We first consider the correlation of the PD properties with the nitrogen adsorption energy on Li, E(Li-N 2 ) (Fig. ). We observe that the Kamlet-Taft π * parameter and the pKa of the PDs show a moderate correlation with the strength of the nitrogen-lithium interaction. The acid dissociation constant (pKa) which is an indicator of electron-pair accepting activity for Lewis acids shows a negative correlation of -0.6 with the nitrogen-lithium interaction strength. This implies increasing pKa (and thus decreasing acidity) of the PD increases the adsorption strength of nitrogen on lithium.