The synthesis and characterization of a new member of the β-K2SO4 family, (Me2Et2N)2CuBr4, are reported. DSC studies indicate the presence of a phase transition at Tc=29°C with ΔS/R=13.7J/mol. The room temperature structure is monoclinic, space group, P1121/n with a=9.657(4)Å, b=15.954(6)Å, c=13.950(6)Å, γ=92.94(2)° and V=2146.3(15)Å3, with Z=4. Structural analysis gave R=0.060 and ωR=0.084 for 2098 reflections with |F|≥3σ(F). The high temperature phase is orthorhombic, space group Pmcn, with a=9.628(2), b=16.713(3), c=13.787(3)Å and V=2218.5(9)Å3 with Z=4. The structural analysis gave R=0.206 and ωR=0.227 with substantial disorder present. The room temperature structure corresponds to a B3g distortion of the parent psuedo-hexagonal Pmcn structure. The strains associated with the phase transition are particularly large. The primary structural features associated with the phase transition include rotation and disorder of the cations, displacements of the Cu and N atoms off of the mirror planar of the Pmcn phase, and rotation of the CuBr42− anions.The temperature dependencies of the lattice constants have been determined in the range 20–40°C and are indicative second order phase transition, with the phase transition occurring at Tc=33(1)°C. Both the a and c lattice constants shrink between room temperature and Tc, with c decreasing by about 1.5%. A net increase is observed in the volume by about 2%. The shrinkage in a and c is consistent with the observed reorientation of the cation described above. Considerable broadening of the diffraction peaks was observed in the temperature regime from 28–33°C, which indicates the transition is probably not a simple second order transition.