Synthesis, crystal structure and high temperature phase transition in the new organic–inorganic hybrid [N(C4H9)4]3Zn2Cl7H2O crystals
Résumé
The present paper accounts for the synthesis, crystal structure, differential scanning calorimetry and vibrational spectroscopy of a new compound tri-tetrabutylammonium heptachloro–dizincate (I) grown at room temperature by slow evaporation of aqueous solution. From X-ray diffraction data collected at room temperature, it is concluded that it crystallizes in the monoclinic system (P21/n space group) containing ZnCl42− and ZnCl3H2O1− tetrahedra. The atomic arrangement can be described by an alternation of organic and organic–inorganic layers stacked along the c direction. Differential scanning calorimetry (DSC) in the range 250–450 K disclosed a reversible structural phase transition of order–disorder type at 358 K, prior to the melting at 395 K. The temperature dependence of the Raman spectra of [N(C4H9)4]3Zn2Cl7H2O single crystals was studied in the spectral range 100–3500 cm−1 and for temperatures between 300 and 386 K. The most important changes are observed for the line at 261 cm−1 issued from ν1(ZnCl4). The analysis of the wavenumber, intensity and the line width based on an order–disorder model allowed to obtain information relative to the activation energy and the correlation length. The decrease of the activation energy with increasing temperature has been interpreted in term of a change in the re-orientation motion of the anionic parts.
The assumption of cluster fluctuations also allowed the critical exponents to be obtained for the transition δ = 0.011 and the correlation length ξ0 = 598 Å.