Synthesis, crystal structure, thermal and dielectric properties of bis(2,4-diammonium toluene) decachlorodibismuthate(III) tetrahydrate [C7H12N2]2Bi2Cl10·4H2O

The compound [C7H12N2]2Bi2Cl10·4H2O crystallizes in the monoclinic system with the P21/c space group. The crystal structure can be described as a stack of organic–inorganic layers along the [0 1 0] direction. The organic part consists of one organic cation type which orients its two amine groups to the neighboring anions. The inorganic entity is made up of [Bi2Cl10]4− dimers composed of two equivalent irregular octahedrons sharing one edge. The water molecules are sandwiched between the [Bi2Cl10]4− anion and its neighboring [C7H12N2]2+ cations. The crystal packing is governed by N–H⋯Cl, N–H⋯OW and OW–H⋯Cl hydrogen bonds, forming a three dimensional network. The 13C CP-MAS-NMR spectrum shows seven isotropic resonances, confirming the existence of seven non-equivalent carbon atoms. This is in good agreement with the crystal structure study. Raman and infrared spectra at room temperature were recorded in the 7–350 and 400–4000 cm−1 frequency regions, respectively. This study confirms the presence of the organic cation [C7H12N2]2+ and the bi-octahedron [Bi2Cl10]4−. Differential scanning calorimetry (DSC) has revealed a structural phase transition of the order–disorder type around 312 K. The evolution of the dielectric constant as a function of temperature and frequency of this compound has been investigated in order to discuss the mechanism of the phase transition.

The structure of [C7H12N2]2Bi2Cl10·4H2O is built from dimeric [Bi2Cl10]4− entities with the geometry of two octahedrons sharing one edge, in the presence of diprotonated 2,4-diammonium toluene cations and water molecules. The 13C CP-MAS-NMR spectrum confirms seven different isotropic peaks corresponding to the carbon atoms of one organic cation in the structure. The dielectric constant has been studied in order to discuss the mechanism of the phase transition in this compound.Figure optionsDownload as PowerPoint slide