An improved synthesis of 3, 6-diformylpyridazine I has been elaborated. The macrocyclic complexes Pb2L1 (ClO4) 41 and [Pb2L2][ClO4] 42 were prepared from this precursor, 1, 3- diaminopropane and lead (II) perchlorate in 1: 1: 1 and 2: 2: 1 ratios respectively. The ability of lead (II) perchlorate to template the formation of the two macrocycle ring sizes, L1=(2+ 2) and L2=(4+ 4), simply by alteration of the reagent ratio is unprecedented. Transmetallation ...