A MP2(full) and CCSD(T) theoretical investigation on unusual cation-π interaction between OCBBCO and H+, Li+, Na+, Be2+ or Mg2+

The unusual and strong cation-pi interactions are found between cations (H+, Li+, Na+, Be2+, and Mg2+) and the electron-deficient B B bond using MP2(full) and CCSD(T) methods at 6-311+G(2df)(6-311++G(2df,2p) for H+ complexes) and aug-cc-pVTZ levels, accompanied by the B B bond contraction. A comparison with those between the corresponding cations and HC CH are also carried out. The binding energies follow the order of OCB BCO center dot center dot center dot H+ approximate to OCB BCO center dot center dot center dot Be2+ > OCB BCO center dot center dot center dot Mg2+ >> OCB BCO center dot center dot center dot Li+ > OCB BCO center dot center dot center dot Na+ and OCB BCO center dot center dot center dot cations > HC CH center dot center dot center dot cations at four levels. The atoms in molecules (AIM) theory has been applied to convince covalent interaction in the H+ complexes and confirm that the electron-deficient B B triple bond can be as the strong pi-electron donor in the cation-pi interaction. The analyses of natural bond orbital (NBO) and electron density shifts have revealed the nature of the cation-pi interaction and explained the origin of B B bond contraction. (C) 2009 Elsevier B.V. All rights reserved.