New Heptafluorozirconates and ‐hafnates A I B II Zr(Hf)F 7 (A I = Rb, Tl; B II = Ca, Cd) – Synthesis, Structures, and Structural Relationships

Four new ABZrF 7 heptafluorozirconates (A = Rb, Tl; B = Ca, Cd) and their homologous heptafluorohafnates, all colorless, orthorhombic Cmcm (n o 63), Z = 4, have been synthesized by heating stoichiometric mixtures of RbF or TlF, CaF 2 or CdF 2 and ZrF 4 (HfF 4 ) in sealed platinum tubes at temperature ranging from 550 °C (Tl) to 600 °C (Rb). The crystal structures of both RbCdZrF 7 and TlCdZrF 7 have been solved from single‐crystal X‐rays diffraction data. Rietveld refinements were performed from X‐rays powder patterns for RbCaZrF 7 and TlCaZrF 7 . In this series of heptafluorides, both B 2+ and Zr 4+ cations exhibit a pentagonal bipyramidal 7‐coordination. Their structural relationships with other heptafluorozirconates A I B II ZrF 7 as well as β‐KYb 2 F 7 are discussed. RbCaZrF 7 : a = 6.863(1) Å, b = 11.130(1) Å, c = 8.485(1) Å; TlCaZrF 7 : a = 6.868(1) Å, b = 11.165(1) Å, c = 8.486(1) Å; RbCdZrF 7 : a = 6.780(1) Å, b = 11.054(4) Å, c = 8.420(4) Å; TlCdZrF 7 : a = 6.784(3) Å, b = 11.099(2) Å, c = 8.424(9) Å.