hide
Free keywords:
niobium oxide fluoride; tantalum oxide fluoride; crystal structure; IR spectroscopy; NMR spectroscopy
Abstract:
Powder samples of NbOF3 und TaOF3 were prepared by heating
mixtures of NbO2F and NbF5 or TaO2F and TaF5, respectively, in
the corresponding stoichiometric ratio in platinum crucibles
under argon atmosphere (180-220degreesC). Both oxide fluorides
are coulourless with a slight greyish tinge. They are sensitive
to moisture and decompose in air at room temperature within
hours. Both, NbOF3 and TaOF3 crystallize as a variant of the
SnF4 type structure, space group 14/mmm. The structures have
been refined from X-ray powder diffraction data using the
Rietveld method (a = 3.9675(1) Angstrom, c = 8.4033(1)
Angstrom, R-B = 3.60%, R-p = 4.58% for NbOF3 and a = 3.9448(1)
Angstrom, c = 8.4860(1) Angstrom, R-a = 2.07%, R-p = 2.44% for
TaOF3). Characteristic building units are sheets of corner
sharing MX6 octahedra which are stacked via van der Waals
interactions to a three dimensional framework. The occupancy of
the two crystallographic sites for the anions by O and F is
discussed on the basis of structure refinements, bond order
summations, IR and NMR data and calculations of the Madelung
parts of the lattice energy.
