Crystal structures of substituted apatites with general formula Ca10-xMx(PO4)6(OH1-δ)2-xOx, where M=La, Bi, 0≤x<2, were refined using high-resolution X-ray powder diffraction patterns. Individual positions for Ca2+ and M3+-ions localized near Ca2-site were determined. The M3+-ion was found shifted toward the hexagonal channel center with respect to the Ca2+-ion, forming very short bond with the intrachannel O2-, while leaving considerably longer distances to other oxygen atoms, which suggested the existence of a MO+ ion. Distinct bands of stretching M-O modes were observed in the Raman and FT-IR spectra of the compounds. The bond lengths for BiO+ and LaO+ were estimated to be 2.05(1) and 2.09(1) Å correspondingly. The latter was almost 0.3 Å lower than the shortest La-O bond in La2O3. The realization of such a strong lanthanide-oxygen bond in a crystal lattice could provide a very high axial ligand field and might be implemented to develop high-energy-barrier single-molecule magnets as well as to tune properties of lanthanide-based luminophores.
- Bond length
- Structure elucidation