Three copper (I) complexes with tetrakis(methylthio)tetrathiafulvalene (TMT-TTF), [(Cu-2(mu-X)(2)(mu-TMT-TTF)](infinity) (X = Cl, 1; X = Br, 2; and X = I, 3) were synthesized and their molecular structures and packing were determined by using single crystal X-ray diffraction methods. 1 is 2D sheet composed of TMT-TTF molecules arranged between new zigzag frames of CuCl and 3D structure is formed through S ... S contacts of 3.53 and 3.63 Angstrom between the 2D sheets. 2 has a 2D structure in which TMT-TTF molecules are connected between novel helical frames of CuBr and the S ... S contacts of 3.68 Angstrom exist between the neighboring molecules. The methyl thioether groups of TMT-TTF in 3 are coordinated to the coppers of rhomboid Cu2I2 to give linear chains. The black I-2-doped compounds 1-3 show a new broad band at ca 880 nm indicative of the oxidation of TMT-TTF molecules and gave electric conductivities of 10(-3.6), 10(-2.1), and 10(-1.7) S cm(-1), respectively. Crystal data : 1, monoclinic P2(1)/n, a = 6.657(8) Angstrom, b = 6.23(1) Angstrom, c = 24.067(8) Angstrom, beta = 91.77(7)degrees, V = 998(2) Angstrom(3), Z = 4, 1913 reflections, R = 0.028; 2, monoclinic C2/c; a = 15.443(3) Angstrom, b = 4.906(4) Angstrom, c = 26.686(1) Angstrom, beta = 96.36(1)degrees, V = 2009(2) Angstrom(3), Z = 8, 1304 reflections, R = 0.037; 3, monoclinic C2/m, a = 7.921(3) Angstrom, b = 13.266(6) Angstrom, c = 10.498(6) Angstrom, beta = 107.79(4)degrees, V = 1052(2) Angstrom(3), Z = 8, 1072 reflections, R = 0.027.