Structure and properties of [(CH3)4P]3[Sb2Cl9] and [(CH3)4P]3[Bi2Cl9

Abstract

Two new phosphonium chloroantimonate(III) and chlorobismuthate(III) crystals([(CH3)4P]3[Sb2Cl9] (PCA)and [(CH3)4P]3[Bi2Cl9] (PCB)) have been synthesized and their structure determined by means ofsingle-crystal x-ray diffraction. The structure of the title compounds contains discrete[M2Cl9]3− anions in generalpositions and disordered [(CH3)4P]+ cations. The two compounds are isomorphous in the roomtemperature phase and crystallize in the polar trigonal space group,P31c. The phase situation in PCA and PCB is established on the basis of differential scanningcalorimetry and dilatometric studies. Two phase transitions are found: at 534/534 K() and at 135/138 K () for PCA and at 550/550 K () and at 151/155 K () for PCB (on cooling/heating). The values of the transition entropies(ΔStr) obtained suggest that the transitions are of the order–disorder type. The dielectric dispersion measurements haverevealed a relaxation process in the PCB crystal. The pyroelectric measurements of bothcompounds have confirmed the polar nature of the low temperature phase (III). The ferroic(ferroelastic) properties were found over phase III for both crystals.