- Email: [email protected]
Theoretical study on C32 fullerenes and derivatives
Chemical Physics Letters 428 (2006) 148–151 www.elsevier.com/locate/cplett
Theoretical study on C32 fullerenes and derivatives Yingfei Chang a, Abraham F. Jalbout b, Jingping Zhang a, Zhongmin Su a, Rongshun Wang a,* a
Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, China b NASA Astrobiology Centers and the Department of Chemistry, the University of Arizona, Tucson, AZ 85721, USA Received 2 April 2006; in final form 22 June 2006 Available online 4 July 2006
Abstract A series of B3LYP/6-31G* calculations reveal that the D3 isomer is the most stable isomer of C32 carbon cages. The derivatives of it, 2þ including additional productions (C32H2, C32Cl2), hetero-fullerenes (C30B2, C30N2), isoelectronic molecules (C30 B2 2 , C30 N2 ) and dimers have been investigated at the same level. The results show that, the additional hydrogen atoms and replaced nitrogen atoms can enhance the electronic stabilization of D3 C32. Our calculations suggest that the building block of C32 oligomers which linked by sp3 bonds should be the saturated C32H2 unit. Ó 2006 Elsevier B.V. All rights reserved.
1. Introduction Fullerenes, serving as new agents and materials for molecular electronics, nanoprobes, superconductors, and non-linear optics [1–5], have caught the attention of chemists, physicists and material scientist since the discovery [6] and macroscopic scale synthesis [7] of C60. The most important and essential rule in governing the geometry of fullerenes is the isolated-pentagon rule (IPR) [8,9], which stating that the most stable fullerenes are those in which all pentagons are separated as far as possible with others and surrounded by five hexagons. However, it is impossible to satisfy this rule for lower fullerenes. It means that the socalled non-IPR fullerenes should be highly reactive and have unusual properties [10] due to the strained pentagon–pentagon fusions. In recent years, based on flexible and precise experimental techniques, lower fullerenes, which of course violate the IPR, became experimentally accessible, and the theoretical studies have also confirmed this [11–14]. In 1998, the C36 fullerene was claimed to have been produced in macro-
*
Corresponding author. Fax: +86 4315099511. E-mail address: [email protected] (R. Wang).
0009-2614/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2006.06.091
scopic quantities by DC arc-discharge method [15]. However, this process has not been recurred until now. In fact, C36 has only been isolated in its chemically saturated form as fullerene hydrides or oxyhydrides [16,17]. The smallest possible fullerene, C20, containing only 12 pentagons and no hexagon, was synthesized in 2000 [18], but only with a microsecond time scale in the condensed phase. Also, it was not until recently that the first smaller fullerene than C60, C50, has been synthesized in the solid state. Structural characterizations on C50 have been carried out by Xie and co-workers [19], in addition to theoretical studies aimed to assist characterization of this fullerene have been performed [20–22]. Among a variety of small fullerenes, one interesting and promising target is C32, which has a large band gap of 1.3 eV comparable to that of C70, as found by anion photoelectron spectroscopy [23]. So, it may be the next lower fullerene, which can be synthesized in the solid state after C50. In this Letter, the DFT method has been employed to confirm the most stable isomer of C32, and to investigate the electronic and chemical properties of it. Due to the non-IPR fullerenes may relieve strain by forming sp3 bond [24], the formation of derivatives based on the founded most stable isomer of C32 cage is to be expected, and the possibility of dimerization has been evaluated also.
Y. Chang et al. / Chemical Physics Letters 428 (2006) 148–151
2. Computational details All the isomers of C32 have been optimized by using the B3LYP/6-31G* method. The derivatives of D3 isomer (the most stable isomer of C32), like C32H2, C32Cl2, C30N2, 2þ C30B2, C30 B2 2 , C30 N2 , and dimers are also fully optimized in the given symmetry at the same level. The pyramidalization angle (hp) [25,26], which can be regarded as the magnitude of angle strain at a fullerene carbon atom is obtained by the MOL2MOL program [27]. All computations were performed using the GAUSSIAN03 suite of programs [28].
149
Table 1 Calculated relative energies (Erel, kJ/mol), HOMO–LUMO gap energies (Eg, eV), and n5/5 of C32 isomers Isomer
Symmetry
ERel
Eg
n5/5a
1 2 3 4 5 6 7 8
C2 D2 D3d C2 D3h D3 Oh D4d
227.2 273.3 308.1 108.0 326.6 0.0 644.5 1266.9
1.53 1.76 1.60 2.02 2.64 2.60 1.59 0.94
17 18 18 16 18 15 0 8
a
Pentagon–pentagon bond numbers.
3. Results and discussion 3.1. The most stable isomer of C32 cages All of the eight isomers for C32 cages were constructed as shown in Fig. 1, and numbered according to spiral algorithm [29]. The first six isomers are the classical fullerene structures, where the cage contains 12 pentagons and six hexagons. The last two isomers are therefore non-classical fullerene structures. Isomer 7 is nothing else than the leapfrog of cube [30] and consisted of 12 hexagons and six squares. The six squares in this structure are arranged as three perpendicular pairs to three orthogonal axes, and thus have Oh symmetry. Isomer 8 has D4d symmetry and formed by two squares, eight pentagons and eight hexagons. The calculated energies of all discussed cages relative to the D3 isomer are listed in Table 1. The results show that all
the fullerene structures have lower total energy than the non-fullerene structures, which is in agreement with the experimental result [31,32] that fullerenes are the most stable carbon clusters after C30. The D3 isomer, which has the minimal number of the shared pentagonal C–C bonds, has the lowest total energy and being considered as the most stable isomer. This is consistent with the results of Zhang’s [33] and Sun’s [34] which obtained by tight-binding molecular-dynamic total energy optimization and first-principles calculations, respectively. In addition, a large HOMO–LUMO energy gap (Eg) is associated with low chemical reactivity, because it is energetically unfavorable to extract electrons from the HOMO or add them to the LUMO, which would be necessary to activate a reaction. The calculated result shows that the isomer 6 has the largest Eg value except the isomer 5 which possess higher total energy. 3.2. Electronic character of C32H2, C32Cl2 and C30X2 (X = B, N)
Fig. 1. Eight isomers of C32 cage.
In D3 C32, there are two pentagon–pentagon–pentagon (PPP) fusion sites sharing one carbon atom, whereby considerable stain can be anticipated. The calculated pyramdalization angle (hp) is considered as a good measure of angle stain at a fullerene carbon atom. Therefore, the larger hp of an unsaturated carbon atom in a fullerene, the higher reactivity towards addition reactions is expected. Current calculations show that the hp of polar carbon atom for D3 C32 is 18.3°, much larger than that (11.6°) of C60, revealing the source of the major strain. Therefore, the two polar carbon atoms will function as the active sites in chemical reaction and will probably react favorably with other atoms. Both of the frontier molecular orbitals (Fig. 2) of D3 C32 are p orbitals, where the HOMO is built up by six 1,3-butadiene structures, and the LUMO appears to consist of a series of concentric circles as can be seen from the plot. At the two poles of the LUMO, there is conjugated action located on the polar side as well as the three linked carbon atoms, respectively. These sites can act as potential reactive sites in chemical mechanistic channels. As with other small fullerenes, the saturation and replacement of these highly
150
Y. Chang et al. / Chemical Physics Letters 428 (2006) 148–151
Fig. 2. Frontier molecular orbitals of D3 C32.
strained PPP sites with other atoms should be explored for comparison. The calculated results show that the added H and Cl atoms can release the straining energy of C32 by pyramidalization of the two polar carbons attached to sp3. The reaction of hydrogenation and chlorination are highly exothermic, with values of 253.48 and 260.72 kJ/mol, respectively. After the reaction takes place, the electronic stability can be enhanced by three naphthalenic subunits (Fig. 3). The effect of Cl atom on the frontier orbitals of D3 C32 is different from that of H. Compared with C32, the HOMO and LUMO energy of C32Cl2 is lowered by 0.11 eV, and as a result, C32 and C32Cl2 have the same energy gap of 2.60 eV. As opposed to C32Cl2 case, the HOMO and LUMO energy of C32H2 is higher than that of C32, by around 0.36 eV for the HOMO and 0.70 eV for LUMO. Accordingly, C32H2 has a larger energy gap of 2.94 eV (0.34 eV higher than that of C32). This higher energy gap shows that, the added two H atoms can remarkably stabilize the C32 fullerene. Due to the larger strain at the two poles of D3 C32, we can suppose that, if they replaced by other atoms, the sta-
Fig. 3. Structures of C32H2 (C32Cl2) and C30N2 (C30B2).
bility may change. Thus, the hetero-fullerene C30B2, C30N2, 2þ and the isoelectronic molecules of C32 (C30 B2 2 , C30 N2 ) have been investigated by the theoretical method (Fig. 3). Due to the fact that C30B2 has two electrons less than C32, it has a narrow energy gap (1.75 eV). However, its dianion, C30 B2 2 (isoelectronic with C32), has a wide energy gap (2.45 eV) comparable to that of C32. For C30N2, it has a wider energy gap (2.98 eV), which is more larger than that of C32. The C30N2 dication, C30 N2þ 2 , although isoelectronic with C32, is not energetic favorable, and has a much more narrow energy gap (1.54 eV). From our calculations, the hetero-fullerene C30 B2 and C30N2 should be stable, 2 and all of them have three well conjugated naphthalenic subunits. 3.3. Dimerization of D3 C32 The high strain at the two polar atoms of D3 C32 makes it an excellent candidate for the formation of a convalently bound fullerene solids similar to those formed in other small fullerenes such as C20 [11], C36 [35], and C50 [20]. In this Letter, two topological possibilities of the bare (unsaturated) dimerization modes are considered. The structures of them are shown in Fig. 4. The formal [2 + 2] dimerization mode is the most exothermic (73.1 kJ/mol) and is followed in energy by the single-bonded (C32)2 (42.0 kJ/mol) case. However, the two dimers are unstable as their narrow energy gaps suggest (1.88 and 0.51 eV, respectively) which are even smaller
Fig. 4. Structures of C32 based dimers.
Y. Chang et al. / Chemical Physics Letters 428 (2006) 148–151
than that of the monomer (2.60 eV). The saturated singlebonded (C32H)2, however, has a large HOMO–LUMO gap of 2.83 eV (0.23 eV higher than 2.60 eV for C32) as the additional H atom acts to release the strain. This molecule is a stable dimer, and the reaction for the formation of the hydrogenate (saturated) dimer (C32 )2 + H2 ! (C32 H)2 is found to be highly exothermic by around 397.0 kJ/mol. The hydrogen saturated [2 + 2] dimer converges into the single-bonded dimer after optimization. It is noteworthy that in both of the two single-bonded dimers, the C32 cage is not repeated along the C3 axis, but rotates 30° around it to assume a staggered orientation analogous to ethane. The larger energy gap as well as the high reaction energy of the hydrogen saturated dimmer suggests that the building block of C32 oligomers which linked by sp3 bonds should be composed of a saturated C32H2 unit. 4. Concluding remarks A systematic DFT study has been performed on the geometry and electronic properties of C32 isomers and derivatives. The D3 isomer has been confirmed as the most stable isomer of C32 fullerene potential energy surface. Due to the high intramolecular strain at the two polar carbon atoms on D3 C32, they will probably function as the active sites in various chemical reactions. The hetero-fullerene C30N2 and the isoelectronic molecule C30 B2þ 2 are the most favorable energetically configurations for C32. The hydrogen saturated C32H2 is more stable since the additional hydrogen atoms release the structure of excess torsional strain. As with other small fullerenes, C32 is also prone to polymerize, and further oligomerization or polymerization of C32 might produce novel one-dimensional polymer structures. Acknowledgement Financial support from the National Natural Science Foundation of China (No. 50473032) is gratefully acknowledged. References [1] M.S. Dresselhaus, G. Dresselhaus, P. Eklund, Science of Fullerenes and Carbon Nanotubes, Academic Press, New York, 1996.
151
[2] K. Holczer, O. Klein, S.M. Huang, R.B. Kaner, K.J. Fu, R.L. Whetten, F. Diederich, Science 252 (1991) 1154. [3] S. Pekker, A. Janossy, L. Mihaly, O. Chauvet, M. Carrard, L. Forro, Science 265 (1994) 1077. [4] R.E. Dinnebier, O. Gaunnarsson, H. Brumn, E. Koch, P.W. Stephens, A. Huq, M. Jansen, Science 296 (2002) 109. [5] W. Mickelson, S. Aloni, W.Q. Han, J. Cumings, A. Zettl, Science 300 (2003) 467. [6] H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [7] W. Kra¨tschmer, L.D. Lamb, K. Fostiropoulos, D.R. Huffman, Nature 347 (1990) 354. [8] H.W. Kroto, Nature 329 (1987) 529. [9] T.G. Schmalz, W.A. Seitz, D.J. Klein, G.E. Hite, J. Am. Chem. Soc. 110 (1998) 1113. [10] P.W. Fowler, T.J. Heine, Chem. Soc. Perkin Trans. 2001 (2001) 2487. [11] Z. Chen, T. Heine, H. Jiao, A. Hirsch, W. Thiel, P.v.R. Schleyer, Chem. Eur. J. 10 (2004) 963. [12] H.S. Wu, X.H. Xu, H.J. Jiao, J. Phys. Chem. A 108 (2004) 3813. [13] Y.F. Chang, J.P. Zhang, H. Sun, B. Hong, Z. An, R.S. Wang, Int. J. Quantum Chem. 105 (2005) 142. [14] X. Lu, Z. Chen, Chem. Rev. 105 (2005) 3643. [15] C. Piskoti, J. Yarger, A. Zettl, Nature 393 (1998) 771. [16] A. Koshio, M. Lnakuma, T. Sugai, H. Shinohara, J. Am. Chem. Soc. 122 (2000) 398. [17] A. Koshio, M. Lnakuma, Z.W. Wang, T. Sugai, H. Shinohara, J. Phys. Chem. B 104 (2000) 7908. [18] H. Prinzbach et al., Nature 407 (2000) 60. [19] S.Y. Xie et al., Science 304 (2004) 699. [20] X. Lu, Z. Chen, W. Thiel, P.v.R. Schleyer, R.B. Huang, L.S. Zheng, J. Am. Chem. Soc. 126 (2004) 14781. [21] L. Zhechkov, T. Heine, G. Seifert, J. Phys. Chem. A 108 (2004) 11733. [22] Y.F. Chang, J.P. Zhang, B. Hong, H. Sun, Z. An, R.S. Wang, J. Chem. Phys. 123 (2005) 094305. [23] H. Kietzmann, R. Rochow, G. Gantefo¨r, W. Eberhardt, K. Vietze, G. Seifert, P.W. Fowler, Phys. Rev. Lett. 81 (1998) 5378. [24] H.W. Kroto, D.R.M. Walton, Chem. Phys. Lett. 214 (1993) 353. [25] R.C. Haddon, Science 261 (1993) 1545. [26] R.C. Haddon, J. Phys. Chem. A 105 (2001) 4164. [27] T.E. Gunda, MOL2MOL version 5.3, University of Debrecen, Debrecen, Hungary, 2004. [28] M.J. Frisch et al., GAUSSIAN 03, Gaussian Inc., Pittsburgh PA, 2003. [29] P.W. Fowler, D.E. Manolopoulos, An Atlas of Fullerenes, Clarendon Press, Oxford, 1995. [30] M.V. Diudea, P.E. John, A. Graovac, M. Primorac, T. Pisanski, Croat. Chem. Acta 76 (2003) 153. [31] H. Handschuh, G. Ganterfo¨r, B. Kessler, P.S. Bechthold, W. Eberhardt, Phys. Rev. Lett. 75 (1995) 1095. [32] R.O. Jones, G. Seifert, Phys. Rev. Lett. 79 (1997) 443. [33] B.L. Zhang, C.Z. Wang, K.M. Ho, C.H. Xu, C.T. Chan, J. Chem. Phys. 97 (1992) 5007. [34] Q. Sun, Q. Wang, J.Z. Yu, K. Ohno, Y. Kawazoe, J. Phys.-Condens. Matter 13 (2001) 1931. [35] P.W. Fowler, D. Mitchell, F. Zerbetto, J. Am. Chem. Soc. 121 (1999) 3218.
Theoretical study on C32 fullerenes and derivatives Yingfei Chang a, Abraham F. Jalbout b, Jingping Zhang a, Zhongmin Su a, Rongshun Wang a,* a
Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, China b NASA Astrobiology Centers and the Department of Chemistry, the University of Arizona, Tucson, AZ 85721, USA Received 2 April 2006; in final form 22 June 2006 Available online 4 July 2006
Abstract A series of B3LYP/6-31G* calculations reveal that the D3 isomer is the most stable isomer of C32 carbon cages. The derivatives of it, 2þ including additional productions (C32H2, C32Cl2), hetero-fullerenes (C30B2, C30N2), isoelectronic molecules (C30 B2 2 , C30 N2 ) and dimers have been investigated at the same level. The results show that, the additional hydrogen atoms and replaced nitrogen atoms can enhance the electronic stabilization of D3 C32. Our calculations suggest that the building block of C32 oligomers which linked by sp3 bonds should be the saturated C32H2 unit. Ó 2006 Elsevier B.V. All rights reserved.
1. Introduction Fullerenes, serving as new agents and materials for molecular electronics, nanoprobes, superconductors, and non-linear optics [1–5], have caught the attention of chemists, physicists and material scientist since the discovery [6] and macroscopic scale synthesis [7] of C60. The most important and essential rule in governing the geometry of fullerenes is the isolated-pentagon rule (IPR) [8,9], which stating that the most stable fullerenes are those in which all pentagons are separated as far as possible with others and surrounded by five hexagons. However, it is impossible to satisfy this rule for lower fullerenes. It means that the socalled non-IPR fullerenes should be highly reactive and have unusual properties [10] due to the strained pentagon–pentagon fusions. In recent years, based on flexible and precise experimental techniques, lower fullerenes, which of course violate the IPR, became experimentally accessible, and the theoretical studies have also confirmed this [11–14]. In 1998, the C36 fullerene was claimed to have been produced in macro-
*
Corresponding author. Fax: +86 4315099511. E-mail address: [email protected] (R. Wang).
0009-2614/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2006.06.091
scopic quantities by DC arc-discharge method [15]. However, this process has not been recurred until now. In fact, C36 has only been isolated in its chemically saturated form as fullerene hydrides or oxyhydrides [16,17]. The smallest possible fullerene, C20, containing only 12 pentagons and no hexagon, was synthesized in 2000 [18], but only with a microsecond time scale in the condensed phase. Also, it was not until recently that the first smaller fullerene than C60, C50, has been synthesized in the solid state. Structural characterizations on C50 have been carried out by Xie and co-workers [19], in addition to theoretical studies aimed to assist characterization of this fullerene have been performed [20–22]. Among a variety of small fullerenes, one interesting and promising target is C32, which has a large band gap of 1.3 eV comparable to that of C70, as found by anion photoelectron spectroscopy [23]. So, it may be the next lower fullerene, which can be synthesized in the solid state after C50. In this Letter, the DFT method has been employed to confirm the most stable isomer of C32, and to investigate the electronic and chemical properties of it. Due to the non-IPR fullerenes may relieve strain by forming sp3 bond [24], the formation of derivatives based on the founded most stable isomer of C32 cage is to be expected, and the possibility of dimerization has been evaluated also.
Y. Chang et al. / Chemical Physics Letters 428 (2006) 148–151
2. Computational details All the isomers of C32 have been optimized by using the B3LYP/6-31G* method. The derivatives of D3 isomer (the most stable isomer of C32), like C32H2, C32Cl2, C30N2, 2þ C30B2, C30 B2 2 , C30 N2 , and dimers are also fully optimized in the given symmetry at the same level. The pyramidalization angle (hp) [25,26], which can be regarded as the magnitude of angle strain at a fullerene carbon atom is obtained by the MOL2MOL program [27]. All computations were performed using the GAUSSIAN03 suite of programs [28].
149
Table 1 Calculated relative energies (Erel, kJ/mol), HOMO–LUMO gap energies (Eg, eV), and n5/5 of C32 isomers Isomer
Symmetry
ERel
Eg
n5/5a
1 2 3 4 5 6 7 8
C2 D2 D3d C2 D3h D3 Oh D4d
227.2 273.3 308.1 108.0 326.6 0.0 644.5 1266.9
1.53 1.76 1.60 2.02 2.64 2.60 1.59 0.94
17 18 18 16 18 15 0 8
a
Pentagon–pentagon bond numbers.
3. Results and discussion 3.1. The most stable isomer of C32 cages All of the eight isomers for C32 cages were constructed as shown in Fig. 1, and numbered according to spiral algorithm [29]. The first six isomers are the classical fullerene structures, where the cage contains 12 pentagons and six hexagons. The last two isomers are therefore non-classical fullerene structures. Isomer 7 is nothing else than the leapfrog of cube [30] and consisted of 12 hexagons and six squares. The six squares in this structure are arranged as three perpendicular pairs to three orthogonal axes, and thus have Oh symmetry. Isomer 8 has D4d symmetry and formed by two squares, eight pentagons and eight hexagons. The calculated energies of all discussed cages relative to the D3 isomer are listed in Table 1. The results show that all
the fullerene structures have lower total energy than the non-fullerene structures, which is in agreement with the experimental result [31,32] that fullerenes are the most stable carbon clusters after C30. The D3 isomer, which has the minimal number of the shared pentagonal C–C bonds, has the lowest total energy and being considered as the most stable isomer. This is consistent with the results of Zhang’s [33] and Sun’s [34] which obtained by tight-binding molecular-dynamic total energy optimization and first-principles calculations, respectively. In addition, a large HOMO–LUMO energy gap (Eg) is associated with low chemical reactivity, because it is energetically unfavorable to extract electrons from the HOMO or add them to the LUMO, which would be necessary to activate a reaction. The calculated result shows that the isomer 6 has the largest Eg value except the isomer 5 which possess higher total energy. 3.2. Electronic character of C32H2, C32Cl2 and C30X2 (X = B, N)
Fig. 1. Eight isomers of C32 cage.
In D3 C32, there are two pentagon–pentagon–pentagon (PPP) fusion sites sharing one carbon atom, whereby considerable stain can be anticipated. The calculated pyramdalization angle (hp) is considered as a good measure of angle stain at a fullerene carbon atom. Therefore, the larger hp of an unsaturated carbon atom in a fullerene, the higher reactivity towards addition reactions is expected. Current calculations show that the hp of polar carbon atom for D3 C32 is 18.3°, much larger than that (11.6°) of C60, revealing the source of the major strain. Therefore, the two polar carbon atoms will function as the active sites in chemical reaction and will probably react favorably with other atoms. Both of the frontier molecular orbitals (Fig. 2) of D3 C32 are p orbitals, where the HOMO is built up by six 1,3-butadiene structures, and the LUMO appears to consist of a series of concentric circles as can be seen from the plot. At the two poles of the LUMO, there is conjugated action located on the polar side as well as the three linked carbon atoms, respectively. These sites can act as potential reactive sites in chemical mechanistic channels. As with other small fullerenes, the saturation and replacement of these highly
150
Y. Chang et al. / Chemical Physics Letters 428 (2006) 148–151
Fig. 2. Frontier molecular orbitals of D3 C32.
strained PPP sites with other atoms should be explored for comparison. The calculated results show that the added H and Cl atoms can release the straining energy of C32 by pyramidalization of the two polar carbons attached to sp3. The reaction of hydrogenation and chlorination are highly exothermic, with values of 253.48 and 260.72 kJ/mol, respectively. After the reaction takes place, the electronic stability can be enhanced by three naphthalenic subunits (Fig. 3). The effect of Cl atom on the frontier orbitals of D3 C32 is different from that of H. Compared with C32, the HOMO and LUMO energy of C32Cl2 is lowered by 0.11 eV, and as a result, C32 and C32Cl2 have the same energy gap of 2.60 eV. As opposed to C32Cl2 case, the HOMO and LUMO energy of C32H2 is higher than that of C32, by around 0.36 eV for the HOMO and 0.70 eV for LUMO. Accordingly, C32H2 has a larger energy gap of 2.94 eV (0.34 eV higher than that of C32). This higher energy gap shows that, the added two H atoms can remarkably stabilize the C32 fullerene. Due to the larger strain at the two poles of D3 C32, we can suppose that, if they replaced by other atoms, the sta-
Fig. 3. Structures of C32H2 (C32Cl2) and C30N2 (C30B2).
bility may change. Thus, the hetero-fullerene C30B2, C30N2, 2þ and the isoelectronic molecules of C32 (C30 B2 2 , C30 N2 ) have been investigated by the theoretical method (Fig. 3). Due to the fact that C30B2 has two electrons less than C32, it has a narrow energy gap (1.75 eV). However, its dianion, C30 B2 2 (isoelectronic with C32), has a wide energy gap (2.45 eV) comparable to that of C32. For C30N2, it has a wider energy gap (2.98 eV), which is more larger than that of C32. The C30N2 dication, C30 N2þ 2 , although isoelectronic with C32, is not energetic favorable, and has a much more narrow energy gap (1.54 eV). From our calculations, the hetero-fullerene C30 B2 and C30N2 should be stable, 2 and all of them have three well conjugated naphthalenic subunits. 3.3. Dimerization of D3 C32 The high strain at the two polar atoms of D3 C32 makes it an excellent candidate for the formation of a convalently bound fullerene solids similar to those formed in other small fullerenes such as C20 [11], C36 [35], and C50 [20]. In this Letter, two topological possibilities of the bare (unsaturated) dimerization modes are considered. The structures of them are shown in Fig. 4. The formal [2 + 2] dimerization mode is the most exothermic (73.1 kJ/mol) and is followed in energy by the single-bonded (C32)2 (42.0 kJ/mol) case. However, the two dimers are unstable as their narrow energy gaps suggest (1.88 and 0.51 eV, respectively) which are even smaller
Fig. 4. Structures of C32 based dimers.
Y. Chang et al. / Chemical Physics Letters 428 (2006) 148–151
than that of the monomer (2.60 eV). The saturated singlebonded (C32H)2, however, has a large HOMO–LUMO gap of 2.83 eV (0.23 eV higher than 2.60 eV for C32) as the additional H atom acts to release the strain. This molecule is a stable dimer, and the reaction for the formation of the hydrogenate (saturated) dimer (C32 )2 + H2 ! (C32 H)2 is found to be highly exothermic by around 397.0 kJ/mol. The hydrogen saturated [2 + 2] dimer converges into the single-bonded dimer after optimization. It is noteworthy that in both of the two single-bonded dimers, the C32 cage is not repeated along the C3 axis, but rotates 30° around it to assume a staggered orientation analogous to ethane. The larger energy gap as well as the high reaction energy of the hydrogen saturated dimmer suggests that the building block of C32 oligomers which linked by sp3 bonds should be composed of a saturated C32H2 unit. 4. Concluding remarks A systematic DFT study has been performed on the geometry and electronic properties of C32 isomers and derivatives. The D3 isomer has been confirmed as the most stable isomer of C32 fullerene potential energy surface. Due to the high intramolecular strain at the two polar carbon atoms on D3 C32, they will probably function as the active sites in various chemical reactions. The hetero-fullerene C30N2 and the isoelectronic molecule C30 B2þ 2 are the most favorable energetically configurations for C32. The hydrogen saturated C32H2 is more stable since the additional hydrogen atoms release the structure of excess torsional strain. As with other small fullerenes, C32 is also prone to polymerize, and further oligomerization or polymerization of C32 might produce novel one-dimensional polymer structures. Acknowledgement Financial support from the National Natural Science Foundation of China (No. 50473032) is gratefully acknowledged. References [1] M.S. Dresselhaus, G. Dresselhaus, P. Eklund, Science of Fullerenes and Carbon Nanotubes, Academic Press, New York, 1996.
151
[2] K. Holczer, O. Klein, S.M. Huang, R.B. Kaner, K.J. Fu, R.L. Whetten, F. Diederich, Science 252 (1991) 1154. [3] S. Pekker, A. Janossy, L. Mihaly, O. Chauvet, M. Carrard, L. Forro, Science 265 (1994) 1077. [4] R.E. Dinnebier, O. Gaunnarsson, H. Brumn, E. Koch, P.W. Stephens, A. Huq, M. Jansen, Science 296 (2002) 109. [5] W. Mickelson, S. Aloni, W.Q. Han, J. Cumings, A. Zettl, Science 300 (2003) 467. [6] H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [7] W. Kra¨tschmer, L.D. Lamb, K. Fostiropoulos, D.R. Huffman, Nature 347 (1990) 354. [8] H.W. Kroto, Nature 329 (1987) 529. [9] T.G. Schmalz, W.A. Seitz, D.J. Klein, G.E. Hite, J. Am. Chem. Soc. 110 (1998) 1113. [10] P.W. Fowler, T.J. Heine, Chem. Soc. Perkin Trans. 2001 (2001) 2487. [11] Z. Chen, T. Heine, H. Jiao, A. Hirsch, W. Thiel, P.v.R. Schleyer, Chem. Eur. J. 10 (2004) 963. [12] H.S. Wu, X.H. Xu, H.J. Jiao, J. Phys. Chem. A 108 (2004) 3813. [13] Y.F. Chang, J.P. Zhang, H. Sun, B. Hong, Z. An, R.S. Wang, Int. J. Quantum Chem. 105 (2005) 142. [14] X. Lu, Z. Chen, Chem. Rev. 105 (2005) 3643. [15] C. Piskoti, J. Yarger, A. Zettl, Nature 393 (1998) 771. [16] A. Koshio, M. Lnakuma, T. Sugai, H. Shinohara, J. Am. Chem. Soc. 122 (2000) 398. [17] A. Koshio, M. Lnakuma, Z.W. Wang, T. Sugai, H. Shinohara, J. Phys. Chem. B 104 (2000) 7908. [18] H. Prinzbach et al., Nature 407 (2000) 60. [19] S.Y. Xie et al., Science 304 (2004) 699. [20] X. Lu, Z. Chen, W. Thiel, P.v.R. Schleyer, R.B. Huang, L.S. Zheng, J. Am. Chem. Soc. 126 (2004) 14781. [21] L. Zhechkov, T. Heine, G. Seifert, J. Phys. Chem. A 108 (2004) 11733. [22] Y.F. Chang, J.P. Zhang, B. Hong, H. Sun, Z. An, R.S. Wang, J. Chem. Phys. 123 (2005) 094305. [23] H. Kietzmann, R. Rochow, G. Gantefo¨r, W. Eberhardt, K. Vietze, G. Seifert, P.W. Fowler, Phys. Rev. Lett. 81 (1998) 5378. [24] H.W. Kroto, D.R.M. Walton, Chem. Phys. Lett. 214 (1993) 353. [25] R.C. Haddon, Science 261 (1993) 1545. [26] R.C. Haddon, J. Phys. Chem. A 105 (2001) 4164. [27] T.E. Gunda, MOL2MOL version 5.3, University of Debrecen, Debrecen, Hungary, 2004. [28] M.J. Frisch et al., GAUSSIAN 03, Gaussian Inc., Pittsburgh PA, 2003. [29] P.W. Fowler, D.E. Manolopoulos, An Atlas of Fullerenes, Clarendon Press, Oxford, 1995. [30] M.V. Diudea, P.E. John, A. Graovac, M. Primorac, T. Pisanski, Croat. Chem. Acta 76 (2003) 153. [31] H. Handschuh, G. Ganterfo¨r, B. Kessler, P.S. Bechthold, W. Eberhardt, Phys. Rev. Lett. 75 (1995) 1095. [32] R.O. Jones, G. Seifert, Phys. Rev. Lett. 79 (1997) 443. [33] B.L. Zhang, C.Z. Wang, K.M. Ho, C.H. Xu, C.T. Chan, J. Chem. Phys. 97 (1992) 5007. [34] Q. Sun, Q. Wang, J.Z. Yu, K. Ohno, Y. Kawazoe, J. Phys.-Condens. Matter 13 (2001) 1931. [35] P.W. Fowler, D. Mitchell, F. Zerbetto, J. Am. Chem. Soc. 121 (1999) 3218.