Acta Cryst. (2003). E59, i125-i128  [ doi:10.1107/S1600536803017537 ]

Mg-rich wolfeite, (Fe^II,Mg)₂(PO₄)(OH): structure refinement and Raman spectroscopic data

U. Kolitsch

Abstract: Mg-rich wolfeite [diiron(II) hydroxide phosphate], (Fe^II,Mg)₂(PO₄)(OH), from the Big Fish River area, Yukon Territory, Canada, is isotypic with its Mn^II-dominant analogue triploidite. The framework structure contains edge- and corner-sharing, distorted MO₄(OH) and MO₄(OH)₂ (M = Fe^II or Fe^II,Mg) polyhedra linked by fairly regular PO₄ tetrahedra. All atoms are on general positions. Four of the eight independent Fe sites contain between 9 and 25% Mg substituting for Fe. Two of these four sites show distorted trigonal-bipyramidal coordination, whereas the remaining two sites show distorted octahedral coordination. The average (Fe^II,Mg)-O bond length decreases with increasing Mg content. Average P-O distances range between 1.538 and 1.543  Å. The hydrogen bonds are all strongly bent and weak, with OO distances > 2.73  Å, an observation confirmed by single-crystal Raman spectroscopic data which show five bands due to O-H stretching vibrations between 3478 and 3557  cm^-1.

Online 15 August 2003

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