One-electron oxidation of tetrakis(methylthio)tetrathiafulvalene (TTC1TTF) by CuBr2 yields a black copper(I) coordination compound, [(TTC1TTF)CuBr2](2) (1), whose structure has been determined by means of X-ray crystallography. 1 has a dimer structure consisting of a Cu2Br2 rhomboid with terminal Br- and TTC1TTF+ which coordinate to Cu(I) through one of four SMe groups. TTC1TTF+ form columnar stacks with the shortest S ... S contact of 3.44 Angstrom. Since most of TTC1TTF+ cation radicals in crystal form spin-pairs, a weak ESR signal observed at g = 2.008 is attributed to TTC1TTF+ radicals remain as free from pair formation located at crystal surface. Crystal Data : triclinic (P (1) over bar), a = 10.053(1) Angstrom, b = 10.618(1) Angstrom, c = 9.722(2) Angstrom, alpha = 90.85(1)degrees, beta = 91.04(1)degrees, gamma = 110.487(9)degrees, V = 971.7(3) Angstrom(3), Z = 1, R = 0.036, R(W) = 0.036.