Three new compounds were obtained by slow diffusion of [Ni(dmit)(2)](-) (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato) into 4-(dimethylamino)-1-methylpyridinium [C-1](+), 4-[2-(4-(dimethylamino)phenyl)ethenyl]-1-methylpyridinium [C2](+), and 4-[4-(4-(dimethylamino)phenyl)-1,3-butadienyl]-1-methylpyridinium [C-3](+). [C-1](+)[Ni(dmit)(2)](-) exhibits two crystallographic phases (1, 2) as does [C-2](+)[Ni(dmit)(2)](-) (3, 4). The structures have been determined : 1, monoclinic, P2(1)/c, a = 17.450(2) Angstrom, b = 10.646(1) Angstrom, c = 23.891(2) Angstrom, beta = 97.42(1)degrees, Z = 4; 2, triclinic P (1) over bar, 9.776(1) Angstrom, b = 15.195(2) Angstrom, c = 16.999(2) Angstrom, alpha = 114.14(1)degrees, beta = 101.84(1)degrees, gamma = 93.40(1)degrees, Z = 2; 3, monoclinic, P2(1)/c, a = 9.813(1) Angstrom, b = 11.589(1) Angstrom, c = 24.345(3) Angstrom, beta = 93.12(1)degrees, Z=4; 2, triclinic, P (1) over bar, a = 13.432(2) Angstrom, b = 16.101(2) Angstrom, c = 6.553(1) Angstrom, alpha = 99.69(1)degrees, beta = 94.34(1)degrees, gamma = 102.88(2)degrees, Z = 2; [C-1](+)[Ni(dmit)(2)](-) (1) exhibits a conductivity of 1.3 x 10(-2) S cm(-1). Due to centrosymmetry, none of the materials exhibits second-order nonlinear optical properties, but the structure of 1 demonstrates that layers of highly polarizable cations can be stabilized in a noncentrosymmetric environment between two-dimensional networks of [Ni(dmit)(2)](-) species.