Kinetically controlled self-assembly of Rh(II)-based squares assisted by monotopic ligand

Self-assembled coordination squares consisting of cis-protected dinuclear Rh(II) corner complexes and linear ditopic ligands were selectively produced in solution under kinetic control with the assistance of a weak monotopic carboxylate ligand (2,6-dichlorobenzoate: dcb–) as a leaving ligand. Preventing the cyclization step in the triangular formation by the leaving ligand enabled to produce the molecular square only. It was also found that dcb– can selectively convert the triangular complex into the square complex at room temperature, though heating at 373 K for 2 days is needed for the conversion without dcb– and that DMSO blocked the transformation process with dcb–. These results indicate that the energy landscape of the Rh(II)-based molecular self-assembly can be modulated properly by monotopic carboxylate ligand and solvent so that the self-assembly proceeds under kinetic control. Furthermore, one of the molecular squares assembled into a dimeric structure by the solvophobic effect, whose structure was characterized by NMR spectroscopy and single-crystal X-ray analysis.