Monomer and dimer complexes of coronene with atomic ions

Formation of ML+ and ML2+ complexes of coronene was investigated with 25 atomic ions (Mf) 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 Mf(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 ML2+ formation relative to coronene.