Effect of counter cationic geometry on stacking structures and magnetic properties of [Ni(mnt)₂]^- complexes

The crystal structures and magnetic properties of two new ion-pair complexes, [N-NH₂Py][Ni(mnt)₂] (1) and [N-NH₂Ql][Ni(mnt)₂] (2) (N-NH₂Py⁺ = 1-aminopyridinium, N-NH₂Ql⁺ = 1-aminoquinolinium; mnt^2- = maleonitriledithiolate) have been investigated. The differences of the molecular topology and size of the counter cation result in distinct anionic and cationic stacking patterns in the crystals, namely, in the crystal of 1 the anions (A) and cations (C) alternate to stack into a mixed column in the fashion of ...AACCAACC..., and the neighboring columns are connected together via intermolecular H-bonding interactions as well as van der Waals forces; while, in the crystal of 2, the anions and cations alternate to form a mixed columnar stack in the manner of ...ACAC..., and the adjacent columns are held together via weak van der Waals forces. Investigations of variable-temperature magnetic susceptibility indicated that 1 is a spin gap system but its magnetic behavior does not follow the Bleaney-Bowers spin dimer model; 2 shows a magnetic feature of linear decrease of χ_mT value upon cooling, and this kind of magnetic behavior is probably related to the presence of temperature independent paramagnetism.