APATITES, USEFUL TEMPLATES FOR ONE-DIMENSIONAL CHEMISTRY?

Peter Alberius Henning

Inorganic Chemistry, Stockholm University, 106 91 Stockholm, Sweden, peter@inorg.su.se

Keywords: Oxyapatite, Sulfoapatite, Iodo-oxyapatite, One-dimensional structures

The apatites and their structural chemistry continues to gather a lot of interest, mainly due to the biological significance of hydroxyapatite (Ca₅(PO₄)₃OH). One of the main structural-chemical questions concerning the calcium phosphate apatites today is the nature of carbonate-apatite (Ca₁₀(PO₄)₆CO₃). Carbonate ions are believed to be incorporated in biological apatite and influence mechanical as well as chemical properties of apatite in bone. The detailed crystallographic structure of carbonate-apatite remains unknown but there are a wide flora of apatites with other anions along the hexagonal channel that are structural-chemically interesting as well. Some of these newly prepared apatites will be presented and discussed.

This work is concentrated on an interesting structural chemical motif in the apatite structure, namely the anion X in Ca₅(PO₄)₃X, sitting in a "tunnel" parallel to the hexagonal c-axis. Deviations from the symmetry of fluoroapatite, P6₃/m, for different apatites are to a great extent determined by the position and nature of these anions. Hydroxyapatite is e.g.monoclinic due to alignment of the hydroxide ions within each column.

Previously the structures of calcium phosphate apatites with X=OH^-, F^-, Cl^-, Br^- have been reported. Recent results and structures of new apatites obtained in our group (oxyapatite, Ca₁₀(PO₄)₆O, P-6, iodo-oxyapatite, Ca₁₅(PO₄)₉IO, P6₃/m tripled along c, and sulfoapatite, Ca₁₀(PO₄)₆S, P-3) will be presented.

Other plausible calcium-phosphate apatites, synthesis routes and structures and the idea of the apatites being a suitable template for making "one-dimensional" structures will be discussed.