Carbon cluster ions C-24(.+) have been generated from dodecachlorocoronene C24Cl12 by electron-impact ionization followed by collision-induced dissociation (CID) of the molecular ions C24Cl12.+ and fragment ions C24Clx+ using the technique of multiple-excitation collisional activation (MECA) and Fourier transform ion-cyclotron resonance spectrometry, The ions C-24(.+) were reacted with several organic reactants, but a fast reaction was observed only with pyridine, resulting in the addition of pyridine molecules. One fraction of the C-24(.+) cluster ions adds only a single pyridine molecule, and the adduct ion dissociates back to the starting material on CID. The remaining fraction adds up to five molecules of pyridine. CID of the product ion formed by addition of three pyridines shows that from this adduct ion none of the pyridine molecules is lost. It is suggested that the formation of two isomeric [C-24; Pyridine](+-) adduct ions is due to the presence of two isomeric C-24(.+) ions generated by MECA from C24Cl12.+ ions and fragment ions C24Clx+. For a comparison the reactions of C-n(.+) n = 12-14, with pyridine were investigated. These smaller carbon cluster ions were generated from appropriate perchloroarenes by exhaustive dechlorination by electron-impact ionization and are known to exist exclusively as monocyclic carbon rings. The reaction of these monocyclic C-n(.+) with pyridine proceeds also by addition of two or three pyridine molecules. Therefore, it is concluded that the C-24(.+) isomer, which reacts by multiple pyridine attachment, corresponds to an isomer with a monocyclic structure, in line with recent data from the literature, For the second C-24(.+) isomer a graphitic structure with the carbon skeleton of coronene is suggested. This C-24(.+) isomer undergoes fast reaction but adds only one pyridine molecule.