Observation of magnetic behavior with two broad maxima of magnetic susceptibility in [Ni(mnt)2]− complexes

Three complexes of [Ni(mnt)2]− (mnt2− = maleonitriledithiolate) with benzylpyridinium derivatives, 1-(2′,6′-dichlorobenzyl)-4-aminopyridinium (abbr. Cl2BzNH2Py+) and 1-(2′,6′-dichlorobenzyl)quinolinium (abbr. Cl2BzQl+), have been characterized structurally and magnetically. The [Cl2BzNH2Py][Ni(mnt)2] solution in MeCN was slowly evaporated to give the crystals of 2, whilst its solution in i-PrOH/MeCN yields 2·0.5i-PrOH. The [Ni(mnt)2]− anions are arranged in the mixed stacks of anions and cations in 2, and the segregated stacks of anions and cations in 2·0.5i-PrOH and 4. Even though three complexes exhibit different stacking pattern of magnetic anions, their temperature dependences of magnetic susceptibilities in 2-300 K range show a common feature, namely, two broad maxima of magnetic susceptibility. Powder X-ray examination for three complexes excluded that the impurity causes such complicated magnetic behaviors. Combined with the single crystal structure analyses, the double broad maxima of magnetic susceptibility is probably attributed to anisotropic magnetic exchange interactions between magnetic anions.