The chlorides Na3MCl6 (M  Eu-Lu, Y, Sc): Synthesis, crystal structures, and thermal behaviour

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Abstract
Single crystals of Na3ErCl6 were obtained via the metallothermic reduction of ErCl3 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 P21/n. Two applicable synthetic routes to pure powder samples of the chlorides Na3MCl6 (M  EuLu, Y, Sc) are described. With M  DyLu, Y, Sc, these are isotypic with Na3ErCl6 while those with M  Eu, Gd, Tb adopt a „stuffed”︁ LiSbF6‐type structure. The dimorphism of Na3GdCl6 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 LiSbF6‐type Na3GdCl6‐I to the cryolite‐type Na3GdCl6‐II occurs exhibiting a 3.71% negative molar volume discontinuity.