Microsolvation of small anions by aromatic molecules: An exploratory study

Abstract

This work was motivated by the experimental finding that the O 2 Ϫ /benzene interaction energy is unexpectedly large. To further explore the interactions of small anions with aromatic molecules, anion photoelectron spectroscopy was utilized to measure interaction strengths of the seed anions, O 2 Ϫ and NO Ϫ , complexed with several aromatic molecules, including benzene, naphthalene, pyridine, and pyrimidine. As in the case of O 2 Ϫ ͑benzene͒, the anion͑aromatic͒ 1 binding energies for the other complexes studied were also higher than one might have anticipated. In addition, the interaction energy of O 2 Ϫ complexed with a given aromatic molecule was, in every case studied, higher ͑by a factor of ϳ1.5͒ than that of NO Ϫ complexed with the same aromatic. While the dependence of interaction strengths on solvent dipole moments and/or polarizabilities implied a substantial electrostatic component to the binding in these complexes, differences in the binding of O 2 Ϫ and NO Ϫ with these aromatic molecules showed that there is a distinct covalent aspect to the interaction as well. A significant portion of this interaction was attributed to the fact that O 2 Ϫ and NO Ϫ are both open-shell anions that are interacting with closed-shell aromatic molecules. In the accompanying paper ͓J. Chem. Phys. 116, 9672 ͑2002͔͒ calculations on O 2 Ϫ ͑benzene͒ 1 by Jalbout and Adamowicz shed additional light on the nature of small anion-aromatic molecule interactions. Last, results are also presented comparing the interaction energies of several multisolvent, anionmolecule complexes.

The negative ion chemistry of nitric oxide in the gas phase

“…The reaction with benzene, a non-polar molecule with no electron affinity, proceeds only by collisional detachment (Rinden, Maricq, & Grabowski, 1989). Recent studies by Bowen and co-workers (Barbu et al, 2002) show that the NO À -pyridine cluster energy (0.62 eV) is slightly larger than the binding energy between NO À and benzene (0.44 eV).…”

Probing the Role of π Interactions in the Reactivity of Oxygen Species: A Case of Ethylzinc Aryloxides with Different Dispositions of Aromatic Rings toward the Metal Center

“…This situation is particularly surprising considering that, in general, the significant role of noncovalent interactions in various biochemical processes is well recognized, including those processes that involve π‐aromatic systems 4. Moreover, an interaction between aromatic molecules and O 2 was recognized in the 1950s,5a and this issue has been studied by various groups since5 (and also extended to interactions with the superoxide ${{\rm O}{{- \hfill \atop 2\hfill}}}$ radical) 6. Nevertheless, relatively little is known about the specific role of this type interaction in ROS transformations, and the introduction of π‐aromatic interactions into model systems for O 2 activation by metal complexes has not received a significant amount of attention.…”

Photoelectron spectroscopy of hydrated hexafluorobenzene anions

“…Electronic mail: kbowen@jhu.edu formed is aromatic and its solvent is a nonaromatic molecule, whereas in the latter cases, the roles are reversed. 18…”