KHfF₅: a new representative in the M^IM^IVF₅ family

We report the preparation and crystal structure of potassium hafnium pentafluoride, KHfF₅, obtained by the hydrothermal technique. The compound crystallizes in the orthorhombic noncentrosymmetric space group P2₁2₁2₁, with the unit-cell parameters a = 6.2843 (3), b = 7.8063 (3) and c = 15.8286 (7) Å. Hf atoms are coordinated by eight F atoms, forming square antiprismatic polyhedra. Bonding in pairs, HfF₈ antiprisms are interconnected via common F-atom edges and form a double chain of hafnium polyhedra. A comparison of the structure of KHfF₅ with other complex fluorides of alkali metals and hafnium, zirconium or terbium(IV) revealed that this compound has no isostructural analogue among the known phases of general composition M^IM^IVF_5.