A series of ruthenium(II) diimine complexes containing thia-, selena-and aza-crowns derived from 1,10-phenanthroline have been synthesized and characterized, and their photophysics and electrochemistry were studied. Their interaction with metal ions was investigated by UV-vis, luminescence, and H-1 NMR spectroscopy. The crystal structures of [Ru(bpy)(2)(L1)](PF6)(2), [Ru(bpy)(2)(L2)](ClO4)(2), [Ru(bpy)(2)(L3)](ClO4)(2), and [Ru(bpy)(2)(L4)](ClO4)(2) have been determined. The luminescence properties of [Ru(bpy)(2)(L1)](ClO4)(2) were found to be sensitive and selective toward the presence of Hg2+ ions in an acetonitrile solution. The addition of alkaline-earth metal ions, Zn2+, Cd2+, and Hg2+ ions, to the solution of [Ru(bpy)(2)(L6)](ClO4)(2) in acetonitrile gave rise to large changes in the UV-vis and emission spectra. The binding of metal ions to [Ru(bpy)(2)(L6)](ClO4)(2) was found to cause a strong enhancement in the emission intensities of the complex, with high specificity toward Hg2+ ions.