CRYSTAL-STRUCTURE OF THE TERT-BUTYL CATION

The structure of the tert-butyl cation (1) could be determined by an X-ray crystal structure analysis of its Sb2F11- salt at -80-degrees-C (P2(1), a = 6.123(2) angstrom, b = 13.758(4) angstrom, c = 7.614(4) angstrom, beta = 100.67(3)degrees; R = 0.029, R(w) = 0.029). Suitable crystals of 1.Sb2F11 were obtained only from a methylene chloride solution of the corresponding tert-pentyl salt by slow decomposition. The cation is planar within our limits of accuracy, the C+-C bonds have an average length of 1.442(5) angstrom, and the C-C+-C bond angles are 120(1)degrees. These results agree with the nutation NMR results of Yannoni, Myhre, et al. and recent ab initio results of Schleyer et al. In the crystal, the cation is surrounded by fluorine atoms from a total of eight counterions. The packing motif of cations and anions is similar to that of CsCl. Several other simple tertiary alkyl salts gave no suitable crystals for an X-ray structure determination.