Palladium(II)-directed self-assembly of a neutral molecular triangle as a heteroditopic receptor for ion pairs

A molecular triangle, based on the self-assembly of 4,7-phenanthroline by a neutral palladium complex, has been synthesized and characterized by a combination of techniques: (1)H NMR and UV-vis absorption spectroscopies, mass spectrometry, elemental analysis, and gel permeation chromatography. This new neutral metallocavitand has demonstrated the capacity to host both anionic and cationic guests, thus acting as an open-shaped heteroditopic receptor. Density functional theory calculations have shown that (i) there is no overtension in the assembly of the discrete triangle, which is more stable than open-chain oligomers, (ii) the adducts formed between the triangle and some salts (modeled in the gas phase) are thermodynamically stable, and (iii) two types of cavities coexist in the triangle, which host ions and ion pairs. This easily accessible triangular unit extends further the rational design of model nanoarchitectures in host-guest chemistry with applications in analytical chemistry and multifunctional molecular materials.