The structure of [C2H5NH(CH3)(2)(+)](3)[BiCl6-] (abbreviated as DCB) was determined by a single-crystal X-ray diffraction at 115K. The compound adopts tetragonal symmetry with the space group I4(1)/acd; a = 23.35 angstrom, c = 17.60 angstrom, V = 9598 angstrom(3) and Z = 16. The crystal structure of DCB is built up of isolated [BiCl6](3-) units and N,N-dimethylethylammonium counterions that are accommodated in the large voids. At ambient temperature two-thirds of the counterions appear to be dynamically disordered. Dynamics of this type of cations contributes to the enhanced dielectric permittivity of DCB. A low frequency dielectric relaxation process that takes place between 200 and 300 K is characterized by an exceptionally large dielectric increment, Delta epsilon > 100, which is unprecedented in nonferroelectric materials. The molecular motions of the N,N-dimethylethylammonium cations were studied by means of H-1 NMR spin-lattice relaxation time measurements. (C) 2012 Elsevier Ltd. All rights reserved.