F. Plet

Crystal structure and magnetic characterization of [C(NH2)3]3FeF6

Abstract The compound [C(NH 2 ) 3 ] 3 FeF 6 is prepared in closed bombs by digestion of FeF 3 and C(NH 2 ) 3 F in aqueous HF solutions. The material is cubic, space group Pa 3, a = 14.130(5) A, Z = 8. The crystal structure is determined from single-crystal diffraction intensity data refined to the conventional values of the indexes R = 0.0409 and R w = 0.0409 for the model containing the nonhydrogen atoms. All the hydrogen atoms are located by the final difference-Fourier map and lie near N atoms at distances in the range 1.02 to 1.09 A. The structure is characterized by two different sets of regular isolated (FeF 6 ) octahedra. Guanidinium cations are located on general 24-fold positions. The NH … F hydrogenbonding network is discussed. As expected, the compound is paramagnetic ( μ exp = 6.01 μ B , ϑ p = −5.6 K) and characterized by Mossbauer spectroscopy.

Croissance cristalline par voie hydrothermale en presence d'acide fluorhydrique dans les systèmes MF-AlF3 ET NH4F-FeF3

Abstract Single crystals of MIAlF4 (MI = K, Rb, Tl, NH4, Cs) and NH4Fe2F6 were grown by the hydrothermal method (at 300°C and 1600 bar) starting with AlF3 and FeF3 in an aqueous MIF (5M) solution of hydroflourhydric acid (5M). The compounds were anhydrous and did not undergo any hydrolysis phenomena. Optimal conditions of growth are described and the crystallographic data are given for all the phases.

K2AlF5 · H2O: Location of hydrogen atoms by X-ray diffraction and Raman spectroscopy study

Abstract The complete structural determination of K 2 AlF 5 · H 2 O is achieved by X-ray diffraction on a single crystal. As previously described, the cell is orthorhombic ( Cmcm , a = 9.200(3), b = 8.119(4), c = 7.486(3) A, Z = 4). The structure is essentially characterized by very slightly kinked chains of AlF 6 octahedra, sharing opposite corners, running in the [001] direction. Hydrogen atoms are located by difference Fourier synthesis on 8f positions; their introduction in the structural model improved the final results significantly ( R = 0.0383, R w = 0.0283). The OH … F hydrogen bonding system is discussed with the help of Raman spectroscopy.

Crystal structure and magnetic characterization of (NH4)2FeF5·H2O

Abstract The compound (NH 4 ) 2 FeF 5 ·H 2 O is prepared by hydrothermal synthesis in HF solutions. The material is orthorhombic, space group Pbcn , a = 10.491(4) A˚, b = 8.090(3) A˚, c = 7.997(3) A˚, Z = 4 . The crystal structure—isotypic with that of (NH 4 ) 2 AlF 5 ·H 2 O—is determined from single-crystal diffraction intensity data and refined to the conventional values of the indexes R = 0.0272 and R w = 0.0262 . The structure is characterized by isolated [FeF 5 (H 2 O)] 2− octahedra linked together by O H … F strong hydrogen bonds and forming zigzag chains running along 001. NH + 4 ions connect these chains by N H … F hydrogen bonds. As expected, the compound exhibits a paramagnetic behavior in the range 80–300 K and is not magnetically ordered at 4.2 K as shown by Mo¨ssbauer spectroscopy.

Proprietes d'echange ionique du pyrochlore TlNbO3 en presence de nitrates fondus ou solides

We have checked the ion-exchange properties of TlNbO3 in molten or solid nitrates. For Ag+ and Pb++, limited solid solutions of pyrochlore type are observed: T11−xAgxNbO3 (x < 0,75) and T11−xPbx2NbO3 (x ≤ 0,75). Localisation of Ag+ and Pb++ on the 16d positions of the space group Fd3m is confirmed by analysis of X-ray powder diffraction data. The thermal stability of the solid solutions is described and competition between pyrochlore and perovskite type is discussed.