Selective Self-Assembly of a Rectangular Ruthenium Supramolecule from an Unsymmetrical Bridging Unit.

Herein, we report the synthesis of an unsymmetrical diruthenium bridging unit containing a multidentate oxamate ligand and the subsequent formation of a rectangular supramolecule. The reaction of oxamate 1, 2-((4-bromo-2,6-dimethylphenyl)amino)-2-oxo-acetic acid, and [(p-cymene)RuCl2]2 affords a novel unsymmetrical diruthenium acceptor clip 2, where two ruthenium metal centers are ligated with either [O,O] or [N,O]. The molecular clip 2 and bipyridine donor self-assemble to form two-dimensional rectangular supramolecule 3. Self-assembly can produce seven possible isomers depending on the position of the substituted bromoaryl groups. However, 1H NMR spectroscopic investigation indicated only two different isomers in the reaction mixture. A single isomer is isolated via crystallization, and X-ray crystallography confirms that the product is a C1 symmetric two-dimensional rectangular supramolecule, in which two bromoaryl groups are located in the farthest position from each other. Theoretical calculations suggest that the self-assembly of supramolecule 3 occurred via 1:1 adducts of the diruthenium molecular clip and bipyridine as an intermediate to predominantly form a single isomer.

Unique Ruthenium Bimetallic Supramolecular Cages From C4-Symmetric Tetrapyridyl Metalloligands.

The self-assembly of C4-symmetric tetrapyridyl metalloligands containing Fe or Co and diruthenium electron acceptors by means of dative coordination bonding led to the formation of six different heterobimetallic supramolecules. All complexes were characterized by X-ray crystallography, ESI mass spectrometry, and 1H NMR (in the case of diamagnetic systems) spectroscopy. The bridging units in the diruthenium complexes greatly influenced the geometrical preference of the supramolecular structures, resulting in the formation of different architectures, namely A4D2 or A6D3 (A = acceptor, D = donor). Depending on the bridging unit, A4D2 tetragonal prism, A4D2 molecular tweezer, or A6D3 triple-decker complexes were obtained selectively. The self-assembly of an unexpected triple-decker type Ru12Fe3 heterobimetallic species was also observed.