Isostructural phase transition and dielectric reversibility in a cobalt thiocyanate complex incorporating an organic-inorganic hybrid compound: (C5H7N2)2[Co(NCS)]4

Abstract

In this study, a novel inorganic-organic hybrid crystalline material (C5H7N2)2[Co(NCS)4] (compound 1) was obtained by adopting the natural evaporation method using cobalt(II) chloride hexahydrate, ammonium thiocyanate, and 4-aminopyridine as raw materials. The structure and properties of the compounds were characterized by variable-temperature infrared spectroscopy, single-crystal X-ray diffraction (XRD), thermogravimetric analysis (TGA), powder XRD, differential scanning calorimetry (DSC), and dielectric tests. The results revealed P21/c as the space group of compound 1, wherein one-dimensional chains and a two-dimensional mesh structure were formed via combined hydrogen bonding and π···π interactions between the cobalt thiocyanate complex and the protonated 4-aminopyridine, exhibiting noticeable telescopic motions with changes in temperature. The DSC results showed that the compound generated a reversible phase-transition thermal energy peak near 240 K, with the reversible dielectric cycling changes being consistent with the thermal energy changes. This finding highlighted the isostructural phase transition and dielectric reversibility attributes of the herein synthesized compounds, accentuating their multifunctionality and excellent electrochemical properties.