Dipotassium heptafluorotantalate(V), β-K2TaF7, at 509 K

Upon heating to 509 K, monoclinic α-K 2 TaF 7 ( P 2 1 / c ) transforms to orthorhombic β-K 2 TaF 7 ( Pnma ) which is composed of discrete K + cations and TaF 7 2− anions. In the anion, the Ta atom is sevenfold coordinated by F atoms, with the Ta—F distance varying from 1.88 (2) to 1.965 (19) Å. The two independent K + cations are surrounded by F atoms positioned within 2.740 (17)–2.979 (10) and 2.989 (17)–3.15 (5) Å. Ta, both K and one of the four F atoms are located on a mirror plane, Wyckoff position 4 c .