{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.