Ab Initio Investigation of Electron Detachment in Dicarboxylate Dianions

Abstract

Optimized structures for oxalate (C2O4), malonate (O2CCH2CO2), and succinate (O2C(CH2)2CO2) mono- and dianions are computed at the level of second-order Moller−Plesset perturbation theory (MP2). For oxalate, both anions exhibit D2d and D2h rotamers, and in addition, for the singly charged species, we find an anion−molecule complex of the form CO2-·CO2. For the malonate and succinate anions we examine both keto and enol isomers; the keto structures are characterized by unhindered rotation of the CO2 moieties about geometries of C2 symmetry, while the enol isomers are much more rigid as a result of an intramolecular hydrogen bond. In both malonate and succinate, the enol isomer is the more stable form of the monoanion, while the keto isomer is the more stable dianion, although for O2CCH2CO22- the estimated isomerization barrier is only about 7 kcal/mol. All of the dianions are adiabatically unbound and the enol dianions are vertically unbound as well. However, vertical detachment energies calculated by elec...