General conclusions concerning the nature of the B ClF interaction follow from the behaviour of the properties of sixteen gas-phase complexes as the Lewis base B varies. Electric charge redistribution within ClF is small for most B ClF considered (Mulliken outer complexes) but examples of the inner type [BCl] + F - having significant charge transfer are identified. Angular geometries in the series B ClF and B HCl are strikingly parallel. However, when the symmetry is C s , the Z H-Cl systems (Z = acceptor atom) are significantly nonlinear while the Z Cl-F are all nearly collinear. Rules for predicting angular geometries in B HCl are refined and extended to B ClF.