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Endohedral complexes of C58 cage with H2 and CO
Chemical Physics Letters 390 (2004) 472–474 www.elsevier.com/locate/cplett
Endohedral complexes of C58 cage with H2 and CO Yun Hang Hu *, Eli Ruckenstein Department of Chemical and Biological Engineering, State University of New York at Buffalo, 303 Furnas Hall Amherst, Buffalo, NY 14260, USA Received 2 February 2004; in final form 15 April 2004 Available online 6 May 2004
Abstract Ab initio Hartree–Fock (HF) calculations were carried out to determine the structures and energies of the endohedral complexes of C58 cage with H2 or CO. It was demonstrated that the formation of these complexes is endothermic with destabilization energies of 3.3 kcal/mol for H2 and 18.6 kcal/mol for CO. Furthermore, the H2 and CO molecules have different orientations in the C58 cage, namely, the orientation of the molecular axis of the former is normal to the face of the 7-member ring, while that of the latter is parallel to that face. In addition, the H–H bond of the H2 molecule is shortened inside the cage, whereas the length of the C–O bond remains unchanged. Ó 2004 Elsevier B.V. All rights reserved.
The fullerene cages, which were discovered in 1985 [1], and the related nano-tubes constitute ideal building blocks for a carbon-based nanotechnology. The most prominent representative of the fullerenes is C60 , which is the most abundant cluster in the solvent-extracted carbon soot and the smallest fullerene that satisfies the isolated pentagon rule. One of the fascinating properties of the fullerenes is their ability to trap atoms and small molecules inside their cages. The first evidence for endohedral complexes was reported soon after the discovery of C60 in 1985 [2], and has attracted special attention from theoretical [3–7] and experimental points of view [8–11]. Cioslowski et al. [6,12,13] investigated theoretically the problem of the stability of C60 containing some atoms, ions, or small molecules inside its cage. They found that C60 can destabilize the non-polar (or weakly polar) molecules, such as H2 and CO, trapped inside its cage [6]. The destabilization energies of CO and H2 were 11.2 and 1.2 kcal/mol, respectively [6]. These results indicate that the formation of the endohedral complexes, consisting of H2 (or CO) and C60 , is an endothermic process. In this Letter, we will investigate the endohedral complexes of C58 with H2 or CO using the ab initio Hartree–Fock (HF) method. Because *
Corresponding author. Fax: 716-645-3822. E-mail address: yhu@buffalo.edu (Y.H. Hu).
0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.04.060
the C58 cage, which contains a 7-member ring besides the 5- and 6-member rings, differs from C60 , which consists of only 5- and 6-member rings, this letter will reveal how a 7-member ring affects the structures and energies of endohedral complexes. The structure of C60 , which possesses twelve 5-member rings and twenty 6-member rings, was examined both theoretically [14–17] and experimentally [18,19]. Based on a balance between the calculation accuracy and the cost, the HF and the density functional theory (DFT) methods became the most popular ab initio procedures for the fullerene system. Although the B3LYP hybrid DFT [20], which was widely employed in various calculations [21–23], can provide satisfactory predictions for the perfect and defect C60 cages even with a small basis orbital set (such as 3-21G) [24,25], the HF method may constitute a better choice to deal with the interaction between a host molecule and the fullerene cage. This happens because the electronic structures of the endohedral complexes of C60 cage with some host molecules can be best described as resulting from the interaction between a polarizable double-layer C60 cage and the electrostatic potential generated by the guest [6,13]. The exact exchange energy, which is fully taken into account by the HF method, is important for such electrostatic interactions, whereas the contribution of the electron correlation is minor. Therefore, in this
Y.H. Hu, E. Ruckenstein / Chemical Physics Letters 390 (2004) 472–474
Letter, the HF method with the relatively small basis orbital set 3-21G and the large orbital basis set 6-311G(d) was selected for the geometry optimization and energy calculations, respectively. Furthermore, because incomplete basis sets were employed in these calculations, the Boys–Bernardi counterpoise procedure was applied for the basis set superposition error (BSSE) correction [26]. The calculations have been carried out using the GA U S S I A N 94 program [27]. The C58 was detected by mass spectrometry [28], and its formation during the fragmentation of C60 was investigated theoretically [29]. Furthermore, theoretical calculations predicted that the most stable structure of C58 was generated by removing two neighboring atoms from the C60 cage. It consisted of a 7-member ring with thirteen 5- and seventeen 6-member rings [24]. Therefore, this most stable C58 structure was employed for the endohedral complex calculations. As shown in Figs. 1a and b, H2 and CO are located in central positions inside the C60 cage. Furthermore, the energy calculations showed that both H2 and CO were destabilized inside the C60 cage, with destabilization energies of 2.3 kcal/mol for H2 and 16.4 kcal/mol for CO (Table 1). These results are consistent with the HF calculations of Cioslowski [6]. As the C60 cage, C58 cage also destabilized H2 and CO inside its cage with destabilization energy of 3.3 kcal/mol for H2 and 18.6 kcal/ mol for CO. These results indicate that the C60 and C58 cages exhibited similar performances in the formation of endohedral complexes with H2 or CO, the formation of endohedral complexes between the cage and H2 (or CO)
Fig. 1. Endohedral Complexes of C60 with (a) H2 and (b) CO.
Table 1 Destabilization energies and bond lengths of H2 and CO in C60 and C58 cages Endohedral complex
Stabilizationa (kcal/mol)
H–H bond length A
C–O bond length A
H2 H2@C60 H2@C58 CO CO@C60 CO@C58
– 2.3 3.3 – 16.4 18.6
0.7348 0.7357 0.7339 – – –
– – – 1.1289 1.1281 1.1288
a Destabilization energy ¼ endohedral complex energy ) (guest molecule energy + fullerene cluster energy).
473
being in both cases endothermic. Although the endohedral complex of C60 with the H2 molecule was successfully synthesized using chemical ‘surgery’ methods [9,10], the preparation of endohedral complexes of C58 with H2 or CO constitutes still a challenge because macroscopic amounts of C58 are not yet available. However, Christian et al. [30] identified the formation of a C59 O cluster during the collision reaction of Oþ with C60 at an energy of 13 eV. They suggested that an endohedral complex of C58 with CO might constitute a possible form for the cluster. The H2 and CO molecules trapped inside the C58 cage have different orientations. As shown in Figs. 2a and b, the H2 molecular axis is normal to the face of the 7member ring, whereas the CO molecular axis is parallel to that face. Two factors are responsible for the orientations of H2 and CO molecules: the polarity of the molecule and its size. If the polarity would constitute the main factor, the CO molecule, which is weakly-polar, should orient in the direction of the highest dipole moment of the cage. However, the calculations revealed that the CO molecule did not orient in the direction of the highest dipole moment of C58 . Therefore, the orientation of the non-polar or weakly-polar molecule is mainly dependent on the guest molecular size. Because the C–O bond is much longer than the H–H bond, the former is oriented parallel to the face of the 7-member ring (the cage being the longest in that direction), while the latter is oriented normal to the face of the 7-member ring. To further confirm this explanation, we considered that CO2 , which is non-polar and much longer than CO, was captured inside the C58 . The optimized structure did show that the CO2 molecule has the same orientation inside the cage as CO. In addition, the C60 and the C58 cages have different effects on the bond lengths of the guest molecules. The H–H bond of the guest hydrogen molecule was shortened inside the C58 cage, whereas the length of the C–O bond remained unchanged. In conclusion, the C60 and the C58 cages exhibit similar performances in the formation of endohedral complexes with H2 and CO, namely, the C58 cage destabilizes the guest molecule trapped inside. H2 and CO molecules have different orientations, the molecular axis orientation of the former being normal to the face of the 7-member ring, whereas that of the latter parallel.
Fig. 2. Endohedral complexes of C58 with (a) H2 and (b) CO.
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Y.H. Hu, E. Ruckenstein / Chemical Physics Letters 390 (2004) 472–474
Acknowledgements We are indebted to the reviewer for most helpful comments. References
[12] [13] [14] [15] [16] [17] [18]
[1] H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [2] J.R. Heath, S.C. O’Brien, Q. Zhang, Y. Liu, R.F. Curl, H.W. Kroto, F.K. Tittel, R.E. Smalley, J. Am. Chem. Soc. 107 (1985) 7779. [3] R.L. Murry, G.E. Scuseria, Science 263 (1994) 791. [4] M. Saunders, H.A. Jimenez-Vazquez, R.J. Cross, R.J. Poreda, Science 259 (1993) 1428. [5] S. Patchkovskii, W. Thiel, J. Am. Chem. Soc. 118 (1996) 7164. [6] J. Cioslowski, J. Am. Chem. Soc. 113 (1991) 4139. [7] M. B€ uhl, W. Thiel, H. Jiao, P. von Rague Schleyer, M. Saunders, F.A.L. Anet, J. Am. Chem. Soc. 116 (1994) 6005. [8] D.S. Bethune, R.D. Johnson, J.R. Salem, M.S. De Vries, Nature 366 (1993) 123. [9] Y. Rubin, T. Jarrosson, G. Wang, M.D. Bartberger, K.N. Houk, G. Schick, M. Saunders, R.J. Cross, Angew. Chem. Int. Ed. 40 (2001) 1543. [10] Y. Murata, M. Murata, K. Komatsu, J. Am. Chem. Soc. 125 (2003) 7152. [11] J.F. Nieregarten, Angew. Chem. Int. Ed. 40 (2001) 2973.
[19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
J. Cioslowski, E. Fleischmann, J. Chem. Phys. 94 (1991) 3730. J. Cioslowski, A. Nanayakkara, J. Chem. Phys. 96 (1992) 8354. M.D. Newton, R.E. Stanton, J. Am. Chem. Soc. 108 (1986) 2469. R.L. Disch, J.M. Schulman, Chem. Phys. Lett. 125 (1986) 465. B.I. Dunlap, D.W. Brenner, J.W. Mintmire, R.C. Mowrey, C.T. White, J. Phys. Chem. 95 (1991) 5763. M. H€aser, J. Alml€ of, G.E. Scuseria, Chem. Phys. Lett. 181 (1991) 497. J.M. Hawkins, A. Meyer, T.A. Lewis, S.D. Loren, F.J. Hollander, Science 252 (1991) 312. K. Hedberg, L. Hedberg, D.S. Bethune, C.A. Brown, H.C. Dorn, R.D. Johnson, M. de Vries, Science 254 (1991) 410. C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785. I.V. Alabugin, M. Manoharan, B. Breiner, F.D. Lewis, J. Am. Chem. Soc. 125 (2003) 9329. J.K. Wolken, F. Turecek, J. Phys. Chem. A 103 (1999) 6268. Y.H. Hu, J. Am. Chem. Soc. 125 (2003) 4388. Y.H. Hu, E. Ruckenstein, J. Chem. Phys. 119 (2003) 10073. Y.H. Hu, E. Ruckenstein, J. Chem. Phys. 120 (2004) 7971. S.B. Boys, F. Bernardi, J. Mol. Phys. 19 (1970) 553. M.J. Frisch et al., GA U S S I A N 94, Revision E.1, Gaussian Inc., Pittsburgh, PA, 1995. S.C. Obrien, J.R. Heath, R.F. Curl, R.E. Smalley, J. Chem. Phys. 88 (1988) 220. R.L. Murry, D.L. Strout, G.L. Odom, G.E. Scuseria, Nature 366 (1993) 665. J.F. Christian, Z. Wan, S.L. Anderson, Chem. Phys. Lett. 199 (1992) 373.
Endohedral complexes of C58 cage with H2 and CO Yun Hang Hu *, Eli Ruckenstein Department of Chemical and Biological Engineering, State University of New York at Buffalo, 303 Furnas Hall Amherst, Buffalo, NY 14260, USA Received 2 February 2004; in final form 15 April 2004 Available online 6 May 2004
Abstract Ab initio Hartree–Fock (HF) calculations were carried out to determine the structures and energies of the endohedral complexes of C58 cage with H2 or CO. It was demonstrated that the formation of these complexes is endothermic with destabilization energies of 3.3 kcal/mol for H2 and 18.6 kcal/mol for CO. Furthermore, the H2 and CO molecules have different orientations in the C58 cage, namely, the orientation of the molecular axis of the former is normal to the face of the 7-member ring, while that of the latter is parallel to that face. In addition, the H–H bond of the H2 molecule is shortened inside the cage, whereas the length of the C–O bond remains unchanged. Ó 2004 Elsevier B.V. All rights reserved.
The fullerene cages, which were discovered in 1985 [1], and the related nano-tubes constitute ideal building blocks for a carbon-based nanotechnology. The most prominent representative of the fullerenes is C60 , which is the most abundant cluster in the solvent-extracted carbon soot and the smallest fullerene that satisfies the isolated pentagon rule. One of the fascinating properties of the fullerenes is their ability to trap atoms and small molecules inside their cages. The first evidence for endohedral complexes was reported soon after the discovery of C60 in 1985 [2], and has attracted special attention from theoretical [3–7] and experimental points of view [8–11]. Cioslowski et al. [6,12,13] investigated theoretically the problem of the stability of C60 containing some atoms, ions, or small molecules inside its cage. They found that C60 can destabilize the non-polar (or weakly polar) molecules, such as H2 and CO, trapped inside its cage [6]. The destabilization energies of CO and H2 were 11.2 and 1.2 kcal/mol, respectively [6]. These results indicate that the formation of the endohedral complexes, consisting of H2 (or CO) and C60 , is an endothermic process. In this Letter, we will investigate the endohedral complexes of C58 with H2 or CO using the ab initio Hartree–Fock (HF) method. Because *
Corresponding author. Fax: 716-645-3822. E-mail address: yhu@buffalo.edu (Y.H. Hu).
0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.04.060
the C58 cage, which contains a 7-member ring besides the 5- and 6-member rings, differs from C60 , which consists of only 5- and 6-member rings, this letter will reveal how a 7-member ring affects the structures and energies of endohedral complexes. The structure of C60 , which possesses twelve 5-member rings and twenty 6-member rings, was examined both theoretically [14–17] and experimentally [18,19]. Based on a balance between the calculation accuracy and the cost, the HF and the density functional theory (DFT) methods became the most popular ab initio procedures for the fullerene system. Although the B3LYP hybrid DFT [20], which was widely employed in various calculations [21–23], can provide satisfactory predictions for the perfect and defect C60 cages even with a small basis orbital set (such as 3-21G) [24,25], the HF method may constitute a better choice to deal with the interaction between a host molecule and the fullerene cage. This happens because the electronic structures of the endohedral complexes of C60 cage with some host molecules can be best described as resulting from the interaction between a polarizable double-layer C60 cage and the electrostatic potential generated by the guest [6,13]. The exact exchange energy, which is fully taken into account by the HF method, is important for such electrostatic interactions, whereas the contribution of the electron correlation is minor. Therefore, in this
Y.H. Hu, E. Ruckenstein / Chemical Physics Letters 390 (2004) 472–474
Letter, the HF method with the relatively small basis orbital set 3-21G and the large orbital basis set 6-311G(d) was selected for the geometry optimization and energy calculations, respectively. Furthermore, because incomplete basis sets were employed in these calculations, the Boys–Bernardi counterpoise procedure was applied for the basis set superposition error (BSSE) correction [26]. The calculations have been carried out using the GA U S S I A N 94 program [27]. The C58 was detected by mass spectrometry [28], and its formation during the fragmentation of C60 was investigated theoretically [29]. Furthermore, theoretical calculations predicted that the most stable structure of C58 was generated by removing two neighboring atoms from the C60 cage. It consisted of a 7-member ring with thirteen 5- and seventeen 6-member rings [24]. Therefore, this most stable C58 structure was employed for the endohedral complex calculations. As shown in Figs. 1a and b, H2 and CO are located in central positions inside the C60 cage. Furthermore, the energy calculations showed that both H2 and CO were destabilized inside the C60 cage, with destabilization energies of 2.3 kcal/mol for H2 and 16.4 kcal/mol for CO (Table 1). These results are consistent with the HF calculations of Cioslowski [6]. As the C60 cage, C58 cage also destabilized H2 and CO inside its cage with destabilization energy of 3.3 kcal/mol for H2 and 18.6 kcal/ mol for CO. These results indicate that the C60 and C58 cages exhibited similar performances in the formation of endohedral complexes with H2 or CO, the formation of endohedral complexes between the cage and H2 (or CO)
Fig. 1. Endohedral Complexes of C60 with (a) H2 and (b) CO.
Table 1 Destabilization energies and bond lengths of H2 and CO in C60 and C58 cages Endohedral complex
Stabilizationa (kcal/mol)
H–H bond length A
C–O bond length A
H2 H2@C60 H2@C58 CO CO@C60 CO@C58
– 2.3 3.3 – 16.4 18.6
0.7348 0.7357 0.7339 – – –
– – – 1.1289 1.1281 1.1288
a Destabilization energy ¼ endohedral complex energy ) (guest molecule energy + fullerene cluster energy).
473
being in both cases endothermic. Although the endohedral complex of C60 with the H2 molecule was successfully synthesized using chemical ‘surgery’ methods [9,10], the preparation of endohedral complexes of C58 with H2 or CO constitutes still a challenge because macroscopic amounts of C58 are not yet available. However, Christian et al. [30] identified the formation of a C59 O cluster during the collision reaction of Oþ with C60 at an energy of 13 eV. They suggested that an endohedral complex of C58 with CO might constitute a possible form for the cluster. The H2 and CO molecules trapped inside the C58 cage have different orientations. As shown in Figs. 2a and b, the H2 molecular axis is normal to the face of the 7member ring, whereas the CO molecular axis is parallel to that face. Two factors are responsible for the orientations of H2 and CO molecules: the polarity of the molecule and its size. If the polarity would constitute the main factor, the CO molecule, which is weakly-polar, should orient in the direction of the highest dipole moment of the cage. However, the calculations revealed that the CO molecule did not orient in the direction of the highest dipole moment of C58 . Therefore, the orientation of the non-polar or weakly-polar molecule is mainly dependent on the guest molecular size. Because the C–O bond is much longer than the H–H bond, the former is oriented parallel to the face of the 7-member ring (the cage being the longest in that direction), while the latter is oriented normal to the face of the 7-member ring. To further confirm this explanation, we considered that CO2 , which is non-polar and much longer than CO, was captured inside the C58 . The optimized structure did show that the CO2 molecule has the same orientation inside the cage as CO. In addition, the C60 and the C58 cages have different effects on the bond lengths of the guest molecules. The H–H bond of the guest hydrogen molecule was shortened inside the C58 cage, whereas the length of the C–O bond remained unchanged. In conclusion, the C60 and the C58 cages exhibit similar performances in the formation of endohedral complexes with H2 and CO, namely, the C58 cage destabilizes the guest molecule trapped inside. H2 and CO molecules have different orientations, the molecular axis orientation of the former being normal to the face of the 7-member ring, whereas that of the latter parallel.
Fig. 2. Endohedral complexes of C58 with (a) H2 and (b) CO.
474
Y.H. Hu, E. Ruckenstein / Chemical Physics Letters 390 (2004) 472–474
Acknowledgements We are indebted to the reviewer for most helpful comments. References
[12] [13] [14] [15] [16] [17] [18]
[1] H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [2] J.R. Heath, S.C. O’Brien, Q. Zhang, Y. Liu, R.F. Curl, H.W. Kroto, F.K. Tittel, R.E. Smalley, J. Am. Chem. Soc. 107 (1985) 7779. [3] R.L. Murry, G.E. Scuseria, Science 263 (1994) 791. [4] M. Saunders, H.A. Jimenez-Vazquez, R.J. Cross, R.J. Poreda, Science 259 (1993) 1428. [5] S. Patchkovskii, W. Thiel, J. Am. Chem. Soc. 118 (1996) 7164. [6] J. Cioslowski, J. Am. Chem. Soc. 113 (1991) 4139. [7] M. B€ uhl, W. Thiel, H. Jiao, P. von Rague Schleyer, M. Saunders, F.A.L. Anet, J. Am. Chem. Soc. 116 (1994) 6005. [8] D.S. Bethune, R.D. Johnson, J.R. Salem, M.S. De Vries, Nature 366 (1993) 123. [9] Y. Rubin, T. Jarrosson, G. Wang, M.D. Bartberger, K.N. Houk, G. Schick, M. Saunders, R.J. Cross, Angew. Chem. Int. Ed. 40 (2001) 1543. [10] Y. Murata, M. Murata, K. Komatsu, J. Am. Chem. Soc. 125 (2003) 7152. [11] J.F. Nieregarten, Angew. Chem. Int. Ed. 40 (2001) 2973.
[19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]
J. Cioslowski, E. Fleischmann, J. Chem. Phys. 94 (1991) 3730. J. Cioslowski, A. Nanayakkara, J. Chem. Phys. 96 (1992) 8354. M.D. Newton, R.E. Stanton, J. Am. Chem. Soc. 108 (1986) 2469. R.L. Disch, J.M. Schulman, Chem. Phys. Lett. 125 (1986) 465. B.I. Dunlap, D.W. Brenner, J.W. Mintmire, R.C. Mowrey, C.T. White, J. Phys. Chem. 95 (1991) 5763. M. H€aser, J. Alml€ of, G.E. Scuseria, Chem. Phys. Lett. 181 (1991) 497. J.M. Hawkins, A. Meyer, T.A. Lewis, S.D. Loren, F.J. Hollander, Science 252 (1991) 312. K. Hedberg, L. Hedberg, D.S. Bethune, C.A. Brown, H.C. Dorn, R.D. Johnson, M. de Vries, Science 254 (1991) 410. C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785. I.V. Alabugin, M. Manoharan, B. Breiner, F.D. Lewis, J. Am. Chem. Soc. 125 (2003) 9329. J.K. Wolken, F. Turecek, J. Phys. Chem. A 103 (1999) 6268. Y.H. Hu, J. Am. Chem. Soc. 125 (2003) 4388. Y.H. Hu, E. Ruckenstein, J. Chem. Phys. 119 (2003) 10073. Y.H. Hu, E. Ruckenstein, J. Chem. Phys. 120 (2004) 7971. S.B. Boys, F. Bernardi, J. Mol. Phys. 19 (1970) 553. M.J. Frisch et al., GA U S S I A N 94, Revision E.1, Gaussian Inc., Pittsburgh, PA, 1995. S.C. Obrien, J.R. Heath, R.F. Curl, R.E. Smalley, J. Chem. Phys. 88 (1988) 220. R.L. Murry, D.L. Strout, G.L. Odom, G.E. Scuseria, Nature 366 (1993) 665. J.F. Christian, Z. Wan, S.L. Anderson, Chem. Phys. Lett. 199 (1992) 373.