Observation of an unusual hysteretic magnetic transition in a heteroleptic nickel-bis-1,2-dithiolene compound

A heteroleptic nickel-bis-1,2-dithiolene ion-pair complex, [BzQl][Ni(dmit)(mnt)] (where BzQl⁺ = 1-(benzyl)quinolinium; dmit ^2- = 2-thioxo-1,3-dithiole-4,5-dithiolate, mnt^2- = maleonitriledithiolate), was synthesized and characterized structurally, which exhibited novel magnetic bistability. The compound crystallized in triclinic system with space group P-1. The anions and cations form alternating layered alignments, and the anionic layer is built by the irregularly heteroleptic [Ni(dmit)(mnt)]^- chains, where the neighboring anions are connected via lateral-to-lateral S...S contacts of dmit^2- ligands. The temperature dependences of magnetic susceptibility follow the S = 1/2 Heisenberg alternating linear-chain model in high-temperature phase and Curie-Weiss law in low-temperature phase.