Re‐evaluation of the X‐ray Crystal Structure of [Ta 4 F 20 ] and the Synthesis and Characterization of a Series of Mixed‐Metal Pentafluorides of Niobium and Tantalum

The direct fluorination of intimately mixed niobium and tantalum powders gives a range of mixed‐metal pentafluorides [Nb x Ta 4‐x F 20 ] (x = 1 2 , 2 3 , 3 4 ) as discreet species isostructural with tantalum pentafluoride (x = 0 1 ). The crystal structures of 1–4 are indistinguishable by X‐ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/m with a = 9.5462(13), b = 14.3578(19), c = 5.0174(7) Å, β = 97.086(2)°, Z = 2. The geometry about the tantalum atom is distorted octahedral with 2 short and 2 slightly longer Ta‐F terminal , and 2 Ta‐F bridging distances. The angles at the bridging fluorine atoms are 172.9(5)°.