n(Mg)/n(Al)=3的水滑石层板结构及层间距的阴离子调控

Geometry of Hydrotalcite Slab with n(Mg)/n(Al)=3 and Regulation Effect of Interlayer Spacing with Anion

利用密度泛函理论(DFT)的B3PW91方法在Lanl2dz水平上研究了镁铝摩尔比为3的水滑石层板分子簇模型[Mg30Al7(OH)72]9+的几何构型,优化得到的结构参数和采用Reflex模块模拟得到的XRD图谱分别与实验观测结果相符,由此确定了水滑石层板沿第三维方向的有序堆积,该结构符合空间群R3m(166),其晶胞参数a=1.2552nm,c=2.3400nm.进一步构造了具有R3m空间群对称性的Mg-Al-CO32--LDH晶体结构模型,选取其中的簇模型,经优化得到了一种稳定构型,脱除结晶水的水滑石层间距为0.7260nm,键参数的变化表明碳酸根离子与层板间存在较强的超分子作用.

The slab microstructure of layered double hydroxide（LDH） with n（Mg）/n（Al） =3 is studied via density functional theory at the B3PWP91/Lanl2dz level. The optimized geometric parameters and the simulated XRD patterns of hydrotalcite are in agreement with experimental results. The structural simulations of hydrotalcite show that the host layers stack along the c-axis according to space group R3m, a = 1. 2552 nm, c = 2. 3400 nm. On the basis of the stacking muhilayer model, the carbonate anion is introduced into the interlayer space and one special cluster structure is obtained through optimization under the condition of keeping space group R3m. The computation results indicate that the interlayer spacing of hydrotalcite with removed crystal water is 0. 7260 nm. The changes of bond parameters of cluster suggest that there are strong supramolecular interactions between the slabs and anion.