Two multisite 5,5'-disubstituted 2,2'-bipyridine ligands containing N-methyl hydroxamic acids as substituents [5,5'-bis(N-methylhydroxamic)-2,2'-bipyridine (4) and 5-methyl-5'-(N-methylhydroxamic)-2,2-bipyridine (10)] were synthesized. These ligands were used in order to illustrate the strategy of self-assembly through sequential complexation. According to this concept, the first metal added organizes the ligands disposed in 5,5'-positions to accomodate the second metal ion that is sequentially added. Thus, addition of Fe2+ to a solution of 4 led to a Fe2+-tris(bipyridine) complex. Addition of Fe3+ to this solution yielded a trimetallic architecture, which was characterized. Ligand 10 yielded a mixture of bimetallic architectures through complexation with Fe2+ followed by Fe3+ ions. However, if the order of metal addition is changed, only one bimetallic complex is obtained. This is due to the fact that the first metal ion added (Fe3+) acts as a template, organizing the bipyridine ligands and preforming an adequate cavity for the Fe2+ ion.
inorganic self-assembly; sequential ligands; sequential complexation; metallo-exoreceptors
