The mono- and binuclear aryldiazene complexes [Re(C6H5N=NH)(Co)(5-n)P-n]BY4 (1-5) and [{Re(CO)(5-n)P-n}(2)(mu-HN=NAr-ArN=NH)](BY4)(2) (6-12) [P = P(OEt)(3), PPh(OEt)(2), PPh2OEt; n = 1-4; Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-(2-CH3)C6H3-C6H3(2-CH3), 4,4'-C6H4-CH2-C6H4; Y = F, Ph) were prepared by reacting the hydride species ReH(CO)(5-n)P-n with the appropriate mono- and bis(aryldiazonium) cations. These compounds, as well as other prepared compounds, were characterized spectroscopically (IR; H-1, P-31, C-13, and N-15 NMR data), and 1a was also characterized by an X-ray crystal structure determination. [Re(C6H5N=NH)(CO){P(OEt)(3)}(4)]BPh4 (1a) crystallizes in space group P (1) over bar with a = 15.380(5) Angstrom, b = 13.037(5) Angstrom, c = 16.649(5) Angstrom, alpha = 90.33(5)degrees, beta = 91.2(1)degrees, gamma = 89.71(9)degrees, and Z = 2. The "diazene-diazonium" complexes [M(CO)(3)P-2(HN=NAr-ArN=N)](BF4)(2) (13-15, 17) [M = Re, Mn; P = PPh2OEt, PPh2OMe, PPh3; Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-C6H4-CH2-C6H4] and [Re(CO)(4)(PPh2OEt)(4,4'-HN=NC6H4-C6H4N=N](BF4)(2) (16b) were synthesized by allowing the hydrides MH(CO)(3)P-2 or ReH(CO)(4)P to react with equimolar amounts of bis(aryldiazonium) cations under appropriate conditions. Reactions of diazene-diazonium complexes 13-17 with the metal hydrides M2H(2)P(4)' and M2'H(CO)(5-n)P-n("), afforded the heterobinuclear bis(aryldiazene) derivatives [M1(CO)(3)P-2(mu-HN=NAr-ArN=NH)M2HP(4)'](BPh4)(2) (ReFe, ReRu, ReOs, MnRu, MnOs) and [M1(C0)(3)P-2(mu-HN=NAr-ArN=NH)M2'-(CO)(5-n)P-n(")](BPh4)(2) (ReMn, MnRe) [M1 = Re, Mn; M2 = Fe, Ru, Os; M2' = Mn, Re; P = PPh2OEt, PPh2OMe; P', P " = P(OEt)(3), PPh(OEt)(2); Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-C6H4-CH2-C6H4; n = 1, 2],The heterotrinuclear complexes [ReCCO)(3)(PPh2OEt)(2)(mu-4,4'-HN=NC6H4-C6H4N=NH)M{P(OEt)(3)}(4)(mu-4,4'-HN=NC6H4-C6H4N=NH)Mn(CO)(3)(PPh2OEt)(2)](BPh4)(4) (M = Ru, Os) (ReRuMn, ReOsMn) were obtained by reacting the heterobinuclear complexes ReRu and ReOs with the appropriate diazene-diazonium cations. The heterobinuclear complex with a bis(aryldiazenido) bridging ligand [Mn(CO)(2)(PPh2OEt)(2)(mu-4,4'-N2C6H4-C6H4N2)Fe{P(OEt)(3)}(4)]BPh4 (MnFe) was prepared by deprotonating the bis(aryldiazene) compound [Mn(CO)(3)(PPh2OEt)(2)(mu-4,4'-HN=NC6H4-C6H4N=NH)Fe(4-CH3C6H4CN){P(OEt)(3)}(4)](BPh4)(3). Finally, the binuclear compound [Re(CO)(3)(PPh2OEt)(2)(mu-4,4'-HN=NC6H4-C6H4N2)Fe(CO)(2){P(OPh)(3)}(2)](BPh4)(2) (ReFe) containing a diazene-diazenido bridging ligand was prepared by reacting [Re(CO)(3)(PPh2OEt)(2)(4,4'-HN=NC6H4-C6H4N=N](+) with the FeH2(CO)(2){P(OPh)(3)}(2) hydride derivative. The electrochemical reduction of mono- and binuclear aryldiazene complexes of both rhenium (1-12) and the manganese, as well as heterobinuclear ReRu and MnRu complexes, was studied by means of cyclic voltammetry and digital simulation techniques. The electrochemical oxidation of the mono- and binuclear aryldiazenido compounds Mn(C6H5N2)(CO)(2)P-2 and {Mn(CO)(2)P-2}(2)(mu-4,4'-N2C6H4-C6H4N2) (P = PPh2OEt) was also examined. Electrochemical data show that, for binuclear compounds, the diazene bridging unit allows delocalization of electrons between the two different redox centers of the same molecule, whereas the two metal centers behave independently in the presence of the diazenido bridging unit.