Über Alkali-hexachlorochromate(III): Na3CrCl6

Alkali-hexachlorochromates(III): Na₃CrCl₆ X-ray investigations on single crystals yielded for Na₃CrCl₆ a trigonal structure: space group P3 1c; a = 682.0(3) pm; c = 1203.4(5) pm; Z = 2. In a hexagonal-close arrangement of Cl^? ions, 2/3 of the octahedral holes are occupied orderly by Na⁺ and Cr³⁺ ions. The Na compounds of V³⁺ and Mo³⁺ are isotypic. The chlorochromates with K and Rb are crystallizing with the K₃MoCl₆ structure according to X-ray photos of powders. The alkali metal ions habe the C.N. 8 or 11 related to the chloride ions. These compounds and elpasolithes A₂BCrCl₆ (A = Cs? K; B = Rb? Na) can be treated in the same way with the concept of tolerance factors as it is known for the chloro-perovskites AMCl₃. For all compounds the temperatures of phase transitions were determined by DTA. Some structures could be solved from high-temperature-Guinier-patterns, by comparing them with patterns of substances with known structures.