Topotactic desolvation and condensation reactions of 3D Zn 3 TiF 7 (H 2 O) 2 (taz) 3 ·S (S = 3H 2 O or C 2 H 5 OH)

Abstract : Crystals of two new 3D hybrid compounds, trans-Zn3TiF7(H2O)2(taz)3·3H2O and cis-Zn3TiF7(H2O)2(taz)3·C2H5OH, have been obtained by solvothermal synthesis ((taz)− = 1,2,4-triazolate C2H2N3 ligand). Their structures, determined from X-ray single crystal diffraction data in Cm and Pnma space groups, respectively, are based on Zn3N9(H2O)2F3 trimers linked by TiF6 octahedra that build trans- or cis-chains ∞[Zn3TiN9(H2O)2F7]. Water or ethanol in the structure cavities is released below 110 °C to give trans- or cis-Zn3TiF7(H2O)2(taz)3 and, on further heating, these intermediate phases dehydrate and lead to anhydrous trans- or cis-Zn3TiF7(taz)3. At 110 °C, the loss of ethanol concerns only ≈1/3 of the weight of cis-Zn3TiF7(H2O)2(taz)3·C2H5OH while the remaining part subsists up to 180 °C. This behaviour is attributed to a core–shell type configuration. Rehydration in humid air occurs at room temperature for the anhydrous cis-phase. All desolvated, dehydrated or rehydrated phase structures have been determined by X-ray powder diffraction and ab initio Rietveld refinements. All transformations from solvated or hydrated to anhydrous phases are realised without any symmetry change and the trans or cis connection of the TiF6 octahedra is maintained together with the overall features of the 3D networks. The final loss of water molecules induces a condensation reaction that implies the connection of the trimers by fluorine atoms; the structures of the anhydrous phases Zn3TiF7(taz)3 are then described by Zn3N9F4 trimers. 1H and 19F MAS NMR studies, coupled with DFT calculations of NMR parameters, confirm the water loss and support the strutural models while evidencing both the positional disorders, more likely of the organic parts, and the F motions within TiF6 octahedra.