The complexes (OC) 3 ClRe(abpy) (1) and [(OC) 3 ClRe] 2 (abpy) (2) with abpy=2,2'-azobispyridine were structurally characterized and studied by spectroelectrochemistry in the UV-vis and in the IR carbonyl stretching region. Compound 1 exhibits a s-cis/E/s-trans configurated abpy ligand with metal coordination to one pyridyl and one azo function and one non-bonding Re N interaction at 3.293 9 to the second pyridyl nitrogen atom. The dinuclear complex 2 with two azoimine-coordinated metal centers is distinguished by the trans arrangement of the chloride ligands with respect to the Re 2 (μ-abpy) plane, the Re Re distance is 5.033(7) 9. The azo bond lengths at 1.272(9) (1) and 1.304(10) 9 (2) indicate substantial π back donation from the rhenium(I) centers into the π*(abpy) orbital. Spectroelectrochemistry reveals the successive occupation of the π*(abpy) orbital by electrons; metal-to-ligand charge transfer features are shifted to higher energies and carbonyl stretching bands to lower wavenumbers. The EPR spectra of both radical anion intermediates 1 - and 2 - are dominated by very similar 1 8 5 , 1 8 7 Re hyperfine splitting, ruling out a mixed-valent formulation. The second electron uptake is followed by the rapid loss of one chloride, leading to an unsymmetrical species in the dinuclear system.