To obtain novel single-component molecular metals, we attempted to synthesize several cobalt complexes coordinated by TTF (tetrathiafulvalene)-type dithiolate ligands. We succeeded in the syntheses and structure determinations of ((Bu4N)-Bu-n)(2)[Co(chdt)(2)](2) (1), ((Bu4N)-Bu-n)(2) Co(dmdt)(2)](2) (2), (Co(dmdt)212 (3), and [Co(dt)(2)](2) (4) (chdt = cyclohexeno-TTF-dithiolate, dmdt = dimethyl-TTF-dithiolate, and dt = TTF-dithiolate). Structure analyses of complexes 1-4 revealed that two monomeric [Co < ligand >(2)](-) or [Co(ligand)(2)](0) units are connected by two Co-S bonds resulting in dimeric [Co < ligand >(2)](2)(2-) or [Co < ligand >(2)](2) molecules. Complex 1 has a cation-anion-intermingled structure and exhibited Curie-Weiss magnetic behavior with a large Curie constant (C = 2.02 K-center dot mu center dot mol(-1)) and weak antiferromagnetic interactions (theta = -8.3 K). Complex 2 also has a cation-anion-intermingled structure. However, the dimeric molecules are completely isolated by cations. Complexes 3 and 4 are single-component molecular crystals. The molecules of complex 3 form two-dimensional molecular stacking layers and exhibit a room-temperature conductivity of sigma(rt) = 1.2 x 10(-2) S center dot cm(-1) and an activation energy of E-a = 85 meV. The magnetic behavior is almost consistent with Curie-Weiss law, where the Curie constant and Weiss temperature are 8.7 x 10(-2) K center dot emu center dot mol(-1) and -0.85 K, respectively. Complex 4 has a rare chair form of the dimeric structure. The electrical conductivity was fairly large (sigma(rt) = 19 S center dot cm(-1)), and its temperature dependence was very small ((sigma K-0.55/sigma(rt) = ca. 1:10), although the measurements were performed on the compressed pellet sample. Complex 4 showed an almost constant paramagnetic susceptibility (chi(300) (K) = 3.5 x 10(-4) emu center dot mol(-1)) from 300 to 50 K. The band structure calculation of complex 4 suggested the metallic nature of the system. Complex 4 is a novel single-component molecular conductor with a dimeric molecular structure and essentially metallic properties down to very low temperatures.