Complexation with the neutral base is exothermic in the gas phase and even more so in water where interaction energies can exceed 30 kcal mol-1.  In the gas phase, complexation is endothermic, but dissociation of the metastable dimer is obstructed by an energy barrier.  The complexation remains an exothermic process even after the large monomer deformation energy is factored in.
THERM