Syntheses, properties, and reactions of hydroxido- or oxido-bridged dinuclear ruthenium complexes bearing a tridentate auxiliary ligand, ethylbis(2-pyridylmethyl)amine (ebpma) or benzylbis(2-pyridylmethyl)amine (bbpma), have been investigated. Reduction reactions of a singly oxidobridged diruthenium complex bearing ebpma, [{(RuCl2)-Cl-III,IV(ebpma)}(2)(mu-O)](+) ([2(Cl)](+)), by zinc in acetonitrile afforded an acetonitrile-substituted singly oxido-bridged complex in the Ru-III-Ru-III isovalent state, [{(RuCl)-Cl-III,III(NCCH3)(ebpma)}(2)(mu-O)](2+) ([2(CH3CN)](2+)]. Chlorido ligand abstraction reactions using silver salts have also been attempted. Through a reaction of [2Cl](+) with two equimolar amounts of AgNO3 in water-acetone, a singly oxido-bridged complex having an aqua and a hydroxido, [{(RuCl)-Cl-III(OH2)(ebpma)}(mu-O){(RuCl)-Cl-IV-(OH)(ebpma)}](2+) ([2(H2O-OH)](2+)), was obtained. Reactions with four equimolar amounts of AgL (L = CH3COO- or NO3-) in water-acetone gave doubly oxido- and bidentate oxygen donor ligand-bridged diruthenium complexes of Ru(III)-Ru(IV), [{Ru-III,Ru-IV(ebpma)}(2)(mu-O)(2)(mu-L)](2+) ([3(L)](2+); L = O2CCH3; [3(CH3COO)](2+), L = O2NO; [3(NO3)](2+)). Reactions of [3(L)](2+) under acidic conditions afforded a corresponding one-protonated species having the {Ru-2(mu-O)(mu-OH)} core. Reactivity and electronic structure of the oxido-bridged diruthenium complexes were studied by electrochemical, spectroscopic, and theoretical methods.