Laser vaporization experiments with graphite in a supersonic cluster beam apparatus indicate that the smallest fullerene to form in substantial abundance is C(28). Although ab initio quantum chemical calculations predict that this cluster will favor a tetrahedral cage structure, it is electronically open shell. Further calculations reveal that C(28) in this structure should behave as a sort of hollow superatom with an effective valence of 4. This tetravalence should be exhibited toward chemical bonding both on the outside and on the inside of the cage. Thus, stable closed-shell derivatives of C(28) with large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps should be attainable either by reacting at the four tetrahedral vertices on the outside of the C(28) cage to make, for example, C(28)H(4), or by trapping a tetravalent atom inside the cage to make endothedral fullerenes such as Ti@C(28). An example of this second, inside route to C(28) stabilization is reported here: the laser and carbon-arc production of U@C(28).

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Intramolecular charge separation (CS) and charge recombination (CR) processes of the dyad molecule linking C 60 and N,N-di(6-tert-butylbiphenyl)benzenamine (BBA) were investigated by pico-and nanosecond laser flash photolysis methods. Furthermore, intermolecular electron transfer to a methanofullerene (C 61 H 2 ) was also investigated; the electron-transfer rate between triplet excited C 61 H 2 and BBA was somewhat slower than that of C 60 due to less negative reduction potential of C 61 H 2 . As for the BBA-C 60 dyad molecule, CS was successfully observed in polar solvents by excitation of C 60 moiety with picosecond laser pulse, while only the intersystem crossing was observed in nonpolar solvent. The CS process in the Marcus "normal region" was confirmed. In moderately polar solvent, radical ion pairs recombined within a few nanoseconds to generate the ground state and the triplet excited state of the C 60 -moiety. On the other hand, in polar solvents, the radical ion pairs decayed by two-steps: Most part decayed within 1 ns, while the radical ions were also observed in the submicrosecond region for a ca. 10% yield of generated BBA •+ -C 60 •-. An equilibrium between CS and triplet states was proposed for the mechanism of long-lived CS state.

tially separate components. The role of ion-molecule complexes has long been postulated in mass ~pectrometry,['~] but was based. in general. on indirect evidence from the fragmentation pattern of excited species from the ionization of molecules in which the putative components of the complex were initially covalently bound. In the specific case of alkylbenzenes. irrefutable mass spectrometric evidence is lacking for complexes such iis 2; results of molecular orbital ~alculations'~"~ do not appear inconsistent with ours.The gmcous s:iinpIc\ fix the radiolytic experimenls were prepared in se;iled 135 mL glass \cssels. iri-.idiatrd in a 220 Gainmacell (Nuclear Canada Ltd.). fitted with a thernio\tat. The gaseh and the chemicals used were research-grade products from coininti-cia1 source\. The radiolytic products were analyzed h) GC;MS (50 m long. 0.2 inin i . d fuxd d i c a column, coated with a 0.5 pm methylsilicons tilni: VG Micronia\?, TRIO quadrupolc mass spectrometer). The FT-ICR experiments were pcrlorinrd with .I Brukcr Spectrospin Apex TM 47e spectrometer equipped with a n exteriii ion miircc

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Spiroannelated methanofullerenes bearing quinone-type addends including TCNQ and DCNQI analogues (3a − c, 6a,b, 8, 10, and 11) have been prepared, and their structural and electronic properties have been characterized by both experimental techniques and quantum-chemical calculations. The spiro[2,5-cyclohexadienone-4,61‘-methanofullerene] derivatives (3a − c), the spiro[10-anthrone-9,61‘-methanofullerene] (8), and the TCNQ- and DCNQI-type derivatives (10 and 11) were isolated as [6,6] adducts. The spiro[cyclohexanone-4,61‘-methanofullerene] (6) was however obtained as a mixture of [5,6] and [6,6] isomers. The novel methanofullerenes, with the only exception of 6, show irreversible cyclic voltammograms with additional reduction peaks. The conjugated cyclohexadienone derivatives 3 exhibit better acceptor abilities than the parent C60. Semiempirical PM3 calculations show that the addend lies perpendicular to the transanular bond in 3, while it folds down and adopts a butterfly shaped structure for compounds 8, 10, and 11. For compounds 3, periconjugative interactions transmit the inductive effect of the addend and produce a small stabilization of the orbitals of C60, resulting in a less negative first-reduction potentials compared to C60. For compounds 8, 10, and 11, the folding of the addend prevents periconjugative effects. Theoretical calculations performed on 3a • - and 3a 2- at the semiempirical (PM3), density functional (B3P86/3-21G), and ab initio (HF/6-31G*) levels indicate that the attachment of the first electron causes the homolytic cleavage of one of the bonds connecting the addend to C60. The resulting open-cyclopropane structure is stabilized by the aromaticity of the phenoxyl radical structure presented by the addend. The second electron enters in the addend forming the phenoxyl anion. This ring opening is supported by ESR measurements and explains the irreversible electrochemical behavior of compounds 3. The nonconjugated nature of the cyclohexanone ring in 6 determines that reduction takes place via a closed-cyclopropane structure with an electrochemical behavior similar to that observed for C60. Compounds 8, 10, and 11 are proposed to undergo reduction via an open-cyclopropane structure now obtained after the attachment of the second electron which produces the heterolytic opening of the cyclopropane ring. The lack of planarity shifts the reduction of the addend to more negative potentials.