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

Abstract

We report the physicochemical characteristics of novel Co-based pyrrolidinium analogs: (C₄H₁₀N)₂CoCl₄ (PCC) and (C₄H₁₀N)₂CoBr₄ (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 (¹H NMR and M₂) 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.