The crystal and molecular structure of potassium monofluoroxenate(VI), KXeO₃F

The crystal and molecular structure of potassium monofluoroxenate(VI), KXeO₃F, has been determined from three-dimensional X-ray data collected by counter methods. The material crystallizes in space group C_2V⁹-Pn2₁a of the orthorhombic system with four molecules in a cell of dimensions a = 7.374 (5), b = 6.811 (5), c = 8.185 (6) Å. The calculated density is 3.835 g cm^-3. Least-squares refinement of the structure has led to a final value of the conventional R factor (on F) of 0.054 for the 830 independent reflections having F² ≥ 3 σ(F²). The crystal structure consists of infinite chains, parallel to the b axis, of XeO₃ units linked by bridging fluorine atoms, with the potassium cations at nonbonded distances from the oxygen and fluorine atoms. The geometry of the XeO₃ moiety is very similar to that of Xe03 itself. The Xe-O distances are 1.75 (1), 1.76 (1), and 1.79 (1) Å, and the O-Xe-O bond angles are 97.8 (7), 100.5 (1.2), and 101.1 (9)°. The two independent Xe-F distances of 2.36 (1) and 2.48 (1) Å are considerably longer than the distances reported for nonbridging Xe-F bonds but are significantly shorter than the value of 3.5 Å predicted for nonbonded interactions between Xe and F. Thus, the description of this compound as a molecular addition complex of formula K ⁺F^- XeO₃ is incorrect, the correct formulation being nK⁺(XeO₃F^-)_n.