Crystal structure, DSC, TGA and electrical studies of Bis (1,12-dodecamethylenediammonium hexachlorobismuthate chloride dihydrate (C12H30N2)2BiCl6.Cl·2H2O

Abstract (C12H30N2)2BiCl6.Cl·2H2O compound crystallizes at 296 K in triclinic system with P-1 space group [Z = 2; a = 10.532(3) A, b = 12.143(4) A, c = 16.295(5) A; α = 97.543(13)°, β = 101.451(14)°, δ = 97.484(13)°]. DSC analysis showed three anomalies (338 K, 347 K, and 367 K) in heating, not reproducible in cooling, which are due to dehydratation process, above which a stable anhydrous compound undergoes a second order phase transition at 483/470 K (heating/cooling). TG-DTG analyses showed that the weight loss is due to removing of crystallization water from the hydrate compound, which is confirmed by the Infrared spectra recorded at room temperature and at 408 K. The X-rays powder diffraction pattern of the dehydrated compound (408 K) is well indexed in triclinic unit cell with a non centrosymmetric space group P1 [a = 11.467(62) A, b = 16.671(14) A, c = 9.787(11) A; α = 103.822(13)°, β = 95.194(12)°, δ = 96.614(13)°]. Dielectric constant (er) evolution with temperature and frequency showed that the dehydrate compound may be a relaxor ferroelectric below the diffuse phase transition (Tm = 473 K at 1 MHz). Cole-Cole plots of impedance complex have been performed. The Vogel-Fulcher-Tammann (VFT) model is used in analysis of experimental data of temperature dependence of the relaxation time. The temperature dependence of frequency exponent n implies that the conduction mechanism may be due to the small polaron tunnelling SPT model below the phase transition temperature Tm.