Self-assembly of a Pd-based molecular bowl as anion receptor featured by multiple C[sbnd]H···anion hydrogen bonds

Abstract

The self-assembly of (tmen)Pd(NO3)2 (where tmen = N1, N1, N2, N2-tetramethylethane-1,2-diamine) and 4,7-phenanthroline rigid ligand (L) in aqueous solution affords positively charged [Pd3L3]6+ Pd-based molecular bowls (1a·6NO3− and 1b·6BF4−). Their structures were characterized by 1H NMR, electrospray ionization mass spectrometry and single-crystal X-ray diffraction analysis. Interestingly, X-ray diffraction analysis of 1a·6NO3− and 1b·6BF4− revealed that an anion was bound inside the cavity of the bowl-shaped structure by multiple CH···O hydrogen bonds in 1a·6NO3−, while multiple CH···F hydrogen bonds in 1b·6BF4−. The interactions between [Pd3L3]6+ molecular bowl and a variety of anions were investigated via NMR titration and fluorescent studies, respectively.