The first oligomeric anions of fluoro-litho metallates with octahedra sandwich motive: Cs4K{[F3MIIIF3]Li[F 3MIIIF3]}, MIII = Ga, Fe

Article abstract of DOI:10.1002/zaac.19966220216

Colourless single crystals of Cs₄K{Li[Ga₂F₁₂]} (A) and Cs₄K{Li[Fe₂F₁₂]} (B) have been obtained by solid state reaction from intimate mixtures of the corresponding binary fluorides (Pt-tube, 750°C, 40 d). The trigonal unit cells with (A) a = 631,3(1) pm; c = 3059,9(6) pm and (B) a = 635,0(1) pm; c = 3089,2(7) pm, respectively (Z = 3, Guinier-Simon data, Cu-Kα₁), are confirmed by single crystal investigations. The compounds crystalize isostructural in the space group R3m (No. 166). The structures were determined using four-circle diffractometer data (Siemens AED 2) with (A) R = 2.95%, 3627 I_o and (B) R = 1.86%, 4179 I_o, respectively (SHELX-76), and are characterized by triplets of facesharing octahedra parallel [00.1] with the cation-sequence M^III-Li-M^III, six of which are connected by [KF₆]-octahedra via common corners and each triplet is surrounded by six different [KF₆]-octahedra. The structure is completed by Cs⁺ filling the cavities. The Madelung Part of Lattice Energy (MAPLE), Mean Fictive Ionic Radii (MEFIR) and Effective Coordination Numbers (ECoN) are calculated and compared. The classification as lithometallate could be verified by a new MAPLE concept. The Charge Distribution (CHARDI) was calculated and compared with the results according to 'bond length-bond strength'. Johann Ambrosius Barth 1996.