Structures and Properties of NbOF₃ and TaOF₃ — With a Remark to the O/F Ordering in the SnF₄ Type Structure.

Abstract

The title compounds are prepared by reacting stoichiometric mixtures of NbO 2 F and NbF 5 or TaO 2 F and TaF 5 , resp., at 180-220°C (Pt crucibles, argon, 12-24 h). The isotypic compounds crystallize in space group I4/mmm with Z = 10 (variant of the SnF 4 type). The structure consists of layers of corner-sharing M(O,F) 6 octahedra which are stacked to a three-dimensional framework via van der Waals interactions. The occupancy of the two crystallographically different anion sites by O and F is discussed on the basis of the structure refinements, bond order summations, IR and NMR data, and calculations of the Madelung parts of the lattice energy. -(KOEHLER*, J.; SIMON, A.; VAN WUELLEN, L.; CORDIER, S.; ROISNEL, T.; POULAIN, M.; SOMER, M.; Z.

Preparation-Dependent Composition and O/F Ordering in NbO2F and TaO2F

“…Lastly, the 19 F δ iso value of the main line of AQ_NbO 2 F is in agreement with the previously reported value (−52 ppm) from the 19 F solid-state NMR study of the NbOF 3 sample containing NbO 2 F as byproduct. 15 In light of the above assignments and trends for 19 F δ iso values, the assignments of Koḧler et al 15 for NbOF 3 and TaOF 3 (that is, the 19 F NMR lines with the lowest δ iso (−10.4 and −51.5 ppm) values to the terminal F and the 19 F NMR lines with the highest δ iso (196.3 and 124.2 ppm) values to the bridging F) have to be reversed.…”

“…15,18−27 In the present cases where metal vacancies are expected, 19 F solidstate NMR should allow identifying and quantifying the various F environments since the 19 F isotropic chemical shift (δ iso ) value depends on the coordination number of F as shown, for example, in NbF 5 and TaF 5 , 28 and as applied on titanium oxyhydroxyfluorides with cationic vacancies. 29−33 The 19 F solidstate NMR study of NbOF 3 and TaOF 3 samples containing NbO 2 F and TaO 2 F as byproduct 15 will be discussed below. Moreover, solid-state 93 Nb NMR is one of the most promising techniques to study the local environment of niobium in solids, particularly when diffraction methods may fail due to disorder.…”

Facile synthetic route to transition metal oxyfluorides via reactions between metal oxides and PTFE

“…Several niobium oxyfluorides are known to date: a homologous series Nb n O 2n-1 F n+2 (n = 1 [12], 3 [13], and ∞ [14,15]), Nb 3 O 7 F, and Nb 5 O 12 F [16]. Moreover, a new compound Nb 2 O 2 F 3 [17] was discovered in 2015.…”

“…Tantalum and niobium are the same group V elements. Tantalum oxyfluorides, however, have been less investigated compared to Nb ones, and only three compounds Ta 3 O 7 F [20], TaO 2 F [21], and TaOF 3 [12] have been reported. We successfully synthesized Ta 3 O 7 F and TaO 2 F by using the PTFE fluorination method.…”