Fig. 5: The energy diagram of the nitrate ion storage and the hydrogen-bond structure in the interlayer space.
From: Critical role of water structure around interlayer ions for ion storage in layered double hydroxides

The calculated binding energy of the ion-exchange system as a function of the interlayer distance of the optimised LDH structure a with highly charged LDHs [Mg0.66Al0.33(OH)2](NO3−)xB(Cl−)1−xB·mH2O and b with weakly charged LDHs: [Mg0.833Al0.166(OH)2](NO3−)xB(Cl−)1−xB·mH2O. The optimised LDH structures c of highly charged LDHs with xB = 0.0 (m = 0.42), xB = 0.125 (m = 0.25), and xB = 1.0 (m = 0.25), and d of weakly charged LDHs with xB = 0.0 (m = 0.42), xB = 0.25 (m = 0.25), and xB = 1.0 (m = 0.33). The three-dimensional and two-dimensional structured water along with chlorides emerges in the interlayer space of the optimised LDH structure e with highly charged LDHs and f with weakly charged LDHs, respectively. Here, the molecular arrangements are projected on the ab-plane of LDHs. In all crystal structures, orange, pale blue, red, white, green, and blue spheres represent magnesium, aluminium, oxygen, hydrogen, chlorine, and nitrogen atoms, respectively. To describe the interlayer hydrogen-bonding network, the interatomic bond lengths in the interlayer space (dotted lines) are set to 1.88 and 2.30 Å as the maximum H–O and H–Cl bond lengths, respectively50,51.