{insert Table 3}
The electron densities (ρ (r)) and Laplacian of the electron densities (∇2ρ (r)) of the H+···O- interactions (involving ammonium and carboxylate groups) are 0.215 to 0.277 e Å-3 and 2.610 to 3.041 e Å-5. The corresponding values for H+···O interactions are ranging from 0.114 to 0.227 e Å-3 and 1.79 to 2.796 e Å-5. The ρ (r) and ∇2ρ (r) values are slightly lower for N–H+···Owater interactions as compared to other N–H+···O/O-interactions. The theoretical ρ (r) and ∇2ρ (r) values for these interactions are comparable to those of values obtained from experimental charge densities studies.41Moreover, both ρ (r) and ∇2ρ (r) values for the intermolecular N–H+···O/O-hydrogen bonding interactions show exponential decay trend with the magnitude of bond path (R ij) values (R 2=0.993 for ρ (r) andR 2=0.938 for ∇2ρ (r)). However, there is a linear correlation betweenR ij values and the bond dissociation energies (D e) with the R 2 value of 0.975. For different HBs, these types of correlations have been found in previous work.42,43Among the above six interactions, four interactions (N2–H2C···O1, N1–H1C···O3, N2–H2A···O2W and N1–H1B···O1W) satisfy the conditions i.e. \(|\frac{V(r)}{G(r)}\)| < 1; H (r) > 0 and ∇2ρ (r) > 0) and these interactions are categorized as closed shell interactions and the remaining two interactions (N2–H2B ···O2 and N1–H1A···O5) have intermediate (\(|\frac{V(r)}{G(r)}\)| > 1;H (r) < 0 and ∇2ρ (r) > 0) values between closed and shared shell interactions.44 The Laplacian of the electron density and the total electronic energy density for these two interactions are shown in Fig. 6.