A theoretical study of X-H... and X... interactions in the complexes of furan, thiophene, pyrrole and hydrogen halides

By using ab initio geometry optimization calculations we obtained thirteen stable complexes containing H...pi and X...pi interactions between Furan, Thiophene, Pyrrole and HX (X = F, Cl, Br) at the MP2/6-311++G(3df,2pd) high level of theory. The interaction energies corrected for only ZPE and both ZPE and BSSE range from -7.92 to -28.47 kJ.mol(-1) and -3.28 to -22.33 kJ.mol(-1), respectively. The results show that for the same HX, the stability of complexes decreases in going from Pyrrole to Thiophene and finally to Furan moiety, and increases in the order of HF < HCl < HBr monomer with the same pi -system. The obtained results from AIM and MEP analyses indicate that the H...pi interaction is more stable than X...pi one in all the investigated complexes. It is found that the electrostatic, dispersion and induction energy terms significantly contribute to strength of the studied complexes, in which two formers are for H...pi hydrogen bonded complexes and two latters are for X...pi halogen bonded complexes.