The simultaneous desulfurization of 2-mercapto-5-methyl-1,3,4-thiadiazole with CuCl2·2H2O via mutual diffusion in solvents results in the isolation of air-stable dark-green crystals of [Cu(H4C3N2S)Cl2]n (∼65% yield). The structure is characterized by a unique one-dimensional copper chain bridged by diazine N-N single bonds rather than halogens, in sharp contrast with the halide bridging mode in conventional copper halide coordination polymers. Each Cu(II) ion shows a square planar coordination geometry featuring a strong Jahn-Teller distortion, as also supported by EPR data. The phase follows a Curie-Weiss paramagnetic behavior over 6-300 K. However, the intrachain antiferromagnetic interaction is evident (-2J = 21.1 cm-1). Such magnetic coupling is related to the interplay between the Cu(II)-dx2-y2 and diazine N-N p-orbitals.