CRYSTAL-STRUCTURE AND MAGNETIC CHARACTERIZATION OF (NH4)2FEF5.H2O

The compound (NH//4)//2FeF//5 multiplied by (times) H//2O is prepared by hydrothermal synthesis in HF solutions. The material is orthorhombic, space group Pbcn, a equals 10. 491(4) Angstrom, b equals 8. 090(3) Angstrom, c equals 7. 997(3) Angstrom, Z equals 4. The crystal structure - isotypic with that of (NH//4)//2AlF//5 multiplied by (times) H//2O - is determined from single-crystal diffraction intensity data and refined to the conventional values of the indexes R equals 0. 0272 and R//w equals 0. 0262. The structure is characterized by isolated left bracket FeF//5(H//2O) right bracket **2** minus octahedra linked together by O-H . . . F strong hydrogen bonds and forming zigzag chains running along 001. NH** plus //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 Moessbauer spectroscopy.