Novel organic–inorganic hybrid ferroelectric: bis(imidazolium) pentachloroantimonate( iii ), (C 3 N 2 H 5 ) 2 SbCl 5

Electric permittivity, reaching ca. 4800 units at Tc, of the first haloantimonate(III) ferroelectric with R2MX5 composition characterized by unprecedented SbCl5 chains of cis-connected octahedra results from the mixed ‘order–disorder’ and ‘displacive’ mechanism of the phase transition.