Inherent structures give insight into the structural changes that accompany the glass transition. Here, we present data on the energetics and configurations of inherent structures for various compositions in the NaCl-CsCl system, which are dominated by long-range ionic interactions. By choosing these compositions so as to achieve both crystallization and glass formation for a given system, the two types of structural developments can be contrasted. We evaluate the glass formation process for systems cooled at constant pressure on the basis of the temperature dependence of the inherent structure energies and inherent structure pressures. We find a minimum in the pressure-volume relation for the inherent structures obtained for isobarically cooled configurations, which closely tracks the glass transition of the simulated system. We also compare the inherent structure energies resulting from cooling under constant-volume conditions with those resulting from constant-pressure cooling. The pressure-volume work integrated along the inherent structure P-V curve is found to largely account for the differences between isobaric and isochoric inherent structure energies.