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, Na1.32Mn[Fe(CN)(6)](0.83)center dot 3.6H(2)O, using a synchrotron radiation X-ray powder diffraction. We observed a cubic (Fm (3) over barm; Z = 4) to rhombohedral (R (3) over barm; 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.