Competition of hydrogen, halogen, and pnicogen bonds in the complexes of HArF with XH2P (X=F, Cl, and Br).

A theoretical study of the complexes formed between HArF and XH2P (X=F, Cl, and Br) has been carried out using ab initio methods (MP2/aug-cc-pVDZ, MP2/aug-cc-pVTZ, and CCSD(T)/aug-cc-pVTZ). Three minima were found, which correspond to a hydrogen-bonded complex (I), a pnicogen-bonded complex (II), and a halogen-bonded complex (III). The pnicogen-bonded complex is the most stable, followed by the hydrogen-bonded complex, and the halogen-bonded complex is the least stable. The Ar-H bond is enhanced in FH2P-HArF-I complex and exhibits a blue shift, while it is weakened in ClH2P-HArF-I and BrH2P-HArF-I complexes and shows a red shift. A blue shift is also found for the distant Ar-H bond in the halogen-bonded and pnicogen-bonded complexes. These complexes have been understood with the electrostatic potentials and symmetry adapted perturbation theory (SAPT) method.