Template-directed synthesis of hydroxyapatite from a lamellar phosphonate precursor

The thermal decomposition of a lamellar hydroxyapatite precursor containing crystalline complexes leads to the formation of an apatite product with bonelike morphology. Solid-state ¹³C and ³¹P nuclear magnetic resonance, infrared, and Raman vibrational spectroscopic data show that the hydroxyapatite precursor contains acetyl hydrogen phosphonates and at least two types of acetate species. Phosphoryl and carboxyl oxygens of the phosphonate group are chelated to the calcium ion. The oxygens of the other acetate groups are involved in either monodentate bonding or chelation. The most important consequence of the morphology of the intermediate is the formation of apatite retaining the precursor morphology. The process emulates the formation of biogenic apatites, where the formation of an intermediate phase with platelike morphology serves as a template for apatite formation with a morphology similar to that of the precursor.