A "ter-ionic complex" composed of a tetracationic Ru(II) complex and two iodide ions was found to yield a covalent I-I bond upon visible light excitation in acetone solution. H-1 NMR, visible absorption and DFT studies revealed that one iodide was associated with a ligand while the other was closer to the Ru metal center. Standard Stern-Volmer quenching of the excited state by iodide revealed upward curvature with a novel saturation at high concentrations. The data were fully consistent with a mechanism in which the Ru metal center in the excited state accepts an electron from iodide to form an iodine atom and, within 70 ns, that atom reacts with the iodide associated with the ligand to yield I-2(center dot-). This rapid formation of an I-I bond was facilitated by the supramolecular assembly of the three reactant ions necessary for this ter-ionic reaction that is relevant to solar fuel production.