Crystal structures of biocompatible Mg-, Zn-, and Co-whitlockites synthesized via one-step hydrothermal reaction

Abstract Large-scale single crystals of Ca9Mg(PO4)6(PO3OH), Ca9Zn(PO4)6(PO3OH), and Ca9Co(PO4)6(PO3OH) were synthesized using hydrothermal technique, and turned out to be similar to natural bone whitlockite. The hexagonal single crystals about 1 mm with high-quality were obtained with this method for the first time. The crystals were of sufficiently good quality for the precision X-ray structural investigation. The compounds crystallize in usual for this structural type trigonal space group R3c. Presence of hydrogen atom in the structure was confirmed by means of infra-red (IR) spectroscopy, differential scanning calorimetry (DSC) and differential thermogravimetry (DTG) methods. Based on the analysis of the local bond valence sum (BVS), a conclusion on the localization of H atoms was made. The formation of O–H groups and hydrogen bonds H⋯O in vicinity of PO4 tetrahedra was shown and similar to bone whitlockite. This research provides new data on possibility of using hydrothermal technique for obtaining doped bone whitlockites. Hydrogen-containing doped whitlockites can combine bioactive properties and improve biocompatibility due to similarity to natural bond. New structural data are useful for finding the ways to better biocompatibility of whitlockite-based materials.