A new chlorocuprate(II), [(C2H5)(4)N]2Cu5Cl12, was prepared by reaction of CuCl2 .2H2O and (C2H5)(4)NCl in 1,1,2-trichloroethane-ethanol followed by water-ethanol evaporation. The crystal structure, solved by single-crystal X-ray diffraction at room temperature, was found to be triclinic, space group P (1) over bar, with cell parameters a = 8.9123(9) Angstrom, b = 11.0690(8) Angstrom, c = 21.2211(9) Angstrom, alpha = 118.766(6)degrees beta = 109.041(8)degrees, gamma = 97.465(7)degrees, and Z = 1, and consists of a two-dimensional network of [(Cu5Cl(12))(2-)]infinity parallel to the a, b plane, alternating with layers of the organic cations along c. The anionic sheets are built up by aggregation of infinite zigzag chains of alternating tetranuclear and mononuclear subsequences. This structure can be related to the anhydrous CuCl2 structure by systematic removal of (Cu(2)C1(6))(2+) fragments. The magnetic susceptibility of this compound can be described by a simple model, suggested by the structural data, that considers independent contributions of linear tetramers, with antiferromagnetically coupled pairs of copper atoms (J(l)/k = -64(2) K), and almost magnetically isolated Cu(II) centers, that obey a Curie-Weiss law with a Theta = -2.7(8) K.