Cubic-Rhombohedral Structural Phase Transition in Na1.32Mn[Fe(CN)6]0.83·3.6H2O

We investigated the temperature dependence of the crystal structure for a cyano-bridged transition metal compound, Na 1.32 Mn[Fe(CN) 6 ] 0.83 ·3.6H 2 O, using a synchrotron radiation X-ray powder diffraction. We observed a cubic ( F m \bar3 m ; Z = 4) to rhombohedral ( R \bar3 m ; Z = 4) structural phase transition with decreasing temperature at T c = 280 K. In the cubic phase, we found that the guest Na ions are at the tetrahedral sites within the cyano-bridged transition metal cubes. We interpret the cubic-rhombohedral structural phase transition in terms of an order–disorder type transition of the Na + displacement mediated by the dipole–dipole interaction.