Texaphyrin complexes having improved functionalization

Texaphyrin metal complexes having improved functionalization include the addition of electron-donating groups to positions 2, 7, 12, 15, 18 and/or 21 and/or the addition of electron-withdrawing groups to positions 15 and/or 18 of the macrocycle. Electron-donating groups at positions 2, 7, 12, 15, 18 and/or 21 contribute electrons to the aromatic .pi. system of the macrocycle which stabilizes the metal complex to demetallation and the imine bonds to hydrolysis. These texaphyrin metal complexes having enhanced stability are useful for localization, radiosensitization and radiation therapy. Electron-withdrawing groups at positions 15 and/or 18 render the macrocycle more readily reduced, i.e. the redox potential is lower and the macrocycle more readily gains an electron to form a radical. Such texaphyrins having a low redox potential are useful for radiation sensitization applications.