The chlorides Na 3 MCl 6 (M  EuLu, Y, Sc): Synthesis, crystal structures, and thermal behaviour

Single crystals of Na 3 ErCl 6 were obtained via the metallothermic reduction of ErCl 3 with Na. The crystal structure is that of the mineral cryolite with a = 684.54(4), b = 725.18(4), c = 1012.39(6) pm, β = 90.768(5)°, Z = 2, space group P2 1 /n. Two applicable synthetic routes to pure powder samples of the chlorides Na 3 MCl 6 (M EuLu, Y, Sc) are described. With M DyLu, Y, Sc, these are isotypic with Na 3 ErCl 6 while those with M Eu, Gd, Tb adopt a „stuffed” LiSbF 6 ‐type structure. The dimorphism of Na 3 GdCl 6 and dependence of the lattice constants and the molar volume upon temperature has been investigated: At 205°C, a first‐order phase transition from the stuffed LiSbF 6 ‐type Na 3 GdCl 6 ‐I to the cryolite‐type Na 3 GdCl 6 ‐II occurs exhibiting a 3.71% negative molar volume discontinuity.