Self-Assembly of 2D and 3D Metallo-Supramolecules with Increasing Complexity

Synthetic organic chemistry played a crucial role in the construction of molecules through the formation and dissociation of covalent bonds. However, the laborious synthetic procedures as well as the low yield after multiple steps have restricted the pursuit of complicated giant molecules with high efficiency. Being complementary to organic synthesis, self-assembly provided an alternative route to achieving the giant architectures using weak non-covalent interactions in high efficiency, which is in analog to natural systems such as DNA, peptide, and protein. Among the various interactions, coordination has shown unique advantages in terms of directionality, reversibility and strength. Serving as a bottom-up approach, coordination-driven self-assembly has been well flourished in the past few decades and is ready to face more challenges in constructing complicated 2D and 3D architectures with increasing complexity. Pyridine is one of the most important ligands that have been extensively applied in the self-assembly of metallo-supramolecules. i.e., the coordination with square-planner metal centers to generate 2D and 3D architectures. Inspired by the beauty of Star of David, we have designed and synthesized 2D and 3D star-shaped metallo-supramolecules with Star of David figures via the self-assembly of tetratopic pryidinyl ligand with 180° diplatinum(II) motif and Pd(II), respectively. Compared with other strategies such as template-directed synthesis and stepwise self-assembly, this design allows the formation of 2D and 3D structures in one step with nearly quantitative yield. The structures were characterized via both one-dimensional (1H, 13C, 31P) and two-dimensional (COSY, NOESY, DOSY) NMR techniques, as well as electrospray ionization-mass spectrometry (ESI-MS) and ion mobility-mass spectrometry (IM-MS), AFM, TEM as well as X-ray crystallography. Moreover, the stabilities of the 2D and 3D structures were measured and compared using gradient tandem-mass spectrometry (gMS2). The high stability of 3D Star of David was correlated to its high density of coordination sites (DOCS). Being a derivative of pyridine, terpyridine as a tridentate ligand has also been widely applied in the coordination with transition metal ions to construct metallo-macrocycles and metallo-cages. Challenges still remain, however, within the construction of giant architectures in terms of high efficiency and complexity from simple building blocks. Inspired by the features of DNA and protein, which both have specific sequence, we designed a series of linear building blocks with specific sequences through the coordination between terpyridine ligands and Ru(II). Different generations of polycyclic supramolecules (C1 to C5) with increasing complexity are obtained through the self-assembly with Cd(II), Fe(II) or Zn(II). The assembled structures are characterized via multi-dimensional mass spectrometry analysis as well as multi-dimensional and multi-nuclear NMR (1H, COSY, NOESY, 19F) analysis. Moreover, the largest two cycles C4 and C5 hierarchically assemble into ordered nanoscale structures on a graphite based on their precisely-controlled shapes and sizes with high shape-persistence