Are Halogen Bonded Structures Electrostatically Driven?

Halogen-bonded complexes B center dot center dot center dot XY, where B is a Lewis base and X a halogen atom, have been described as electrostatically driven, largely because of the close analogy between their structures and those of corresponding hydrogen-bonded complexes. Analysis of the components of the binding energy using symmetry-adapted perturbation theory suggests that while the main contribution to the binding is usually the electrostatic energy, the geometries are not always determined by electrostatics alone. In particular, the strong tendency to linearity of the B center dot center dot center dot XY bond is a consequence of exchange-repulsion, not electrostatics.