层间水分子含量对铜铁水滑石超分子作用力的影响

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

构建铜铁水滑石[Cu3Fe-LDHs-yH2O (y=0-2)] 周期性计算模型, 采用密度泛函理论 (DFT), 选取CASTEP程序模块, 对体系进行几何全优化. 从结构参数、氢键、Mulliken电荷布居、逐级水合能等角度研究了层间NO3-和H2O的分布形态及其与水滑石(LDHs)层板的超分子作用, 探究了水分子数目对体系姜-泰勒效应的影响. 结果表明: Cu3Fe-LDHs-yH2O主客体间存在着较强的超分子作用力, 主要包括氢键和静电作用, 其中氢键作用在水合过程中起主导作用, 氢键强度的顺序是层板-阴离子(L-A)型>阴离子-水(A-W)型>层板-水(L-W)型>水-水(W-W)型; 随着层间水分子数的增加, 层间距先略微降低后显著升高, Cu3Fe-LDHs体系的 Cu―O八面体被逐渐拉长, 层板Cu2+的姜-泰勒畸变程度逐渐增大, 体系的逐级水合能绝对值逐渐降低, 说明Cu3Fe-LDHs的水合程度不会无限增加, 而是具有一个饱和值. Cu3Fe-LDHs-1H2O构型接近理想六方晶胞, 层板金属畸变程度最小, 稳定性最高, 层间距与实验值较吻合, 推测其为实验上合成的Cu3Fe-LDHs较稳定的构型.

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 NO3- 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 showed that when NO3- and H2O were inserted into the layers of Cu3Fe-LDHs, there was 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 Layer-Anion（L-A） type hydrogen bonding〉Anion-Water（A-W） type hydrogen bonding〉L-A type hydrogen bonding〉Layer-Water（L-W） hydrogen bonding〉 Water-Water（W-W） type hydrogen bonding. 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 the Jahn-Teller effect of Cu2＋ increased. The absolute value for the hydration energy decreased gradually with an increase in the number of water molecules. This suggested that the hydration of Cu3Fe-LDHs reached a definite saturation state. The geometry parameters of Cu3Fe-LDHs-1H2O is close to the ideal hexagonal, the metal distortion of layer is the weakest and the stability is the strongest, interlayer distance matchs with the experimental value, so the Cu3Fe-LDHs-1H2O is a stable configuration.