The geometries and binding energies of the complexes between C₄H₄Y (Y＝O, S, Se) and BX₃ (X＝H, F, Cl) have been calculated at the density function theory B3LYP and the second-order M?ller-Plesset theory MP2(full) levels. The vibration and natural bond orbital analyses were carried out, which indicate that the 18 conformers obtained include π-p interaction (the BX₃ locating exactly above the C＝C double bond) and n-p interaction (the boron atom directly combining to O, S or Se). The stabilities of C₄H₄Y-BH₃ complexes are in the order of n-p＞π-p. The stabilities of C₄H₄Y-BF₃ and C₄H₄Y-BCl₃ complexes with n-p interaction are relative to the π-p type complexes. The calculated results show that charge transfers, frequency shifts and change of geometries are relative to the stabilities of the complexes in the forming process.

Key words: density function theory, C₄H₄Y-BX₃ system, π-p interaction, n-p interaction