Solvated Succinate Dianion: Structures, Electron Binding Energies, and Dyson Orbitals

Abstract

Structures and isomerization energies for the succinate dianion, O2C(CH2)2CO22-, in coordination with one or two water molecules are obtained from ab initio calculations. For the monohydrated case, the most stable structure has two hydrogen bonds between the water and one of the carboxylate groups in a bifurcated arrangement, while the next most stable structure places the water in a bridge between the carboxylate groups. Electron detachment energies obtained from electron propagator calculations agree closely with anion photoelectron spectra. Corresponding Dyson orbitals are most concentrated on carboxylate oxygens that are not directly involved in hydrogen bonds. For the dihydrated complex, the most stable structure has a water molecule coordinated to each carboxylate in a bifurcated arrangement, but there is a closely lying alternative in which there is one bifurcated water molecule coordinated to a carboxylate and another water molecule that bridges between the carboxylates. Predicted electron detachment energies are close to estimates that are made by extrapolation from experimental data on related hydrated dianions. Carboxylate oxygens make the largest contributions to the Dyson orbitals for the lowest electron detachment energies. In the alternative dihydrated structure, carboxylate oxygen amplitudes are reduced by the presence of hydrogen bonding in the Dyson orbitals for the lowest electron detachment energy.