The reaction of 2,9-di(pyrid-2'-yl)-1,10-phenanthroline (dpp) with [RuCl3 center dot 3H(2)O] or [Ru(DMSO)(4)Cl-2] provides the reagent trans-[Ru-II(dpp)Cl-2] in yields of 98 and 89%, respectively. This reagent reacts with monodentate ligands L to replace the two axial chlorides, affording reasonable yields of a ruthenium(II) complex with dpp bound tetradentate in the equatorial plane. The photophysical and electrochemical properties of the tetradentate complexes are strongly influenced by the axial ligands with electron-donating character to stabilize the ruthenium(III) state, shifting the metal-to-ligand charge-transfer absorption to lower energy and decreasing the oxidation potential. When the precursor trans-[Ru-II(dpp)Cl-2] reacts with a bidentate (2,2'-bipyridine), tridentate (2,2';6,2 ''-terpyridine), or tetradentate (itself) ligand, a peripheral pyridine on dpp is displaced such that dpp binds as a tridentate. This situation is illustrated by an X-ray analysis of [Ru(dpp)(bpy)Cl](PF6).