Bildung des „superoktaedrischen”︁ Heteropolyanions [Ni(TaF6)6]4− bei der Oxidation von Tantal mit Ammoniumfluorid an der Monel-Wand

Formation of the “Superoctahedral” Heteropolyanion [Ni(TaF₆)₆]^4? through Oxidation of Tantalum with Ammonium Fluoride at the Monel-Container Wall A few single crystals of (NH₄)₄[Ni(TaF₆)₆] are obtained besides (NH₄)[TaF₆] as the main product of the reaction of (NH₄)F with tantalum powder in an He-are-welded Monel metal container at 400°C. The crystal structure (trigonal, R-3c (Nr. 167), Z = 6, a = 1723,0(2); c = 2166,6(2) pm; R1 = 0,0303, _WR2 = 0,0609) contains the superoctahedral heteropolyanion [Ni(TaF₆)₆]^4? and (NH₄)⁺ ions; it may be recognized as a derivative structure of the K₄CdCl₆ type according to (NH₄)₄[Ni(TaF₆)₆]?K₄[Cd(Cl)₆].