Crystal Structure and Magnetic Susceptibility Study of Pyrrolidinium Trichlorocuprate(II)

The title compound, (C4NH10)CuCl3, is shown to exist in two phases, the previously reported α phase and a new β phase. DSC studies indicate that the β phase transforms to the α phase at 93 °C. The β phase is stable at the room temperature, with the α phase metastable with respect to the β phase at room temperature. Crystals of the β phase are monoclinic, C2/c, with a = 17.327(3) A, b = 8.360(2) A, c = 12.005(2) A, and β = 100.92 (3)° with Z = 8 for ρ = 1.883 g/cm3. The structure contains chains of bibridged Cu2Cl62- dimers running parallel to the c direction. This is in contrast to the previously reported α form, which contains uniform chains of face-shared octahedra. The chains in the α phase lie parallel to the unique (monoclinic) axis. Thus, no crystallographic relationships exist between the two compounds and the phase transition must be first order in nature. A unique feature of the phase transition is a decrease in volume as the crystal is heated through the transition. This is a result of the forma...