Iron(III) complexation behavior of benzene-centered tripodal mono-, di- and tritopic ligands carrying a repeating -Ahe-(HO)Apr- sequence [Ahe=6-aminohexanoyl; (HO)Apr=3-(N-hydroxy)aminopropanoyl]

To investigate how three-directional molecules behave upon complexation wit h ferric iron, tripodal 1,3,5-benzene-centered mono-, di- and tritopic iron -chelating ligands {C6H3[CO-(Ahe-(HO)Apr)(n)-OH](3): 1, n=1; 2, n=2; 3, n=3 }, composed of strands containing an -Ahe-(HO)Apr- sequence [Ahe=6-aminohex anoyl; (HO)Apr=3-(N-hydroxy)aminopropanoyl], were synthesized. These hydrox amate ligands form intramolecular six-coordinate octahedral complexes with Fe(iii): Fe-1-1, Fe-1-2, Fe-2-2, Fe-1-3, Fe-2-3 and Fe-3-3. The complexes f ormed were investigated from a topological viewpoint and examined in terms of stability against attack by H+ and HO-, monoprotonation equilibrium and iron removal kinetics using a 20-molar excess of EDTA. Fe-1-1, Fe-1-2 and F e-2-2 have tripodal interstrand structures. In particular, the iron removal reaction of Fe-2-2 shows a consecutive first-order reaction pattern. From kinetic data of the first-order reactions, Fe-1-3, Fe-2-3 and Fe-3-3 are co ncluded to possess one, two and three discrete ferrioxamine-type (intrastra nd) structures, respectively.