p-benzoquinone-benzene clusters as potential nanomechanical devices: A theoretical study.

The equilibrium structures and binding energies of the benzene complexes of p-benzoquinones (PBQ) and its negatively charged anionic species (PBQ^- and PBQ^2-) have been investigated theoretically using second-order Møller-Plesset calculations. While neutral p-benzoquinone-benzene clusters (PBQ-Bz) prefer to have a parallel displaced geometry (P-c), CH...π interactions (T-shaped geometries) prevail in the di-anionic PBQ-benzene (PBQ^2--Bz) complexes (T-e^2-). Studies on dianionic p-benzoquinone-benzene clusters showed that two nonbonded intermolecular interactions compete in the most stable conformation. One is H-bonding interaction (C–H...O type) between carbonyl oxygen of p-benzoquinone and one of the hydrogen atoms of benzene, and the other is a π–H interaction between π-electron cloud of PBQ^2- and another hydrogen atom of benzene. Blueshifted H-bonds were observed in T-shaped clusters. The changes in the geometrical preference of PBQ-Bz complex upon addition of electrons would be useful in designing optimized molecular mechanical devices based on the edge-to-face and face-to-face aromatic interactions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]