This work describes the synthesis and characterization of mononuclear and dinuclear Ru(II) and Os(II) complexes based on the symmetrical bridging ligand isoeilatin (1). The crystal structure of 1 center dot[HCl](2) consists of layers of tightly pi-stacked molecules of the biprotonated isoeilatin. The mononuclear complexes [Ru(bpy)(2)(ieil)](2+) (2(2+)) and [Os-(bpy)2(ieil)](2+) (3(2+)) form discrete dimers in solution held together by face-selective T-stacking interactions via the isoeilatin ligand. Coordination of a second metal fragment does not hinder the pi-stacking completely, as demonstrated by the concentration dependence of the H-1 NMR spectra of the dinuclear complexes [{Ru(bpy)(2)}(2){mu-iei}](4+) (4(4+)), [{Os(bpy)(2)}(2){mu-ieil](4+) (5(4+)), and [{Ru(bpy)(2)}{mu-ieil}{Os(bpy)(2)}](4+) (6(4+)) and supported by the solid-state structure of meso-4 center dot[Cl](4). The bridging isoeilatin ligand conserves its planarity even upon coordination of a second metal fragment, as demonstrated in the solid-state structures of meso-4 center dot[Cl](4), meso-4 center dot[PF6](4), and meso-5 center dot[PF6](4). All of the dinuclear complexes exhibit a preference (3/2-3/1) for the formation of the heterochiral as opposed to the homochiral diastereoisomer. Absorption spectra of the mononuclear complexes feature a low-lying d(pi)(M) -> pi*-(ieil) MLCT band around 600 nm that shifts to beyond 700 nm upon coordination of a second metal fragment. Cyclic and square-wave voltammetry measurements of the complexes exhibit two isoeilatin-based reduction waves that are substantially anodically shifted compared to [M(bpy)(3)](2+) (M = Ru, Os). Luminescence spectra, quantum yields, and lifetime measurements at room temperature and at 77 K demonstrate that the complexes exhibit (MLCT)-M-3 emission that occurs in the IR region between 950 and 1300 nm. Both the electrochemical and photophysical data are consistent with the low-lying pi* orbital of the isoeilatin ligand. The dinuclear complexes exhibit two reversible, well-resolved, metal-centered oxidation waves, despite the chemical equivalence of the two metal centers, indicating a significant metal-metal interaction mediated by the bridging isoeilatin ligand.