They also exhibit a significant shift to large angles compared to the simulated pattern. We focus on the (q(H2O)Na, q(Sr)) = (0.5, 1.0) conditions that provide the hydroxyapatite with the highest purity according to XRD. Wavelength-dispersive X-ray fluorescence (WDXRF) indicates Sr:Mn and Na:Mn ratios equal to 1.6 and 0.1, respectively, compared to 1.6 and 0 measured for hydroxyapatites obtained in other condition areas (Figure ). This suggests a strong default of Sr 2+ cations, in agreement with the Sr:Mn reagents ratio, and a significant amount of sodium for the apatite obtained at low q(H2O)Na. Rietveld refinement (Figure and Table ) indicates an a lattice parameter of 9.887 Å, considerably below the tabulated value (9.953 Å), while the c parameter does not show any significant deviation, so that the cell is smaller than the ideal structure. Fourier-transform infrared spectroscopy (FTIR) (Figure ), shows two bands at 752 and 798 cm -1 , which correspond to υ3 (Eu) and υ3 (A1u), vibration modes of MnO4 3-tetrahedra, respectively. The UVvisible spectrum (Figure ) shows a minimum of diffuse reflectance at 530 nm, consistent with the material's green color, characteristic of hydroxyapatites containing large amounts of Mn(V) tetrahedra. The Tauc plot analysis indicates a direct band gap of 2.7 eV, which was not reported before. Therefore, the material is still based on a Mn(V)-based hydroxyapatite structure. This structure provides a versatile framework for isovalent and aliovalent ion substitutions: while OH - in the structural channels can be substituted by F -in Sr5(MnO4)3OH, cationic substitution was also reported on Mn site, where Si 4+ replaces Mn 5+ . For the most studied calcium phosphate hydroxyapatite Ca5(PO4)3OH, substitution of the alkaline earth cation Ca 2+ has been widely investigated: alkali cations such as Na + can substitute Ca 2+ , which is accompanied by release of OH -from the channels along the c axis for charge compensation. This results in a decrease of the a lattice parameter. An identical trend is observed herein for the Mn(V) hydroxyapatite, hence we suggest Sr 2+ substitution by Na + and the release of OH -when the synthesis is performed at low q(H2O)Na. The resulting compound is a quinary phase NaxSr5-x(MnO4)3(OH)1-x, which agrees with the low Sr:Mn ratio measured by WDXRF. We therefore demonstrate that Mn(V) hydroxyapatites can be a versatile platform for cationic substitution and the synthesis of new materials.