Crystal structures, magnetic and dielectric features of two new isostructural one-dimensional platinum-bis-dithiolene molecular solids

Two new one-dimensional (1-D) molecular solids, [CH₂ = CH-BzPy][Pt(mnt)₂] (1) and [CH₂ = CH-BzPy-d₅][Pt(mnt)₂] (2) where CH₂ = CH-BzPy-d₅⁺ = 1-N-(4-vinylbenzyl) pyridinium-d₅ and mnt^2- = maleonitriledithiolate, were synthesized and characterized. A structural phase transition undergoes with T_C ≈ 335 K in the crystals of 1 and 2, which were confirmed by variable-temperature magnetic susceptibility and DSC measurements. Crystals of 1 and 2 are isostructural in both high- and low-temperature phases. Besides the strong similarity in crystal structures, they show quite analogous magnetic and dielectric features. Above T_C, the magnetic behavior is failed to follow the S = Heisenberg linear chain model; below T_C, a spin gap is opened for 1 and 2. The thermally-assisted dielectric relaxation occurs above ca. 280 K for 1 and 2, and this relaxation process is related to the dipole motion of the disordered CH₂CH groups in the cation under an ac electrical field.