A new Cr(III) bis-acetylide complex containing redox-active ethynyl-substituted 4-methyl-4′,5′-trans-diethyl-ethylenedithio-tetrathiafulvalene, [Cr(III)cyclam(C≡C-MeEt2EDT-TTF)2]n+ (n+) was synthesized. The crystal structures of two salts, [Ni(dmit)2] (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate) and [Ni(mnt)2]3 (mnt = maleonitriledithiolate), were determined by single-crystal X-ray diffraction. In the crystal of [Ni(dmit)2], the trans-diethyl group of + is in the axial position and prevents π-stacking of the TTF units, resulting in a negligibly weak spin–spin interaction between Cr3+ and [Ni(dmit)2]−. In contrast, in [Ni(mnt)2]3, the trans-diethyl group is in the equatorial position in [Ni(mnt)2]3 owing to the strong attractive force between the π-stacked TTF+ units and the [Ni(mnt)2]− anions. This π-stacking has a significant effect on the magnetic property of  [Ni(mnt)2]3. The π-stacked TTF+ units and [Ni(mnt)2]− anions behave approximately as a one-dimensional S = 1/2 antiferromagnetic chain connecting the spins of Cr3+ antiferromagnetically.