Layer double hydroxides ( (\mathrm{LDHs}) ) have been obtained by chimie douce reactions from the (\mathrm{NaNi}{1-y} \mathrm{Co}{y} \mathrm{O}{2}) cobalt substituted sodium nickelate ((0 \leq y \leq 0.5)). These materials exhibit the general formula (\mathrm{Ni}{1-y} \mathrm{Co}{y}(\mathrm{OH}){2} X_{y i n}, z \mathrm{H}{2} \mathrm{O}, X^{n-}=\mathrm{CO}{3}^{2-}, \mathrm{NO}{3}^{-}, \mathrm{Cl}^{-}, \mathrm{OH}^{-}, \mathrm{SO}{4}^{2-} \ldots) The (X^{n-}) anions and the water molecules are inserted between the hydroxide slabs. The (\mathrm{Ni}{1-y} \mathrm{Co}{y} \mathrm{O}_{2}) slabs are built up during the high temperature preparation of the sodium nickelate, while the anions are inserted later on during the chimie douce reaction. It follows that a wider range of materials can be obtained than in the case of classical precipitation reactions. Moreover, the materials are well crystallized. The LDHs have been characterized by X-ray diffraction and by IR spectroscopy. The observed anion selectivity is discussed on the basis of electrostatic interactions and steric effects. (1993 Academic Press, Inc.