Preorganization is important in the recognition of metal ions by ligands. A ligand is more
preorganized the more it is constrained as the free ligand to be in the conformation required to
complex the target metal ion. Until the present time, high levels of preorganization have been
achieved by cyclization of open-chain ligands to yield macrocycles and cryptands. A novel
approach to designing highly preorganized ligands is followed where high levels of
preorganization are achieved using the rigid 1,10-phenanthroline (1,10-phen) delocalized system
as the backbone of the ligand. The highly preorganized ligands 1,10-phenanthroline-2,9-
dialdoxime (PDOX) and bis-1,10-phenanthroline (DIPHEN) and their complexing properties
with various metal ions have been studied.PDOX was synthesized by a literature method. Column chromatography of the product obtained
by this method gave a product of improved purity, as shown by NMR and IR, and a considerably
higher melting point. UV/VIS spectrometry was used in titrations to determine protonation
constants of the free ligands and their stability constants with metal ions. Stability constants,
logK1, for PDOX and DIPHEN with Ca(II), Cd(II), Cu(II), Gd(III), Pb(II), and Zn(II) have been
determined. Fluorescence properties of PDOX and Ca(II), Cd(II), Pb(II), Hg(II), and Zn(II) were
examined. The strong chelation enhanced fluorescence (CHEF) effect found with PDOX and
metal ions such as Cd(II) and Pb(II) suggest that these ligands will have potential applications in
biology, and in the development of sensors for these metal ions in the environment
