The structure, phase transition and molecular dynamics of [C(NH2)3]3[Sb2Br9]

The crystal structures of [C(NH2)3]3[Sb2Br9] (Gu3Sb2Br9) at 300 K and of [C(NH2)3]3[Sb2Cl9] (Gu3Sb2Cl9) at 90 and 300 K are determined. The compounds crystallize in the monoclinic space group: C 2/c. The structure is composed of Sb2X93− (X = Cl, Br) ions, which form two-dimensional layers through the crystal, and guanidinium cations. In Gu3Sb2Br9 the structural phase transformation of the first-order type is detected at 435/450 K (on cooling/heating) by the DSC and dilatometric techniques. The dielectric relaxation process in the frequency range between 75 kHz and 5 MHz over the low temperature phase indicates reorientations of weakly distorted guanidinium cations. The proton 1H NMR second-…