The Myth of "Anti-Electrostatic" Bonds

Some specific halogen- or hydrogen-bonded complexes between ions of like charge have been described as "anti-electrostatic." However, the analyses of the bonding in these complexes have not used a valid electrostatic model because, for instance, the effect of counterions has been neglected. Complete and appropriate ab initio and DFT studies are now reported that confirm that the observed complexes do not contradict an electrostatic model of their bonding, as must be the case. Indeed, a simple point-charge emulates the gas-phase behavior of the chloride ion interacting with an iodine-substituted anion to give a metastable minimum because of charge-dipole interactions. Inclusion of counterions in the calculations gives positive V_S(max) values at the iodine σ-hole. The effects of an empirical dispersion correction and solvation were investigated.