Lithium−Benzene Sandwich Compounds:  A Quantum Chemical Study

Abstract

The structures and dissociation energies of Li n ·(C 6 H 6 ) n +1 sandwich complexes ( n = 1−6) have been investigated using quantum chemical techniques. At the G3(MP2) level of theory, the Li·(C 6 H 6 ) 2 complex exhibits a Jahn−Teller distortion, forming a D 2 h charge-separated species [C 6 H 6 -1/2 −Li + −C 6 H 6 -1/2 ] with a surprisingly large dissociation energy of 0.85 eV, and a short benzene−benzene distance of 3.54 Å. Comparisons are made with the Li·C 6 H 6, Li + ·C 6 H 6, and Li + ·(C 6 H 6 ) 2 complexes. The larger ( n > 1) complexes were studied at the B3LYP/6-31G(d) level and were also found to have large dissociation energies, ca. 0.85 eV per Li atom, and short benzene−benzene distances (3.70 Å).