Sodium iodine(V) oxyfluoride, NaIO2F2

As an extension of a general structural study concerning fluorides and oxyfluorides of cations presenting a stereochemically active electronic lone pair, until now limited to tellurium(IV) phases, the previously unknown structure of NaIO(2)F(2) corresponds to a new structure type based on isolated IO(2)F(2)(-) polyhedra forming sheets separated by Na(+) layers. The sodium ion is octahedrally coordinated with 2/m site symmetry, while the I(V) atom has m2m symmetry with a stereochemically active lone electron pair. The O and F atoms (both with m symmetry) are bonded to the I(V) atoms in a fully ordered manner. A comparison with the structure of ferroelastic KIO(2)F(2) and with structures based on hexagonal close packing of anions, mainly rutile-type and FeTeO(3)F-type, reveals differences that are attributed to the smaller ionic radius of Na(+) and the ordering of the Na and I cations.