Triclinic apatites

Tom Baikie; Patrick H.J. Mercier; Margaret M. Elcombe; Jean Y. Kim; Yvon Le Page; Lyndon D. Mitchell; T. J. White; Pamela S. Whitfield

doi:10.1107/S0108768106053316

Triclinic apatites

Tom Baikie^*, Patrick H.J. Mercier, Margaret M. Elcombe, Jean Y. Kim, Yvon Le Page, Lyndon D. Mitchell, T. J. White, Pamela S. Whitfield

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

56 Citations (Scopus)

Abstract

Apatites commonly adopt P63/m hexagonal symmetry. More rarely, monoclinic chemical analogues have been recognized, including the biologically significant hydroxyapatite, Ca10(PO4)6(OH)2, but the driving force towards lower symmetry has not been systematically examined. A combination of diffraction observations and ab initio calculations for Ca10(AsO4)6F2 and Ca10(VO4)6F2 show these materials are triclinic apatites in which the AsO4 and VO4 tetrahedra tilt to relieve stress at the metal and metalloid sites to yield reasonable bond-valence sums. An analysis of the triclinic non-stoichiometric apatites La10 - x (GeO4)6O3 - 1.5x and Ca10(PO4)6(OH)2 - x O x/2 confirms this scheme of tetrahedral rotations, while Cd10(PO4)6F2 and Ca10(CrO4)6F2 are predicted to be isostructural. These distortions are in contrast to the better known P1121/b monoclinic dimorphs of chloroapatite and hydroxyapatite, where the impetus for symmetry reduction is ordered anion (OH^- and Cl^-) displacements which are necessary to obtain acceptable bond lengths. These results are important for designing apatites with specific structural and crystal-chemical characteristics.

Original language	English
Pages (from-to)	251-256
Number of pages	6
Journal	Acta Crystallographica Section B: Structural Science
Volume	63
Issue number	2
DOIs	https://doi.org/10.1107/S0108768106053316
Publication status	Published - Mar 16 2007
Externally published	Yes

ASJC Scopus Subject Areas

General Biochemistry,Genetics and Molecular Biology

Keywords

Apatites
Bond-valence sum
Neutron powder diffraction
Symmetry

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10.1107/S0108768106053316

Cite this

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title = "Triclinic apatites",

abstract = "Apatites commonly adopt P63/m hexagonal symmetry. More rarely, monoclinic chemical analogues have been recognized, including the biologically significant hydroxyapatite, Ca10(PO4)6(OH)2, but the driving force towards lower symmetry has not been systematically examined. A combination of diffraction observations and ab initio calculations for Ca10(AsO4)6F2 and Ca10(VO4)6F2 show these materials are triclinic apatites in which the AsO4 and VO4 tetrahedra tilt to relieve stress at the metal and metalloid sites to yield reasonable bond-valence sums. An analysis of the triclinic non-stoichiometric apatites La10 - x (GeO4)6O3 - 1.5x and Ca10(PO4)6(OH)2 - x O x/2 confirms this scheme of tetrahedral rotations, while Cd10(PO4)6F2 and Ca10(CrO4)6F2 are predicted to be isostructural. These distortions are in contrast to the better known P1121/b monoclinic dimorphs of chloroapatite and hydroxyapatite, where the impetus for symmetry reduction is ordered anion (OH- and Cl-) displacements which are necessary to obtain acceptable bond lengths. These results are important for designing apatites with specific structural and crystal-chemical characteristics.",

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author = "Tom Baikie and Mercier, {Patrick H.J.} and Elcombe, {Margaret M.} and Kim, {Jean Y.} and {Le Page}, Yvon and Mitchell, {Lyndon D.} and White, {T. J.} and Whitfield, {Pamela S.}",

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AU - Baikie, Tom

AU - Mercier, Patrick H.J.

AU - Elcombe, Margaret M.

AU - Kim, Jean Y.

AU - Le Page, Yvon

AU - Mitchell, Lyndon D.

AU - White, T. J.

AU - Whitfield, Pamela S.

PY - 2007/3/16

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N2 - Apatites commonly adopt P63/m hexagonal symmetry. More rarely, monoclinic chemical analogues have been recognized, including the biologically significant hydroxyapatite, Ca10(PO4)6(OH)2, but the driving force towards lower symmetry has not been systematically examined. A combination of diffraction observations and ab initio calculations for Ca10(AsO4)6F2 and Ca10(VO4)6F2 show these materials are triclinic apatites in which the AsO4 and VO4 tetrahedra tilt to relieve stress at the metal and metalloid sites to yield reasonable bond-valence sums. An analysis of the triclinic non-stoichiometric apatites La10 - x (GeO4)6O3 - 1.5x and Ca10(PO4)6(OH)2 - x O x/2 confirms this scheme of tetrahedral rotations, while Cd10(PO4)6F2 and Ca10(CrO4)6F2 are predicted to be isostructural. These distortions are in contrast to the better known P1121/b monoclinic dimorphs of chloroapatite and hydroxyapatite, where the impetus for symmetry reduction is ordered anion (OH- and Cl-) displacements which are necessary to obtain acceptable bond lengths. These results are important for designing apatites with specific structural and crystal-chemical characteristics.

AB - Apatites commonly adopt P63/m hexagonal symmetry. More rarely, monoclinic chemical analogues have been recognized, including the biologically significant hydroxyapatite, Ca10(PO4)6(OH)2, but the driving force towards lower symmetry has not been systematically examined. A combination of diffraction observations and ab initio calculations for Ca10(AsO4)6F2 and Ca10(VO4)6F2 show these materials are triclinic apatites in which the AsO4 and VO4 tetrahedra tilt to relieve stress at the metal and metalloid sites to yield reasonable bond-valence sums. An analysis of the triclinic non-stoichiometric apatites La10 - x (GeO4)6O3 - 1.5x and Ca10(PO4)6(OH)2 - x O x/2 confirms this scheme of tetrahedral rotations, while Cd10(PO4)6F2 and Ca10(CrO4)6F2 are predicted to be isostructural. These distortions are in contrast to the better known P1121/b monoclinic dimorphs of chloroapatite and hydroxyapatite, where the impetus for symmetry reduction is ordered anion (OH- and Cl-) displacements which are necessary to obtain acceptable bond lengths. These results are important for designing apatites with specific structural and crystal-chemical characteristics.

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Triclinic apatites

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Keywords

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