Monocyclic carbon cluster ions Cn+· (n = 10 - 24) exhibit a specific reactivity towards benzene [1], nitriles [2], and unsaturated organic chlorides [3]. The cluster ions C11+·, C15+· and C19+· (general formula Cn+·, n = 4p+3) show a reduced reactivity for all these substrates while cluster ions C13+·, C17+· and C21+· (general formula Cn+·, n = 4p+1) are very reactive. This alteration of reactivity is attributed to different valence electronic situations in monocyclic cluster ions C(4p+3)+· and C(4p+1)+·. While the former are delocalized aromatic cyclic carbenium ions the latter ones are formally anti-aromatic and likely correspond to localized carbenium ions. A comparison of the reaction efficiency of these carbon cluster ions towards several nitriles suggests that the reactivity may depend on the ionization energy (IE) difference between cluster and substrate. This was now tested by investigating the ion/molecule reactions of selected carbon cluster ions with fluorinated benzenes C6H6-xFx (x = 0-6) and with pyridine C5H5N.
The cluster ions Cn+· were generated by electron impact induced dechlorination of appropriate polycyclic perchloroarenes in the external ion source of a Bruker CMS 47X FT-ICR instrument and reacted with the neutral substrate at a partial pressure between 5 x10-8 and 5 x10-7 mbar in the FT-ICR cell. The Cn+· (n = 10,12,13) react with C6H6-xFx by the formation of adduct ions Cn+6H6-xFx and by the loss of a hydrogen atom from these ions yielding C6+nH5-xFx. In secondary reactions both primary product ions add a further C6H6-xFx molecule. CA of the adduct ions results in the formation of fragment ions CpH2+·. Although the reaction efficiency decreases in particular for C13+· with F-substitution, it doesn't correlate well with the IE of the respective C6H6-xFx.
The ions Cn+· (n = 12,13,14) which are known to react efficiently with benzene [1] react also efficiently with pyridine by adding one and two C5H5N molecules. Only the second molecule is lost by CA of the adduct ions, and the first C5H5N is obviously bonded covalently to the carbon cluster ions. So far pyridine is the only substrate which exhibits reactivity with C24+· generated from perchlorocoronene. The reactions reveal clearly the presence of two isomers C24+·, one adding only a single C5H5N while the other isomer adds sequentially up to 5 C5H5N molecules.