Get access

Nitrate-Intercalated Layered Double Hydroxides – Structure Model, Order, and Disorder



Layered double hydroxides with a high layer charge (+0.33 per empirical formula unit) intercalate nitrate ions with the molecular plane of the NO3 ion inclined at ca. 70° to the metal hydroxide layer, which results in a basal spacing of 8.8 Å. Three different N–O bond lengths are observed and yield Cs coordination symmetry. At lower charge (0.165 ≤ x ≤ 0.2), a basal spacing of 8.0 Å is observed, which indicates that the nitrate ion is intercalated with its molecular plane parallel to the metal hydroxide layer (coordination symmetry D3h) in a manner isostructural with carbonate-intercalated layered double hydroxides. Consequently, crystal chemical considerations predict the layer charge corresponding to the idealized composition of the nitrate-intercalated phase to be +0.165 per empirical formula unit. The [Mg–Al–NO3]0.165 phase is highly ordered with robust crystal growth along [001] and is stable to hydrothermal treatment, in contrast to the carbonate analogue of the same layer charge. Phases obtained with intermediate layer charge (+0.20 to 0.25 per empirical formula unit) exhibit structural disorder arising out of (i) planar faults and (ii) random interstratification of layers comprising nitrate ions in different orientations.

Get access to the full text of this article