X-Ray powder structure and Rietveld refinement of γ-zirconium phosphate, Zr(PO4)(H2PO4)·2H2O

Abstract

A highly crystalline sample of γ-zirconium phosphate Zr(PO₄)(H₂PO₄)·2H₂O has been prepared by hydrothermal methods and its structure solved by X-ray powder diffractometry: monoclinic, space group P2₁, a= 5.3825(2), b= 6.6337(1), c= 12.4102(4)Å, β= 98.687(2)° and Z= 2. The final agreement factors are: R_wp= 0.105, R_p= 0.079 and R_F= 0.041. In the structure the metal atoms and one of the phosphate groups are located nearly in a plane. The octahedral co-ordination of the metal atom is completed by four oxygen atoms of the phosphate group and two oxygen atoms of the dihydrogenphosphate group. The remaining two oxygens of the dihydrogenphosphate group bind to protons and project into the interlayer space. These hydroxyl groups are hydrogen bonded to the water molecules. The water molecules reside in the pockets of these hydroxyl groups and are hydrogen bonded to each other to form a zigzag chain along the b axis.