Phase transition in bis(ethyldimethylammonium) pentachloroantimonate(III)

The crystal structure of a new member of the alkylammonium chloroantimonate family, namely bis(ethyldimethylammonium) pentachloroantimonate(III), [C2H 2NH(CH3)(2)](2)[SbCl5], was determined at room temperature. The anionic sub lattice consists of isolated distorted square-pyramidal [SbCl5](2-) units a nd two crystallographically inequivalent disordered ethyldimethylammonium c ations connected to anions by N-H ... Cl hydrogen bonds. The disorder is re alised by the presence of two positions for all C, N and H atoms, and is ex plained as being a result of the overall reorientation of cations along the long axis of the molecule. One second-order phase transition was found at ca 160 K and results in a lowering of the symmetry from orthorhombic to mon oclinic or triclinic.