ALBERT

Description: Computations for anion, dianions, and trianions of benzene are carried out to study the role of electron correlation in the polydeprotonation of benzene leading to benzene trianions both in the singlet and triplet states. The computations, while assessing the use of polarization and diffuse functions, are performed with Møller–Plesset second-order (MP2) perturbation theory and coupled-cluster theory up to the level of CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p), and with density functional theory (DFT) employing a hybrid, B3LYP, and a meta-hybrid, M05-2X, exchange-correlation functionals with Gaussian basis set 6-311++G(d,p) and correlation consistent basis set aug-cc-pVDZ. The deprotonation energies, including zero-point energy correction, of benzene anion and dianions are found to be highly sensitive to the quantum mechanical method and the basis set used. The formation of dianions and trianions, where the anionic centers lie adjacent to each other, is observed with unusual behavior in the deprotonation energy and the geometrical parameters obtained from the different level of the theories. The two exchange-correlation functionals compared show contrasting and unusual results for the trianionic species particularly for the triplet states, even if the diffuse functions are included in the basis set. Besides this, the ortho-dianion and 1,3,5-trianion are predicted to be ground-state triplet at CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) and DFT/M05-2X/6-311++G(d,p) levels, whereas DFT/B3LYP/6-311++G(d,p) predicts meta-dianion and 1,2,3-trianion to be ground-state triplet where all the anionic centers lie adjacent to each other. Copyright © 2014 John Wiley & Sons, Ltd. The presence of complicated inter-electronic interactions in polyanions of aromatic origin makes these systems highly challenging for the exchange-correlation functionals being developed in the density functional theory. In this study exploring polydeprotonation in benzene, contrasting and interesting trends in the deprotonation energies and geometries of singlet and triplet dianions and trianions of benzene are observed while comparing a hybrid and a meta-hybrid exchange-correlation functional.