A novel precipitation route has been developed for the synthesis of hydroxyapatite (HAP) nanostructures with the aid of various Schiff bases. To control size and shape of HAP nanostructures, the Schiff bases derived from acetylacetone (Hacac) and different diamines were used as chelating ligands for the in situ preparation of Ca2+ complexes. In this method, Ca(NO3)(2)center dot 4H(2)O and (NH4)(2)HPO4 were applied as calcium and phosphorus precursors, respectively. Moreover, the formation mechanisms of zero-dimension (0-D) and one-dimension (1-D) nanostructures of HAP were considered. When the Ca2+ ions could coordinate to the Schiff bases to form the [CaN2O2](2+) and [CaN4](2+) complexes, HAP nanoparticles were generated. On the other hand, nanobundles and nanorods of HAP were obtained by forming the [CaNO](2+) complexes in the reaction solution. This work is the first successful synthesis of pure HAP nanostructures in the presence of various Schiff bases. (C) 2014 Elsevier B.V. All rights reserved.