Prereactive Complexes of Dihalogens XY with Lewis Bases B in the Gas Phase: A Systematic Case for the Halogen Analogue B⋅⋅⋅XY of the Hydrogen Bond B⋅⋅⋅HX

Similar and yet also notably different are the B small middle dot small middle dot small middle dotXY and B small middle dot small middle dot small middle dotHX complexes in the gas phase, where B is a simple Lewis base, XY is a homo- or heterodihalogen molecule, and HX is a hydrogen halide. This is demonstrated, for example, by the structures of oxirane small middle dot small middle dot small middle dotClF and oxirane small middle dot small middle dot small middle dotHCl (see picture). Both bonds are dominated by simple electrostatic interactions, but differ in terms of their propensity for nonlinearity.