Quantum chemistry and molecular mechanics studies of the lamella structure of hydrotalcite with Mg/Al ratio of 3

The layered structures of hydrotalcites with Mg/Al ratio of 3 are studied by using quantum chemistry and molecular mechanics methods. The coordination structure and morphology of hydrotalcite are described by a series of molecular cluster models of lamellae. The geometries of cluster models of lamellae are fully optimized at the level of semiempirical molecular orbital methods and density functional theory, respectively. The computing results show that the lamellae of hydrotalcite with Mg/Al ratio of 3 have a special Mg-Al atomic arrangement and the stable structures of cluster models have hexagonal shapes corresponding to the experimental morphology of lamellae of hydrotalcites. The Mg/Al ratio of lamellae is found to be an alterable number variable with the size of laniella, and the ratio 3 is an utmost when lamella diameter becomes large enough. The highest occupied molecular orbitals on oxygen atom at the edge of the lamellae are easy to attract metal cations and the lowest unoccupied molecular orbitals near the Al3+ ions are fit to accept intercalated anions. (c) 2007 Elsevier Ltd. All rights reserved.