A copper(I) complex with 4,5-ethylenedithio-1,3-dithiole-2-thione (C 5 H 4 S 5 ), [Cu 4 I 4 (C 5 H 4 S 5 ) 4 ] ∞ , was synthesized and the molecular structure and packing were characterized crystallographically. The metal center is a stepped Cu 4 I 4 core coordinated by two ligands C 5 H 4 S 5 in different ways. One is bidentate coordinated through the thiocarbonyl group and the thioether group and the other is monodentate coordinated only through thiocarbonyl group. The Cu 4 I 4 clusters are bridged by bidentate C 5 H 4 S 5 molecules to form one-dimensional polymeric chains along the c-axis, and these chains form a three-dimensional network linked by interchain S S contacts. The shortest S S contact distance is 3.257(2) 9. A crystal of the complex is triclinic with space group P1, a = 11.350(5) 9, b = 11.854(3) 9 , c = 9.275(5) 9, α = 97.32(4)°, β = 112.35(4)°, γ = 67.67(2)°, V = 1067.0(9) 9 3 , Z = 2, R = 0.034, R w = 0.051.