Four ion-pair complexes of [Ni(dmit)(2)](-) with [NO(2)bzql](+) have been obtained, which belong to two kinds of polymorph forms, [NO(2)bzql][Ni(dmit)(2)] (1 alpha and 1 beta) and [NO(2)bzql][Ni(dmit)(2)]center dot CH3COCH3 (2 alpha and 2 beta) (where dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate and [NO(2)bzql](+) = 1-(4-nitrobenzyl)quinolinium). Though 1 alpha, 2 alpha, and 2 beta all show anionic dimerization structures at room temperature, they have different anionic and cationic arrangement fashions, which give rise to different magnetic behaviors for these polymorphs or pseudo-polymorphs. Compounds 1 alpha, 1 beta, and 2 alpha exhibit magnetic bistabilities. In particular, 1 alpha has a hysteretic loop at similar to 55 K, while 2 beta does not display a spin transition in the 2-300 K range. On the basis of the crystal structure data of 2 alpha in high-and low-temperature phases, the magnetic coupling feature within the [Ni(dmit)(2)](-) spin dimer was explored with the broken-symmetry approach at the UBPW91/LANL2DZ level; combined with the experimental data and theoretical analyses, the relationship between the magnetic coupling nature and the stacking pattern of [Ni(dmit)(2)](-) anions as well as the origin of the phase interconversion are discussed.