The phase purity of a series of ZnAl4(OH)(12)SO4 center dot nH(2)O layered double hydroxides (ZnAl4-LDH) obtained from a reaction of bayerite (Al(OH)(3)) with an excess of zinc(II) sulfate under hydrothermal conditions was investigated as a function of the reaction temperature, the duration of the hydrothermal treatment, and the zinc(II) concentration. The product quality, i.e., crystalline impurities, Al impurities, and bulk Zn:Al ratio, were assessed by powder X-ray diffraction (PXRD), Al-27 MAS NMR, and elemental analysis. Structural characterization of a stoichiometric ZnA(l4)-LDH (120 degrees C, 9 days, and 2.8 M Zn(II)) showed a well-defined structure of the metal ion layer as evidenced by a single, well-defined Zn environment: i.e., no Zn substitution on the Al sites according to Zn k-edge EXAFS and PXRD. Furthermore, nearly all of the 12 different H-1 atoms in the -OH groups and 4 Al-27 resonances could be assigned using H-1, Al-27 NMR correlation experiments recorded with ultrafast MAS. The interlayer water content is variable on the basis of thermogravimetric analysis and changes in the H-1 MAS NMR spectra with temperature. A composition of ZnAl4(OH)(12)(SO4)center dot 2.6H(2)O was obtained from a combination of these techniques and confirmed that ZnAl4 -LDH is isostructural with the mineral nickelalumite (NiAl4(OH)(12)SO4 center dot 3H(2)O).