Hydrogen bond network of the layered phosphates γ-Zr(H2PO4)(PO4)⋅2H2O and γ-Hf(H2PO4)(PO4)⋅2H2O determined by neutron powder diffraction

Abstract

Abstract The hydrogen atom positions of the layered phosphates Zr(PO4)(H2PO4)⋅2H2O (γ-ZrP) and Hf(PO4)(H2PO4)⋅2H2O (γ-HfP) have been determined from neutron powder diffraction data and the complete crystal structures have been refined by the Rietveld method. The compounds crystallize in the monoclinic space group P21. The final agreement factors are: R wp = 1.47, R exp = 0.91 for γ-ZrP and R wp = 1.73, R exp = 1.43 for γ-HfP. The two compounds are isostructural and posses a dense hydrogen-bonding network. They are formed by layers consisting of two planes of metallic atoms joined by phosphate and dihydrogenphosphate groups. The interlayer space form channels where each water molecule accepts and donates an hydrogen bond to another water molecule forming a zig-zag chain. Additionally each water molecule acts as acceptor and donor in two hydrogen bonds with oxygen atoms of the same layer. Consecutive layers are, in this way, indirectly held together by hydrogen bonds through the water molecules.