Unprecedented solid-state chemical reaction—from (C3N2H5)3SbBr6·H2O to (C3N2H5)5Sb2Br11. From centrosymmetric to non-centrosymmetric crystal structure
Abstract
Tris(imidazolium) hexabromoantimonate(III) hydrate, (C3N2H5)3SbBr6·H2O, (abbreviated as TIBA) has been synthesized and characterized by X-ray (at 295, 225, 160, and 110 K), differential scanning calorimetry, dilatometry, and dielectric spectroscopy. At room temperature (phase I), the structure consists of discrete SbB 6- anions, disordered imidazolium cations, and water molecules forming a 3D array of hydrogen bonds. Below room temperature, TIBA was found to undergo isostructural discontinuous phase transition at 212/221 K (cooling-heating) (P21/c↔P21/c). The phase transition mechanism is characterized by two contributions: an order-disorder (cationic substructure) and a displacive (water molecules) one. At high temperatures, the TIBA crystal was found to undergo an unprecedented in situ solid-state chemical reaction: 2(C3N2H5)3SbBr6·H2O→(C3N2H5)5Sb2Br+(C3N2H5)Br+2H2O This chemical transformation leads to multiphase crystallites dominated by an amorphous phase of (C3N2H5)5Sb2Br11. The creation of ferroelectric crystallites - (C3N2H5)5Sb2Br11 - in an "annealed" sample of (C3N2H5)3SbBr6·H2O was confirmed by X-ray diffraction phase analysis, dielectric spectroscopy, and pyroelectric measurements. The dielectric response of the electric permittivity and the critical slowing down of the process observed near 140 K in the "annealed" sample of TIBA are treated as a "fingerprint" of a neat (C3N2H5)5Sb2Br11 ferroelectric.
- Publication:
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Journal of Solid State Chemistry France
- Pub Date:
- December 2010
- DOI:
- 10.1016/j.jssc.2010.10.020
- Bibcode:
- 2010JSSCh.183.3058P