Supramolecular self-assembly of homo- and hetero-leptic metal complexes using dipyrromethene ligands

Dipyrromethenes (dipyrrins) have been widely studied as important precursors for the synthesis of porphyrins for decades. More recently, bisdipyrrins, constructed through the controlled linkage of two dipyrrins, have drawn considerable attention in the field of supramolecular chemistry where supramolecular structures have exhibited potential application in the areas of gas storage and separation, catalysis and drug delivery. Bisdipyrrin metal complexes featuring double-, triple-helical or triangular structures have been previously reported by our group. The primary goal of this project was to synthesize new bisdipyrrin ligands to explore their applicability to the construction of novel homoleptic and heteroleptic metal complexes, such as circular helicates, grids, racks and ladders. The key to the successful synthesis of the homoleptic metal complexes (circular helicates and grids) is the spacer linking two dipyrrin units. Phenyldiacetylene and carbazolediacetylene were introduced to generate dinuclear circular helicates, whereas ligands with diacetylene as the spacer formed even higher nuclear oligomers. In the case of grids, the two central pyrrole rings were fused to a ring to allow the two dipyrrin units to be parallel to each other to eliminate unwanted circular helicates. Furthermore, both hexagons and grids are formed when phenyl groups were introduced to the dipyrrin ligands, and they show channel structures in their crystalline frameworks. Studies on driving forces such as π-π stacking and F-F interactions were conducted. A series of heteroleptic anti-parallel and parallel racks were prepared. Surprisingly, zigzag racks along with the parallel racks were generated without unwanted grids when the ligand with bulky phenyl groups was introduced. During the preparation of ladders, two heteroleptic metal complexes emerged that act as both the ligand and metal ion source. A Cu(II) rigid ladder and a Zn(II) flexible ladder were synthesized and characterized by X-ray diffraction analysis. Both ladders display rectangular channel structures in the solid state, which were guided by intermolecular CH/π and/or CH∙∙∙O interactions.Science, Faculty ofChemistry, Department ofGraduat