A new refinement of the crystal structure of MnAlF5 : new structural correlations with MnCrF5 and Cr2F5 using orthogonal subcell twinning

Abstract A new refinement of the crystal structure of MnAlF 5 , needed for further powder neutron diffraction studies, shows that it is centric (S.G. Cmcm, a = 3.5837(4) A, b = 9.854(1) A, c = 9.537(1) A, Z = 4). The structure was refined from 720 independent reflections ( R 0.023, R w = 0.022). Its crystal chemistry is basically the same as previously described, but a new comparison with MnCrF 5 and Cr 2 F 5 is proposed. It first shows that the latter two structures represent two different monoclinic distortions of the same structural type, despite large differences in their lattice parameters. This leads to a description of MnAlF 5 as a twinning of two subcells of this structural type and to an introduction of the concept of subcell orthogonal twinning.