Symmetry-breaking phase transitions, dielectric and magnetic properties of pyrrolidinium-tetrahalidocobaltates

We report the physicochemical characteristics of novel Co-based pyrrolidinium analogs: (C4H10N)(2)CoCl4 (PCC) and (C4H10N)(2)CoBr4 (PCB). Both compounds consist of a zero-dimensional (0D) anionic network and disordered pyrrolidinium cations. The structural origin of the anomalies observed in the electrical measurements has been confirmed by DSC thermograms and X-ray analysis. The crystals under investigations undergo a complex sequence of phase transitions: PCC at 347/353 K (phase I <-> phase II) and 202/257 K (II <-> III) and PCB at 380/381 K (I <-> II) and 256/302 K (II <-> III). The molecular motions of cations in both compounds were analysed based on proton magnetic resonance (H-1 NMR and M-2) measurements, while their magnetic properties were investigated in DC and AC modes. The DC data show magnetic anisotropy, which was confirmed by high-field HF EPR measurements. The AC susceptibility data of PCC reveal slow magnetic relaxation at the applied DC field with two relaxation channels. Given the above this organic-inorganic hybrid can be considered as a rare example of multifunctional materials which exhibit dielectric and magnetic activity.