Meso- and (1S, 2S)-diphenyl-1,2-ethanediammonium (DPEDA(2+)) complexed with [8]crown-6 were introduced into [Ni(dmit)2]-based magnetic salts as countercations. The configurational difference of DPEDA(2+) modulated the crystal structure and magnetic behavior of the salts. A two-dimensional (2D) Heisenberg antiferromagnetic square lattice was observed in (meso-diphenyl-1,2-ethane diammonium(2+)) ([18]crown-6)2[Ni(dmit)2](-)(2), which was the first example of a 2D magnetic lattice in [Ni(dmit)2](-) salts.