Three ion-pair complexes, [RbzPy](+)[Ni(mnt)(2)](-) (mnt(2-) = maleonitriledithiolate; [RbzPy](+) = 4-R-benzylpyridinium; R = Br (1), Cl (2), and NO2 (3)), with unusual magnetic properties have been synthesized and characterized. The crystal structures of 1 and 2 have been solved. The two complexes belong to the P2(1)/c space group with Z = 4 and C20H11BrN5NiS4, a = 12.0744(17) Angstrom, b = 26.369(4) Angstrom, c = 7.440(3) Angstrom, and beta = 102.63(3)degrees for 1 and C20H11ClN5NiS4, a = 12.105(2) Angstrom, b = 26.218(4) Angstrom, c = 7.374(2) Angstrom, and beta = 102.55(2)degrees for 2, respectively. The [Ni(mnt)(2)](-) anions in 1-3 form uniformly spaced one-dimensional (1-D) magnetic chains of s = 1/2 at room temperature. The temperature dependences of the susceptibility for 1-3 show that they undergo phase transitions. All three complexes are paramagnetic in their high-temperature (abbreviation HT) phase and diamagnetic in the low-temperature (abbreviation LT) phase because of strong dimerization along the stacking direction. The results of thermal analysis (DSC) further confirm that the phase transition for 1 and 2 is first-order but maybe second-order for 3. The phenomena observed in this study are similar to those of the 1-D radical systems.