The Long-Chain N-Alkylpyridinium Cation Modulate Magnetic Behaviors of Metal-bis-1,2-dithiolene Compounds

Abstract

Two metal-dithiolene compounds with a formula of [Cn-py][Ni(mnt)2] (Cn-py+ represents the 1-alkyl-pyridinium cation, n = 8 (denoted as compound 1), and 9 (denoted as compound 2); mnt2− = maleonitriledithiolate) were synthesized and characterized. The crystal structures determined for two compounds disclosed that these are isostructural with similar cell parameters and packing structures. The cation adopts a bent conformation and the direction of the hydrocarbon chain is approximately parallel to the long molecular axis of the [Ni(mnt)2]− anions, and the [Ni(mnt)2]− anions and cations of 1 and 2 form segregated irrequidistant columns stacks along the crystallographic c-axis direction. It is worth noting that there existed charge assisted C–H···N interactions between the adjacent anion and cation stacks in crystal of 1 and 2. DSC measurement of 1 and 2 exhibited two exothermic peaks in the first and second cooling process, and showed supercooling behavior and the thermal hysteresis of 18 and 50 K were observed for 1 and 2, respectively. Furthermore, 1 exhibits cold crystallization around 342 K during the second heating scan. Compound 1 shows the magnetic characteristics of a low-dimension antiferromagnetic coupling spin system in the high temperature and spin gap in the low-temperature phase, and compound 2 exhibits weak paramagnetism over the temperature range of 2–400 K. Compound 1 shows the magnetic characteristics of spin gap in the low-temperature phase and 2 exhibits weak paramagnetism over the temperature range of 2–400 K.