Crystal structure, magnetic, near-infrared absorption and electrochemical properties of two [Ni(mnt)₂]^- based compounds

Two ion-pair compounds with the formula of (BMIB)[(Ni(mnt)₂]₂ (1) and (BMIO)[(Ni(mnt)₂]₂ (2) (mnt= maleonitrile dithiolate, BMIB=1,4-bis(1-methylimidazolium)butane, BMIO=1,8-bis (1-methylimidazolium)octane) were synthesized and characterized structurally. In 1, the [Ni(mnt)₂]^- form a trimer anions and a mixed column, respectively. The packing structures of 2 are different from 1, the cations and the anions form the irregular alignments. Compound 1 and 2 show remarkable near-IR absorption behavior in the region of 861 and 857 nm respectively. The electrochemical behaviors in the solid state depend on the hydrocarbon chain length in the countercation moiety. Investigations of variable-temperature magnetic susceptibility indicated that 1 shows weak paramagnetic feature from 2 to 400K; the magnetic susceptibility data were fit to the Curie-Weiss equation. 2 is a spin gap system but its magnetic behavior does not follow the Blaney-Bowers spin dimer model. CCDC: 908109, 1; 908110, 2.