Influence of Interlayer Water Content on Supermolecular Interaction of Copper-Iron Layered Double Hydroxides

Abstract

A periodic interaction model was proposed for the copper-iron layered double hydroxides, Cu3Fe-LDHs-yH2O (y=0-2). Based on density functional theory, the geometry of Cu3Fe-LDHs-yH2O was optimized using the CASTEP program. The distribution of NO - and H2O in the interlayer and the supermolecular interaction between host and guest was investigated by analyzing the geometric parameters, hydrogen-bonding, charge populations and stepwise hydration energy. Results indicated that when NO - and H2O were inserted into the layers of the Cu3Fe-LDHs, there was a strong supramolecular interaction between the host layer and the guest, including hydrogen-bonding and electrostatic interaction. Hydrogen-bonding was superior to the electrostatic interaction in the hydration process. The strength of hydrogen bonding was ordered as Layer-Anion (L-A) > Anion-Water (A-W) > Layer-Water (L-W) > Water- Water (W-W). In Cu3Fe-LDHs-yH2O, the interlayer distance decreased slightly and then increased significantly with an increase in the number of interlayer water molecules. The Cu―O octahedral forms were stretched gradually because of the increased Jahn-Teller effect of Cu 2+ . The absolute value of the hydration energy decreased gradually with an increase in the number of water molecules. This suggested that the hydration of Cu3Fe-LDHs reached a saturation state. The geometry of Cu3Fe-LDHs-1H2O is close to hexagonal where the metal distortion of the layer is weakest and the stability is strongest; the interlayer distance agrees the experimental value, therefore Cu3Fe-LDHs-1H2O is a stable configuration.