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J . Phys. Chem. 1991, 95, 5768-5773
an incredibly rich set of new molecules of varying shape. Putting fluorine atoms inside the cage could also dramatically alter the response properties of C,Fm.
Acknowledgment. These calculations were made using a grant
of CRAY X-MP computer time from the US.Naval Research Laboratory. This work was supported in part by the Office of Naval Research (ONR) through the Naval Research Laboratory and through the ONR Chemistry and Materials Science Divisions Contracts NOOO14-91-WX-24150 and "14-91-WX-24154.
Structures and Vibrational Frequencies of Cbo,C,o, and C8, Krishnan Raghavachari* AT& T Bell Laboratories, Murray Hill, New Jersey 07974
and Celeste McMichael Roblfing* Sandia National Laboratories. Livermore, California 94551 -0969 (Received: March 28, 1991) The structures and vibrational frequencies of C, C7&and CMhave been determined with the semiempirical MNDO method. Two highly stable minimum-energy structures have been identified for CE4. Of the two, a D6h form, which contains five distinct carbon atoms, is found to be slightly more stable than a Td form with four distinct carbons. Both isomers are found to be significantly more stable than either Csoor C7,,, consistent with the presence of a greater proportion of six-membered rings in CE4.An additional structure containing seven-membered rings has also been considered for CM,but is significantly less stable than structures containly only five- and six-membered rings. Finally, the geometries of C, C70, and the two stable forms of CE4have been completely optimized by using ab initio Hartree-Fock theory with the double-f 3-21G basis set.
Introduction The recent macroscopic preparation' of spheroidal carbon clusters* has stimulated a wide variety of experimental and theoretical studies on these novel systems. C, and CT0have now been isolated by several different experimental groups and their properties have been m e a ~ u r e d . ~Many ' ~ theoretical studies have been reported on C, and a few on C70.'8-36Among the other
E. Nature 1985, 318, 162. (3) KrHtschmer, W.; Fostiropoulos, K.; Huffman, D. R. Chem. Phys. Leu. 1990, 170, 167. (4) Taylor, R.; Hare, J. P.; AMul-Sada, A. K.; Kroto, H. W. J . Chem. Soc., Chem. Commun. 1990, 1423. ( 5 ) Aije, H.; Alvarez, M. M.; Anz, S. J.; Beck, S. D.; Diederich, F.; Fostiropoulos, K.; Huffman, D. R.; Kritschmer, W.; Rubin, Y.; Schriver, K.; Sensharma, D.; Whetten, R. L. J . Phys. Chem. 1990,94, 8630. (6) Bethune, D. S.;Meijer, G.; Tang, W. C.; Rosen, H. J. Chem. Phys. Len. 1990, 174, 219. (7) Bethune, D. S.;Meijer, G.; Tang, W. C.; Rosen. H. J.; Golden, W. G.; Seki, H.; Brown, C. A.; deVrics, M.S . Chem. Phys. Lett. 1991, 179, 181. (8) Cox, D. M.; Bchal. S.;Disko, M.; Gorun, S.; Greaney, M.; Hsu, C. S.; Kollin, E.;Millar, J.; Robbins, J.; Robbins, W.; Sherwood, R.; Tindall, P. J . Am. Chem. Soc. 1991,113.2940. (9) Haufler, R. E.; Conceicao, J.; Chibante, L. P. F.; Chai, Y.; Byrne, N. E.; Flanagan, S.;Haley, M. M.; OBrien, S.C.; Pan, C.; Xiao, 2.;Billups, W. E.; Ciufolini, M. A.; Hauge, R. H.; Margrave, J. L.; Wilson, L. J.; Curl, R. F.; Smalley, R. E. J . Phys. Chem. 1990, 94, 8634. (IO) Haufler, R. E.; Chai, Y.; Chibante, L. P. F.; Conceicao, J.; Jin, C.; Wang, L.-S.; Maruyama, S.;Smalley, R. E. Mater. Res. Soc. Symp. Proc., in press. (11) Arbogast, J. W.; Darmanyan, A. P.; Foote, C. S.;Rubin, Y.; Diederich, F. N.; Alvarez. M.M.; Anz, S.J.; Whetten, R. L. J. Phys. Chem. 1991, 95, 1 1 . (12) Whetten. R. L.; Alvarez, M.M.; Anz, S. J.; Schriver, K. E.; Beck, R. D.; Diederich, F. N.;Rubin, Y.; Ettl, R.; Foote, C. S.;Darmanyan. A. P.; Arbogast, J. W. Mater. Res. Soc. Symp. Proc., in press. (13) Haddon, R. C.; Schneemeyer, L. F.; Waszczak, J. V.;Glarum,S. H.; Tycko, R.; Dabbagh, G.; Kortan, A. R.; Muller, A. J.; Mujsce, A. M.; Rosseinsky, M.J.; Zahurak, S.M.; Makhija, A. V.; Thiel, F. A.; Raghavachari, K.; Cockayne. E.; Elser, V. Nature 1991, 350,46. (14) Tycko. R.; Haddon. R. C.; Dabbagh, G.; Glarum, S.H.; Douglas, D. C.; Mujsce, A. M. J . Phys. Chem. 1991, 95, 518. ( I S ) Allemand, P. M.; Koch, A.; Wudl. F.; Rubin, Y.; Diederich, F.; Alvarez, M. M.; Anz, S.J.; Whetten, R. L. J . Am. Chem. Soc. 1991, 113, 1050. (16) Yannoni, C. S.; Johnson, R. D.; Meijer, G.; Bethune, D. S.;Salem, J . R. J . Phys. Chem. 1991, 95,9. (17) Yannoni, C. S.;et al. Materials Research Society Meeting, Boston, 1990.
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TABLE I: Bond Leugtbs (A) rad Bond Aagles (deg) for Cm param' MNDO HF/3-21G CI-CI 1.473 1.452 c1-Cl 1.402 I.370
cl-c3
c3-c3 c3-c4 C4C4
c4-cs cs-cs cI-cI-cI c,-cI-cl
c&-C3 c3c2-c3 c1c3-c3
CZ-C3
