New mixed-valence Cu-I-Cu-II coordination polymers with one-dimensional, infinite-chain structures, [(Cu2CuX2)-Cu-I-X-II(Hm-dtc)(2)(CH3-CN)(2)](n) [Hm-dtc(-) = hexamethylene dithiocarbamate, X = Br- (1), I- (2)], have been prepared and structurally characterized by X-ray diffraction. These complexes consist of a mononuclear copper(II) unit Cu-II(Hm-dtc)(2) and dinuclear copper(I) units Cu-2(I)(CH3CN)(2)X-2. Magnetic studies have revealed that these complexes have a relatively strong antiferromagnetic interaction [J = -26.9 cm(-1) (1) and J = -22.2 cm(-1) (2)] between the unpaired electrons of the Cu-II ions through the dinuclear copper(I) halide unit of (Cu2X2)-X-I in the chain. The electrical properties of 1 and 2 are investigated using an impedance spectroscopy technique, and it is revealed that these complexes exhibit intriguing semiconducting properties with small activation energies [E-a = 0.562 eV (1) and E-a = 0.479 eV (2)].