A Theoretical Study on the Structures of the Cation-π Complexes Formed by Ethylene, Benzene with Li +, Na +, and K +

The structures of the cation-π complexes between ethylene, benzene and Li+, Na+, and K+ were studied systematically in detail for the first time. It was found that though the C-H bond of ethylene is elongated upon complexation as expected, the C-H bond of benzene is unexpectedly shortened upon complexation especially with lithium cation. Such a behavior might have the same physical origin as that in the recently found blue-shift hydrogen bonds.