Interlayer Structure and Dynamics of Cl-−LiAl2-Layered Double Hydroxide: 35Cl NMR Observations and Molecular Dynamics Modeling

Abstract

35Cl NMR experiments and molecular dynamics modeling provide significant new insight into the structure and dynamics of the interlayer species in the layered double hydroxide (LDH) LiAl2(OH)6Cl·nH2O. The LiAl2 LDHs have wide ranging potential applications as catalysts, as filtration and exchange materials, and in drug and gene-therapy delivery systems, and many of these applications depend on the behavior of interlayer species. Room-temperature MAS and static 35Cl NMR data indicate that the Cl- environments vary significantly with hydration state. The fully hydrated paste form has three types of Cl-: surface Cl- that yields a sharp solution-like peak at 0 ppm, interlayer Cl- that yields a resonance dominated by uniaxial chemical shift anisotropy (CSA), and interlayer Cl- that yields a structureless peak that is not fully narrowed by MAS. The relative abundance of the CSA dominated peak increases with decreasing hydration and is the only resonance observed for fully dried samples. For the dehydrated sampl...