Molecular spin ladders constructed from [Ni(dmit) ₂] ^- building blocks: Synthesis, structure and physical properties

A new ion-pair complex [1-(4-bromobenzyl)-3-methylpyridinium][Ni(dmit) ₂] (1), in which dmit = 4,5-dimercapto-1,3-dithiole-2-thione, has been synthesized and structurally characterized. The anions of [Ni(dmit) ₂] ^- stack into dimers, which further construct into a two-leg ladder through lateral S•••S interactions. The weak H-bonding interactions of C-H•••S and van de Waals interactions between anion and cations were observed. The magnetic susceptibilities measured from 2-300 K indicate an AFM exchange interaction domination and an AFM ordering below ~8 K. The best fit to magnetic susceptibility above 40 K, using a dimer model with s = 1/2, gives rise to Δ/k _B = 29.8 K, z- = -0.72 K, C = 3.40 × 10 ^-3 emu K mol ^-1 and χ ₀ = -5.8 × 10 ^-6 emu mol ^-1 with a fixed g = 2.0. Cyclovoltammetry revealed two quasi-reversible one-electron steps, which are attributed to Ni(IV/III) and Ni(III/II) redox couples.