Monomer and Dimer Complexes of Coronene with Atomic Ions

Formation of ML + and ML 2 + complexes of coronene was investigated with 25 atomic ions (M + ) in the low-pressure gas-phase environment of the Fourier-transform ion cyclotron resonance (FT-ICR) ion trapping mass spectrometer. All of the atomic ions formed M + (Cor) except the alkalis (and also excepting a few cases which were dominated by charge transfer). All the other cases reacted with large, collisionally saturated rates, implying bond strengths >35 kcal mol - 1, except for the larger alkaline earths Sr + and Ba +, whose noticeably slower rates were attributed to relatively lower bond strengths around 32 kcal mol - 1 . Many of the M + (Cor) complexes reacted further to M + (Cor) 2 with collisionally saturated rates, but several cases (Mg +, Al +, Si +, In +, Pb +, Bi + ) reacted more slowly or not at all, indicating weaker bonds. The important role of transition-metal character in M + (Cor) 2 bonding is suggested by the observation that transition metal ions (Sc + and Mn +, for instance) rapidly formed M + (Cor) 2 complexes, while comparable non-transition ions (Mg +, Al +, Si + ) did so poorly or not at all. The rates of formation of the various complexes were interpreted to estimate ion−neutral bond strengths, or at least to give upper or lower limits to the bond strengths. Atomic-ion/benzene bond strengths were generally well correlated in a qualitative way with the observed patterns of formation of ion/coronene complexes. Comparison with the isomeric ligand tribenzocyclyne (TBC) supports the interpretation that small ions (Ni +, Cu + ) partially insert into the cavity of TBC, resulting in inhibited ML 2 + formation relative to coronene.