A series of mixtures of symmetric metal complexes of C 3 S 5 - and C 3 S 4 Se 2- ligands (C 3 S 5 - 1,3-dithiole-2-thione-4,5-dithiolate, DMIT; C 3 S 4 Se 2- = 1,3-dithiole-2-selone-4, 5-dithiolate, DMISE), [Bu 4 N] 2 [M(C 3 S 4.4 Se 0.6 ) 2 ] (MNi, 1 ; M = Cu, 2), [Bu 4 N] [Ni(C 3 S 4.4 Se 0.6 ) 2 ], 3, [Bu 4 N] 2 [Ni(C 3 S 4.7 Se 0.3 ) 2 ], 4, and [Bu 4 N][Ni(C 3 S 4.7 Se 0.3 ) 2 ], 5, have been prepared. Oxidation reactions of 1 with excess iodine afforded the neutral complex [Ni(C 3 S 4.4 Se 0.6 ) 2 ], 6, which exhibited electrical conductivity of 0.29 S cm -1 at 25°C for a compacted pellet. Single-crystal X-ray analysis of 1 revealed that the anion structure as a whole is planar. Both 3 and 5 form a one-dimensional arrangement through the intermolecular sulfursulfur contacts. The S and Se at the terminal positions of the ligand are disordered. A single-crystal ESR study on [BuN 4 ] 2 [Cu/Ni(C 3 S 4.4 Se 0.6 ) 2 ] demonstrated that the M-S coordination bond in the complex has a strong covalent σ-bond character.