Crystal structure of synthetic zinc monophosphate Zn2(OH)PO4: A polymorph of tarbuttite.

The syntheses of zinc hydroxyl monophosphate Zn2(OH)PO4 were carried out under hydrothermal conditions of 573 K and 200 kg/cm2. The crystal data are: orthorhombic, P21212, a=8.099(1), =8.325(1) and c=5.966(1) Å. The structure was solved by three dimensional Patterson syntheses and refined by least squares methods to give a final residual index of R=0.042. There are four units of Zn2(OH)PO4 in a unit cell and three kinds of zinc atoms with different coordinations, where the first zinc atom is six-coordinated by four oxygen atoms and two hydroxyl groups, the second one is octahedrally coordinated by six oxygen atoms and the third one is five-coordinated by four oxygen atoms and one hydroxyl group forming distorted pyramids. The framework consists of infinite straight chains of Zn–O octahedra along c-axis, connected together by isolated PO4 tetrahedra and distorted Zn–O pyramids. This compound is a polymorph of tarbuttite.