The reactive ligand 1,10-phenanthroline-5,6-epoxide is a versatile starting material for the preparation of a variety of 5-substituted-1, 10-phenanthroline ligands by reaction with oxygen-, carbon-, or nitrogen-based nucleophiles. All of the new ligands readily form complexes with the fac-Re-1(CO)(3)Cl fragment. Of particular interest are the syntheses of the amino and aminocrown derivatives of Re-1 which can function as cation sensors by perturbation of molecular luminescence. An interesting example involving Pb2+ is presented.