[BDTA](2)[Cu(mnt)(2)] (BDTA = benzo-1,3,2-dithiazolyl, mnt = maleonitriledithiolate) was crystallized in the space group P1 with an inversion center on Cu giving a stacked structure with each metal complex anion sandwiched by two cations. Short intermolecular S...S contacts give rise to a one-dimensional chain lateral to the stacking axis. Variable-temperature magnetic susceptibility and EPR measurements indicate that the salt behaves as an ideal one-dimensional Heisenberg antiferromagnetic material from 2 K less than or equal to T less than or equal to 300 K, with a coupling constant of J/k(B) = 16-17 K; the very low temperature magnetic properties are in quantitative agreement with the predictions of quantum field theory. DFT calculations are consistent with the formation of a one-dimensional magnetic chain with interstack interactions mediated by the BDTA counterions.