N lone-pair⋯π interaction: a rotational study of chlorotrifluoroethylene⋯ammonia

The rotational spectra of four isotopologues of the adduct C2F3Cl–NH3 show that NH3 is bound to the partner molecule through a (N)lone-pair⋯π interaction. Ammonia is located in proximity to the C2 atom (the one linked to two fluorine atoms), with the C2⋯N distance = 2.987(2) A. The nuclear hyperfine structure due to the quadrupole coupling effects of 35Cl/37Cl and 14N nuclei has been fully resolved. The 14N quadrupole coupling constants allow estimating the effective orientation of NH3 in the complex.