Coordination driven self-assembly of four new molecular boats using a flexible imidazole-containing donor linker

Abstract

Using a metal–ligand coordination bonding approach, the self-assembly of four new metallamacrocycles from Pd(II)-based 90° acceptors and a diimidazole donor ligand 1,3-bis(imidazole-1-ylmethyl)-2,4,6-trimethylbenzene (L) has been achieved. The assemblies are characterized fully by NMR and electrospray ionization-mass spectroscopic (ESI-MS) analysis and in two cases the X-ray single-crystal structure analysis established the gross structures. The selective formation of a diimidazole-based linker (L) containing macrocycle [(en)Pd(µ-L)₂Pd(en)]⁴⁺ from a 1 : 1 : 1 mixture of cis-Pd(en)(NO₃)₂, L and 1,2-bis(4-pyridyl)ethane is also established. Measuring the binding constants established the stronger Pd–L binding force compared to traditional Pd–N(pyridyl linker) interaction, which reveals the possibility of using imidazole donor ligands as potential linkers or even better ligands compared to the widely used pyridyl donor ligands in the construction of metal-based large supramolecular assemblies.