Syntheses and superstructures of (Cd, M)₅(PO₄)₃OH (M=Mn, Fe, Co, Ni, Cu, Hg)

Abstract

Divalent ions of the first series transition elements and Hg were introduced into a cadmium hydroxyapatite Cd₅(PO₄)₃OH by replacing a part of Cd²⁺, and the effects on the crystal growths and the structural changes were studied. Cd²⁺ can be exchanged with Mn²⁺ up to about 30 mol %, with Ni²⁺ or Hg²⁺ up to about 10 mol %, and with a little amount of Fe²⁺ or Cu²⁺. It was found that Cd₅(PO₄)₃OH forms a superstructure when it contains a small amount of Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ or Hg²⁺ ion. Infrared spectra of Cd₅(PO₄)₃OH containing these ions show some new bands in addition to those of Cd₅(PO₄)₃OH. The average structures of the crystals containing a small amount of Hg²⁺ and Ni²⁺, and the superstructure of the crystal containing Mn²⁺ were refined with the full-matrix least-squares method, although the amounts and sites of the substituting ions could not be determined except for the crystals containing Hg²⁺. The superstructure belongs to P6₃ (a=16.1990(3), c=6.6485(1)Å and Z=6) and has more distorted PO₄ tetrahedra than the structure of pure Cd₅(PO₄)₃OH.