A metal-dimer assembled system, M-2(dtp)(4) (M = Ni, Pd; dtp = dithiopropionate, C2H5CS2-), was synthesized and analyzed by the X-ray single-crystal diffraction method, UV-vis-near-IR spectra of solutions, solid-state diffuse reflectance spectroscopies, and electrical conductivity measurements. The structures exhibit one-dimensional metal-dimer chains of M-2(dtP)(4) with moderate interdimer contact. These complexes are semiconducting or insulating, which is consistent with the fully filled d(Z2) band of M-II(d(8)). Interdimer metal-metal distances were 3.644(2) angstrom in Ni-2(dtp)(4) and 3.428(2) angstrom in Pd-2(dtp)(4), each of which is marginally longer than twice the van der Waals radius of the metal. Interdimer charge-transfer transitions were nevertheless observed in diffuse reflectance spectra. The origin of this transition is considered to be due to an overlap of two adjacent d(a*) orbitals, which spread out more than the d(Z2) orbital because of the antibonding d(sigma*) character of the M(d(Z2))-M(d(Z2)). The Ni-2(dtp)(4) exhibited an interdimer charge-transfer band at a relatively low energy region, which is derived from the Coulomb repulsion of the 3d(sigma*). orbital of Ni.