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RESEARCH PRODUCT

Structure, phase transitions and molecular dynamics in ferroelastic crystal pyrrolidinium hexachloroantimonate(V), [C4H8NH2][SbCl6]

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Abstract The crystal structure of the pyrrolidinium hexachloroantimonate(V), [C4H8NH2][SbCl6], abbreviated PCA, has been determined by means of X-ray diffraction at 300 and 340 K. The space groups are monoclinic P 2 1 / n (phase III) and orthorhombic Pmnb (phase II), respectively. The crystal undergoes two structural phase transitions: first-order type at 356/329 K (heating/cooling) from phase (I) to (II) and second-order type at 323 K from phase (II) to (III). Dielectric studies suggest the plastic crystals behaviour above 356 K (phase I). Proton spin-lattice relaxation time ( T 1 ) and second moment ( M 2 ) of polycrystalline [C4H8NH2][SbCl6] have been determined at 77–370 K, at 90 and 25 MHz. Temperature dependence of the M 2 indicates that the continuous increase in the freedom of rotational motion of the pyrrolidinium cations takes place over the phase (III). The ferroelastic domain structure of [C4H8NH2][SbCl6] is observed over the phase (III). Mechanisms of phase transitions in PCA are discussed.