N,N-Diethylethylendiammonium pentachloroantimoniate(III)–N,N-diethylethylendiammonium dichloride (DEDA), chemical formula [(C 2 H 5 ) 2 NH(CH 2 ) 2 NH 3 ][SbCl 5 ][(C 2 H 5 ) 2 NH(CH 2 ) 2 NH 3 ]Cl 2 , has been synthesized and characterized by the X-ray diffraction method at 293K. It crystallizes in the orthorhombic space group Pnam with the following unit-cell dimensions: a=9.9700(0), b=10.8400(1), c=23.6360(6)Å and Z=4. The crystal structure consists of two N,N-diethylethylendiammonium cations, [SbCl 5 ] 2− anions and two isolated chloride ions. The anions, in which distorted [SbCl 5 ] 2− square pyramids share a common Cl − ion, are held together in infinite chains parallel to the a axis. These chains are themselves interconnected by N–H⋯Cl hydrogen bridge bonds. The dynamics of the proton and the molecular motion revealed dynamical phase transitions in the vicinity of 208 and 255K.