C60 to C70 may be attributed due to the differences in the confinement. BOMD of F@C30. It can be noted from the IE of F@C30 that F is not stable inside the C30. Therefore, F may leave the cage by causing structural distortion to the same. With a view to gain insight into the escaping tendency of F in the confined environment, BOMD simulation was carried out on F@C30 complex for 100 fs. The BO potential energy surface was generated using B3LYP/6-31G* level of theory. The calculated BO potential energy surface is displayed in Figure 6. It is reported that diffuse functions are important for systems where electrons are far away from the nucleus, such as: molecules with lone pairs, anions, and other systems with significant negative charges.55

ARTICLE

Thus the BO potential energy surface of F@C30 was also generated using B3LYP method with 6-31+G* basis set. The variation in the distance between the F and Cn (n = 130) is shown in Figure 7. It can be seen from the variation in the geometrical parameters that the anion marginally fluctuates about/around the center of the cage. However, F ion does not leave the cage. To understand further, the snapshots of F@C30 complexes were obtained from the BOMD simulation. The different snapshots are displayed in Figure 8. The IEs and their components were calculated for all the snapshots obtained from the trajectories generated using B3LYP method employing 6-31G* and 6-31+G* basis sets. The variation of IE with time along with its components is depicted in Figure 9. Results obtained from the B3LYP/6-31G* and B3LP/ 6-31+G* levels are denoted as A and B, respectively, in Figure 9.

Figure 9. Variation of interaction energy of the complexes along with its components with time: (A) trajectories generated using B3LYP/6-31G* level and (B) trajectories generated using B3LYP/6-31+G* level. 11730



ARTICLE

Figure 10. Variation of calculated electron localization function (ELF) of F@C30 with time (isosurface value = 0.09).

geometries of the C30 significantly influence the motion of anion. However, the anion is unable to cross the structural confinement. Furthermore, the ELFs clearly reveal marginal changes in the electron localization function during time evolution and hence electronic structure of the anion. The IE component analysis clearly provides the changes in the different components with time evolution. The calculated HOMOLUMO energies of various trajectories obtained on the BO potential energy surface are depicted in Figure 11. It can be seen from the frontier orbital energies the difference of these ranges from 1.453 to 1.986 eV.

Figure 11. Variation of HOMOLUMO energy with time.

The calculated IE value using the B3LYP/6-31G* method ranges from 4.19 to 11.28 kcal/mol, whereas the same calculated using B3LYP/6-31+G* varies from 3.32 to 9.55 kcal/mol. The comparison of results shows that the incorporation of diffuse functions is necessary for the generation of BO surface because the B3LYP/6-31G* level predicts an IE of 4.19 kcal/mol, which is in contrast to the static calculation at the B3LYP/6-311+G* level and energy decomposition analysis using the B3LYP-D/TZP method. These findings clearly reveal that F is energetically and thermodynamically unstable inside C30. The calculated electron localization function (ELF) for various snapshots is shown in Figure 10. It can be noticed that the

’ CONCLUSIONS Present study clearly highlights the encapsulation of mono and diatomic anions in the inner space of the fullerenes. In contrast to the previous report that Br is stable inside the C60. The discrepancy in the findings mainly arises from the level of calculation and the quality of the basis set. The IEs of incarcerated anions clearly reveal the effect of electronic/structural pressure on the anions. As explained in the number of previous studies, the sizes of the anions and fullerenes determine the stability of the anions inside the cage. The stretching frequencies of diatomic anions exhibit blue shift due to the pressure effect of cage. The theory of AIM indicates the existence of noncovalent interactions between cage and anions. Although, the encapsulation of F is not energetically favorable inside the C30, the BOMD results do not exhibit any escaping tendency of anion from the cage. Furthermore, evidence from the BOMD illustrate that F oscillates around the center of the cage leading to significant geometrical distortion in the cage. 11731



’ ASSOCIATED CONTENT

bS

Supporting Information. AIM data of the larger fullerene with anion. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*Tel.: +91 44 24411630. Fax: +91 44 24911589. E-mail: [email protected], [email protected].

’ ACKNOWLEDGMENT We thank the Center of Excellence for Computational Chemistry (Project No. NWP-53), Council of Scientific and Industrial Research (CSIR), New Delhi, for financial support. One of the authors (P.R.) wishes to thank CSIR, New Delhi, India, for the award of Senior Research Fellowship. ’ REFERENCES (1) Kroto, H. W.; Heath, J. R.; Obrien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162–163. (2) Hirsch, A. The Chemistry of the Fullerenes; Thieme: Stuttgart, 1994. (3) The Chemistry of Fullerenes; Taylor, R., Ed., World Scientific: Singapore, 1995. (4) Dresselhaus, M. S.; Dresselhaus, G.; Eklund, P. C. Science of Fullerenes and Carbon Nanotubes; Academic Press: San Diego, CA, 1996. (5) Kadish, K. M.; Ruoff, R. S. Fullerenes; Wiley: New York, 2000. (6) Heath, J. R.; OBrien, S. C.; Zhang, Q.; Liu, Y.; Curl, R. F.; Kroto, H. W.; Tittel, F. K.; Smalley, R. E. J. Am. Chem. Soc. 1985, 107, 7779–7780. (7) Chai, Y.; Guo, T.; Jin, C.; Haufler, R. E.; Chibante, L. P. F.; Fure, J.; Wang, L.; Alford, J. M.; Smalley, R. E. J. Phys. Chem. 1991, 95, 7564–7568. (8) Weiske, T .; Bohme, D. K.; Hrusak, J.; Kratschmer, W.; Schwarz, H. Angew. Chem., Int. Ed. 1991, 30, 884–886. (9) Takata, M.; Umeda, B.; Nishibori, E.; Sakata, M.; Saitot, Y.; Ohno, M.; Shinohara, H. Nature 1995, 377, 46–49. (10) Endofullerenes: A New Family of Carbon Cluster; Akasaka, T., Nagase, S., Eds.; Kluwer: Dordrecht, 2002. (11) Liu, S.; Sun, S. J. Organomet. Chem. 2000, 599, 74–86. (12) Guha, S.; Nakamoto, K. Coord. Chem. Rev. 2005, 249, 1111– 1132. (13) Murata, M.; Murata, Y.; Komatsu, K. Chem. Commun. 2008, 6083–6094. (14) Chaur, M. N.; Melin, F.; Ortiz, A. L.; Echegoyen, L. Angew. Chem., Int. Ed. 2009, 48, 7514–7538. (15) Yamada, M.; Akasaka, T.; Nagase, S. Acc. Chem. Res. 2010, 43, 92–102. (16) Kruse, H.; Grimme, S. J. Phys. Chem. C 2009, 113, 17006– 17010. (17) Korona, T.; Hesselmann, A.; Dodziuk, H. J. Chem. Theory Comput. 2009, 5, 1585–1596. (18) Pinzon, J. R.; PlonskaBrzezinska, M. E.; Cardona, C. M.; Athans, A. J.; Gayathri, S. S.; Guldi, D. M.; Herranz, M. A.; Martin, N.; Torres, T.; Echegoyen, L. Angew. Chem., Int. Ed. 2008, 47, 4173–4176. (19) Heflin, J. R.; Marciu, D.; Figura, C.; Wang, S.; Burbank, P.; Stevenson, S.; Dorn, H. C. Appl. Phys. Lett. 1998, 72, 2788–2790. (20) Shinohara, H. Rep. Prog. Phys. 2000, 63, 843. (21) Mikawa, M.; Kato, H.; Okumura, M.; Narazaki, M.; Kanazawa, Y.; Miwa, N.; Shinohara, H. Bioconjugate Chem. 2001, 12, 510–514. (22) Sitharaman, B.; Wilson, L. J. J. Biomed. Nanotechnol. 2007, 3, 342–352.

ARTICLE

(23) Vougioukalakis, G. C.; Roubelakis, M. M.; Orfanopoulos, M. Chem. Soc. Rev. 2010, 39, 817–844. (24) Wolfrum, S.; Pinzon, J. R.; MolinaOntoria, A.; Gouloumis, A.; Martín, N.; Echegoyen, L.; Guldi, D. M. Chem. Commun 2011, 47, 2270–2272. (25) Chaur, M. N.; Melin, F.; Ortiz, A. L.; Echegoyen, L. Angew. Chem., Int. Ed. 2009, 48, 7514–7538. (26) Osuna, S.; Swart, M.; Sola, M. Phys. Chem. Chem. Phys. 2011, 13, 3585–3603. (27) Cioslowski, J.; Fleischmann, E. D. J. Chem. Phys. 1991, 94, 3730–3734. (28) Cioslowski, J. J. Am. Chem. Soc. 1991, 113, 4139–4141. (29) Cioslowski, J.; Nanayakkara, A. J. Chem. Phys. 1992, 96, 8354–8362. (30) Cioslowski, J.; Raghavachari, K. J. Chem. Phys. 1993, 98, 8734– 8741. (31) (a) De Proft, F.; Alsenoy, C. V.; Geerlings, P. J. Phys. Chem. 1996, 100, 7440–7448. (b) Borgoo, A.; Tozer, D. J.; Geerlings, P.; De Proft, F. Phys. Chem. Chem. Phys. 2008, 10, 1404–1410. (32) Ramachandran, C. N.; Sathyamurthy, N. Chem. Phys. Lett. 2005, 410, 348–351. (33) Shameema, O.; Ramachandran, C. N.; Sathyamurthy, N. J. Phys. Chem. A 2006, 110, 2–4. (34) Harneit, W. Phys. Rev. A 2002, 65, 032322–032324. (35) Valencia, R.; RodrıguezFortea, A.; Clotet, A.; de Graaf, C.; Chaur, M. N.; Echegoyen, L.; Poblet, J. M. Chem.Eur. J. 2009, 15, 10997–11009. (36) Kobayashi, K.; Nagase, S.; Yoshida, M.; Osawa, E. J. Am. Chem. Soc. 1997, 119, 12693–12694. (37) Popov, A. A.; Dunsch, L. J. Am. Chem. Soc. 2007, 129, 11835– 11849. (38) Popov, A. A.; Dunsch, L. Chem.Eur. J. 2009, 15, 9707–9729. (39) Wu, X.; Lu, X J. Am. Chem. Soc. 2007, 129, 2171–2177. (40) Jemmis, E. D.; Subramanian, G.; Sastry, G. N.; Mehta, G.; Shirsat, R. N.; Gadre, S. R. J. Chem. Soc., Perkin Trans. 2 1996, 2343–2346. (41) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (42) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785–789. (43) Millam, J. M.; Bakken, V.; Chen, W.; Hase, W. L.; Schlegel, H. B. J. Chem. Phys. 1999, 111, 3800–3805. (44) Li, X.; Millam, J. M.; Schlegel, H. B. J. Chem. Phys. 2000, 113, 10062–10067. (45) Boys, S. F.; Bernardi, F. Mol. Phys. 1970, 19, 553–566. (46) Bader, R. F. W. Atoms in Molecules: A Quantum Theory; Clarendon Press: Oxford, United Kingdom, 1990. (47) Popelier, P. L. A. Atoms in Molecules: An Introduction; Prentice Hall: New York, 2000. (48) BieglerKonig, F.; Schonbohm, J.; Derdav, R.; Bayles, D.; Bader, R. F. W. AIM2000, version 1; Bielefeld, Germany, 2000. (49) Morokuma, K.; Kitaura, K. Energy decomposition analysis of molecular iteractions. In Chemical Applications of Atomic and Molecular Electrostatic Potentials; Politzer, P., Truhlar, D. G., Eds.; Plenum: New York, 1981. (50) (a) Ziegler, T.; Rauk, A. Theor. Chim. Acta 1977, 46, 1–10. (b) Ziegler, T.; Rauk, A. Inorg. Chem. 1979, 18, 1558–1565. (51) Bickelhaupt, F. M.; Baerends, E. J. In Reviews in Computational Chemistry; Wiley: New York, 2000; Vol. 15. (52) Amsterdam Density Functional (ADF) version 2009.01. http://www.scm.com. (53) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; 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.; Ayala, P. Y.; 11732



ARTICLE

Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; lifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; AlLaham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision E.01; Gaussian, Inc.: Wallingford, CT, 2004. (54) Charkin, O. P.; Klimenko, N. M.; Charkin, D. O.; Mebel, A. M. Russ. J. Inorg. Chem. 2004, 49, 723–733. (55) Foresman, J. B.; Frisch, A. E. Exploring Chemistry with Electronic Structure Methods: A Guide to Using Gaussian, 2nd ed.; Gaussian, Inc.: Pittsburgh, PA, 1996; pp 97110.

11733


Studies on the Encapsulation of Various Anions in Different Fullerenes

Recommend Documents