Cation-aromatic π interaction in the gas phase: an experimental study on relative silver (I) ion affinities of polyaromatic hydrocarbons

Abstract

Abundant silver (I) ion bound asymmetric dimers of polyaromatic hydrocarbons (PAHs) were easily generated by electrospray ionization. Based on the unimolecular decomposition of the Ag(I) ion bound asymmetric dimers, the relative Ag(I) ion affinities of nine PAHs in the gas phase has been established­as: benzene� <� naphthalene� <� phenanthrene� <� anthracene� <� fluoranthene� <� pyrene� <� triphenylene� <­chrysene < benz[a]anthracene. The observed Ag(I) ion affinities were found to correlate with calculated quadrupole moments of PAHs, indicating that electrostatic charge–quadrupole interaction is important in the cation–aromatic π binding of the polyaromatic systems being studied. However, secondary effects, such as surface area of the aromatic π electrons or intermolecular electronic repulsion and steric repulsion between bay region hydrogens, could also affect the magnitude and relative order of Ag(I) ion affinities of PAHs. © 1998 John Wiley & Sons, Ltd.