A MP2(full) theoretical investigation on the π-halogen interaction between OCBBCO and X1X2 (X1, X2=F, Cl, Br)

The pi-halogen bond interactions are found between the B B triple bond and X1X2 (X1, X2 = F, Cl, Br) employing MP2( full) method at 6-311+G(2d), aug-cc-pVDZ and aug-cc-pVTZ levels according to the "CP (counterpoise) corrected potential energy surface (PES)" methodology, accompanied by the B B bond contraction. The (2,3) extrapolated energies using the two-point approximation are also reported. All the pi-halogen complexes are of electronic state (1)A(1) with the C-2V symmetry. The dipole moment of dihalogen, the effects of the polarization of the halogen atom X1 and the electron withdrawing of X2 influence the strength of pi-halogen bond interaction. The analyses of the natural charges, natural bond orbital (NBO), atoms in molecules (AIM) theory and electron density shifts reveal the nature of the pi-halogen bond interactions, and explain the origin of the B B bond contraction. The energy decomposition analysis at B3LYP/TZ2P level shows that the interaction energy in the OCB BCO center dot center dot center dot X1X2 is mainly determined by the orbital energy. The values of Delta E-int, Delta E-elstat, Delta E-pauli and Delta E-orb are all arranged in the order of OCB BCO center dot center dot center dot BrF > OCB BCO center dot center dot center dot ClF approximate to OCB BCO center dot center dot center dot FCl > OCB BCO center dot center dot center dot BrCl > OCB BCO center dot center dot center dot Br-2 > OCB BCO center dot center dot center dot Cl-2 > OCB BCO center dot center dot center dot ClBr > OCB BCO center dot center dot center dot FBr. The binding energy of the complex of OCB BCO with X1X2 is stronger than that of the corresponding HC CH center dot center dot center dot X1X2 complex. OCB BCO center dot center dot center dot F-2 is indicative of covalent interaction. These results confirm that OCB BCO can be as pi-electron donor to form the pi-halogen bond interaction. (C) 2010 Elsevier B.V. All rights reserved.