In this paper we described dimeric complexes of Cu(I) with 4,4′,5,5′-tetracyano-2,2′-biimidazole (H2Tcbiim). These compounds contain the dianion (Tcbiim2-) acting as a quadridentate bridge betwee Cu(I) ions in combinations with phosphine, phosphite, pyridine, and quinuclidine ligands. Syntheses and interconversions among these species are recorded. The structure of Cu2[P(OPh)3]2(Py)2Tcbiim Py was determined by X-ray crystallography. The composition Cu2P2O6C61N11H45 crystallizes in the P1 triclinic space group with a = 10.456(3) Å, b = 15.060(5) Å, c = 10.438(2) Å, α = 94.89(2), β = 115.93(2), γ = 72.76(2) and Z = 1 molecule per cell. A final agreement of R = 0.035, Rw = 0.042 was obtained for 2743 observed reflections. The dimeric molecule has an inversion center between the 2,2′ carbon atoms of Tcbiim2-. Each Cu atom is tetrahedrally coordinated with angles ranging from 101°-126°. As a result of steric crowding by the phenyl rings of P(OPh)3 the copper atoms are somewhat sequestered. The influence of the stric and electronic factors can be seen in the oxidation potentials obtained from cyclic voltammetry. The potentials for the successive one electron oxidation of the dimers vary greatly with the donor strength of the ligands. © 1984.