A series of binuclear [Ru-2(ttha)](n-) complexes, ttha(6-) = triethylenetetraminehexaacetate, have been prepared. These include [Ru-2(II)(ttha)(H2O)(2)](2-) = (II,II), [Ru-2(III)(ttha)(H2O)(2)] = (III,III), [(RuRuIII)-Ru-II(OH)(ttha)](2-) = (II,III), and [(RuORuIV)-O-III(ttha)](-) = (III,IV). The stable forms of (II,II) and (III,III) are the extended chain species having separate Ru centers in chemical binding sites virtually equivalent to the monomeric [Ru-II/III(hedta)](-/0) complexes. CO complexes of (II,II) and the open-chain isomer (II,III)(0), which exists below pH 4, readily form (nu(CO) = 1943 and 1941 cm(-1), respectively) showing the presence of labile Ru-II-OH2 sites. Above pH 5 (II,III) exists as the hydroxy-bridged Ru-II(OH-)Ru-III mixed-valence species having a band at 527 nm (epsilon/Ru = 1.47 x 10(3) M(-1) cm(-1)) which is most likely of sigma*(d(x2)-(y2), d(z2)) <-- d pi* origin. The Ru-II site is inaccessible to CO in the bridged complex, (II,III)(b). [(RuRuIII)-Ru-II(OH)(ttha)](2-) is a unique example of a M(II)XM(III) bridged complex of the iron group which exists in solution without secondary, rigid bridging ligands such as carboxylate and phosphate ions, in addition to the X bridge toro or hydroxo), enforcing the stability of the M(II)M(III) species; all known prior examples dissociate into monomeric complexes. However, the proximity of the binuclear centers which is afforded by the ttha(6-) ligand with a central ethylene bridge between two metal ion sites facilitates formation of (RuORuIII)-O-III, (RuORuIV)-O-III, and Ru-II(OH)Ru-III entities without additional inflexible metal-bridging ligand attachments, typical of mu-oxo-bis(mu-carboxylate) bridging. Electrochemical methods have been used to measure a comproportionation constant, K-c’, for the reddish-purple (II,III) complex equal to 18, indicative of a delocalization energy of less than 1.7 kcal/mol and a type II mixed-valence species. Oxidation of (II,III) by Ce-IV, O-2, or H2O2 yields a metastable golden yellow-brown (III,III)(b) species. (III,III)(b) has an oxo-bridged structure which aquates into the extended chain structure (III,III)(o) that appears straw yellow (k = 2.50 x 10(-3) s(-1)). Prolonged air oxidation of (III,III)(o) generates the ore-bridged (III,IV) complex with virtually identical spectral properties of the known [(RuORuIV)-O-III(edta)(2)](3-) complex. A band at 620 nm (epsilon/Ru = 1.18 X 10(3) M(-1) cm(-1)) imparts the characteristic green color to the type III mixed-valence (III,IV) complex. The (III,IV) complex exhibits an enhanced IR band at 877 cm(-1) similar to a band at 870 cm(-1) for the [(RuORuIV)-O-III(edta)(2)](3-) analogue. Oxidation of (III,IV) to (IV,IV) occurs at 1.20 V vs NHE while the (III,IV) to (III,III)(b) reduction appears at 1.14 V. An oxidation wave for the (III,III)(o) --> (III,IV)(b) process was identified at 0.83 V.