LiMnFeF 6 shows a dimorphism; the transition temperature α → β occurs at 560°C. The symmetry of the two phases is trigonal (space group P321, Z = 3) and the unit cell data are very close to each other: aα = 8.684(2), cα = 4.657(1), aβ = 8.723(2), cβ = 4.745(1) Å. The absolute structure of α-LiMnFeF 6 was determined from single-crystal X-ray data ( R = 0.020). This crystalline form exhibits a new kind of cationic order in the structural type Na 2SiF 6. The cationic distribution of β-LiMnFeF 6 was specified from X-ray and neutron powder diffraction data; this compound is isotypical with the LiMnGaF 6 structure. The different kinds of cationic distribution related to the Na 2SiF 6 type are discussed and a classification of the compounds Li(Na) MIIMIIIF 6 is given.