2D zirconium fluorides: Synthesis, structure and NMR spectroscopy

Two new zirconium (IV) fluorides, [H2dap]·(Zr2F10)·H2O (I) and [Hmeam]2·(Zr2F10)·H2O (II), are synthesized and characterized by X-ray diffraction, thermal techniques and NMR spectroscopy. I is triclinic (P1¯) with a = 6.805 (1) Å, b = 8.361(1) Å, and c = 11.853 (2) Å, α = 94.54(1)°, β = 105.44(1)°, γ = 108.75(1)°. II is monoclinic (C2/m) with a = 10.340(6) Å, b = 6.624(4) Å, c = 8.758(6) Å and β = 110.57(3)°. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R/Rw reliability factors 0.041/0.113 for I and 0.057/0.177 for II. The structures are built up from ZrF7 and ZrF8 units in I and only ZrF8 units in II. The polyhedra share common edges in order to form two different ZrF5 layers that are also found in [H2C2H10N2]·(Zr2F10)·H2O and (H3O)2·(Zr2F10)·H2O. On heating at 145 °C, [H2dap]·(Zr2F10)·H2O decomposes to give the anhydrous form [H2dap]·(Zr2F10) that undergoes two successive phase transformations at 220 °C and 290 °C. 19F NMR spectroscopy confirms the structural features of [H2dap]·(Zr2F10)·H2O (I): two sets of three lines with a relative intensity 1:2:2 are attributed to five bridging fluorine atoms and to five nonbridging fluorine atoms. This spectroscopy demonstrates that a noticeable substitution of F− anions by hydroxyl OH− groups is excluded, together with the eventual substitution of H2O by HF molecules.

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