Crystal structures of NaBaCr 2F 9 and NaBaFe 2F 9: Structural correlations with other enneafluorides, particularly with KPbCr 2F 9
Abstract
NaBaCr 2F 9 and NaBaFe 2F 9 are monoclinic (SG {P2 1}/{n}, No. 14). Lattice constants are found to be a = 7.318(2) Å, b = 17.311(4) Å, c = 5.398(1) Å, β = 91.14°(3) for chromium, and a = 7.363(2) Å, b = 17.527(4) Å, c = 5.484(1) Å, β = 91.50°(5) for iron. The structures were solved from 507 and 1113 X-ray reflections, respectively, for the Cr and Fe compounds; the corresponding Rw values are 0.025 and 0.037. The network is built from tilted double cis chains of octahedra ( M2F 9) 3 n- n [ M = Cr, Fe], linked by Na + and Ba 2+ ions. The structures are compared to the previously described structures, particularly KPbCr 2F 9, whose symmetry and parameters are different. The difference is analyzed first in terms of tilted octahedra, but principally in terms of bond strengths and steric activity of the Pb 2+ lone pair. A mechanism is proposed for the transformation between the structures of NaBaCr 2F 9 and KPbCr 2F 9.
- Publication:
-
Journal of Solid State Chemistry France
- Pub Date:
- March 1985
- DOI:
- 10.1016/0022-4596(85)90178-1
- Bibcode:
- 1985JSSCh..56..288F