CRYSTAL-STRUCTURE AND MAGNETIC-SUSCEPTIBILITY STUDY OF PYRROLIDINIUM TRICHLOROCUPRATE(II)

The title compound, (C4NH10)CuCl3, is shown to exist in two phases, th e previously reported alpha phase and a new beta phase. DSC studies in dicate that the beta phase transforms to the a phase at 93 degrees C. The beta phase is stable at the room temperature, with the a phase met astable with respect to the beta phase at room temperature. Crystals o f the beta phase are monoclinic, C2/c, with a 17.327(3) Angstrom, b = 8.360(2) Angstrom, c = 12.005(2) Angstrom, and beta 100.92 (3)degrees with Z = 8 for p = 1.883 g/cm(3). The structure contains chains of bib ridged Cu2Cl62- dimers running parallel to the c direction. This is in contrast to the previously reported a form, which contains uniform ch ains of face-shared octahedra. The chains in the alpha phase lie paral lel to the unique (monoclinic) axis. Thus, no crystallographic relatio nships exist between the two compounds and the phase transition must b e first order in nature. A unique feature of the phase transition is a decrease in volume as the crystal is heated through the transition. T his is a result of the formation of the more compact chains of face-sh ared octahedra in the high-temperature phase, Magnetic susceptibility studies of the beta phase are indicative of competing ferromagnetic an d antiferromagnetic coupling, with the onset of long-range order at 7. 5 K. The data are interpreted in terms of a ladder chain consisting of ferromagnetic dimers coupled into antiferromagnetic chains through sh ort Cl-... Cl contacts.