The hydrogen bond energies of the bihalide ions XHX− and YHX−

Experimental measurements of the gas phase ion equilibria X− + HX = XHX−, X−(HX)n−1 + HX = X−(HX)n, and X− + HY = XHY where X, Y = Cl, Br, I, with a high pressure mass spectrometer, combined with the recent determination of F− + HF = FHF− by Larson and McMahon, provide a very complete set of hydrogen bond dissociation enthalpies and free energies for the hydrogen bihalide ions. The bond energy trends in the different XHX− and XHY− are discussed. The data can be used also for the evaluation of lattice energies of salts containing the bihalide ions and for determinations of the solvation energies of these ions.