New iron-substituted nickel hydroxides have been prepared by chimie douce reactions from the (\mathrm{NaNi}{1-x} \mathrm{Fe}{x} \mathrm{O}{2}) precursor phases. Oxidizing hydrolysis of these materials leads to (\gamma)-oxyhydroxides which are then easily reduced to hydroxides. A crystal chemical study of the three material classes has been performed. The precursor phases crystallize in the rhombohedral system for (x \geq 0.2), while the lower iron concentrations lead to a monoclinic distortion due to the Jahn-Teller effect of (\mathrm{Ni}^{\mathrm{II}}) ions. This distortion is not observed in the case of the (\gamma) phases. For (x \geq 0.2), the hydroxides also crystallize in the rhombohedral system, whereas for smaller iron concentrations, interstratified-type structures similar to those commonly found among the layered double hydroxide minerals family are obtained. Chemical analysis and magnetic property study have shown the presence of ((1-x) \mathrm{Ni}^{2+}) and (x \mathrm{Fe}^{3+}) ions within the slab. Anions (mainly (\mathrm{CO}{3}^{2-}) ions) are inserted into the intersheet space in order to compensate the excess positive charge due to (\mathrm{Fe}^{3+}) ions. 1993 Academic Press, Inc.