Metal (Ca, Ba, Sr, Pb) heptafluorotantalates(V): Synthesis, Raman spectra and crystal structures

MTaF7 (M = Ca, Sr, Ba, Pb) were prepared by the reaction of MF2 + Ta + F2 (Ca, Sr, Ba) or MF2 + TaF5 in anhydrous HF. CaTaF7 crystallizes in a monoclinic P21/a space group, a = 9.793(3) Å, b = 11.608(3) Å, c = 13.359(4) Å, β = 90.539(13)°, V = 1518.5(7) Å3. All Ta atoms possess distorted pentagonal-bipyramidal environment with Ta–F distances of 1.878(14)–2.044(13) Å. Three crystallographically independent Ca atoms have coordination number 8. Ca–F distances lie in the range of 2.239(16)–2.836(17) Å. Each Ca2+ and TaF72− moiety is bonded to 6 counter-ions. BaTaF7 crystallizes in a cubic system, space group Pa3¯,a = 9.9009(3)Å, V = 970.56(5) Å3. Coordination sphere around Ta atom is mono-capped trigonal prism with a Ta–F distance of 1.916(5)–2.004(5) Å. Two crystallographically independent barium atoms have different coordination numbers: for Ba1 C.N. is 12 with Ba1–F distances of 6 × 2.761(5) Å and 6 × 2.858(5) Å, for Ba2 C.N. is 14 with Ba2–F bond lengths 6 × 2.718(5), 2 × 2.814(8) and 6 × 3.236(5) Å. Ba2+ and TaF72− moieties are bonded to 8 neighbors. Isostructural PbTaF7 and SrTaF7 appear to be monoclinic, space group P21/m, a = 4.8657(11) Å, b = 7.2298(16) Å, c = 6.7370(16) Å, β = 93.932(13)°, V = 236.44(9) Å3 for PbTaF7, and a = 4.875(3) Å, b = 7.196(4) Å, c = 6.7218(13) Å, β = 94.265(10), V = 235.2(2) Å for SrTaF7. Tantalum coordination polyhedron may be described as a distorted mono-capped trigonal prism with the capping atom located on one of the rectangular faces with Ta–F distances of 1.868(3)–1.982(3) Å (PbTaF7) and 1.908(16)–2.019(12) Å (SrTaF7). Lead (or strontium) atoms are 9-coordinated and may be viewed as strongly distorted tri-capped trigonal prism, Pb–F 2.438(4)–2.669(3) Å, Sr–F 2.501(19)–2.860(19) Å. Each cation is connected to 8 anions.

Figure optionsDownload as PowerPoint slide