This compound undergoes a cubic to orthorhombic phase transition at ~156 K, driven by the Jahn-Teller distortion of the [Mn(OD₂)₆]³⁺ cation. A pronounced change in the magnetic properties of the compound ensues.

This work was carried out by Philip Louis William Tregenna-Piggott et al..

References:

• P. L. W. Tregenna-Piggott, H.-P. Andres, G. J. McIntyre, S. P. Best, C. C. Wilson, J. A. Cowan;
  "Aqua Ions. 2. Structural Manifestations of the Jahn-Teller Effect in the b-Alums"
  Inorg. Chem., 42, 1350-1365, (2003); doi:10.1021/ic0259639.