Synthesis and Anion Sensing of Water-Soluble Metallomacrocycles

The self-assembly of (TMEDA)Pd(NO3)2 or (TMEDA)Pt(NO3)2 (where TMEDA = N1,N1,N2,N2-tetramethylethane-1,2-diamine) and anthracene- or ferrocene-based diimidazole ligands (L1–3) in aqueous solution affords a series of positively charged [M2L2]4+ dimetallomacrocycles. Their structures were characterized by 1H NMR and electrospray ionization mass spectrometry and in the cases of {[(TMEDA)Pd]2L12}(NO3)4 (1), {[(TMEDA)Pd]2L12}(PF6)4 (1a), and {[(TMEDA)Pd]2L32}(NO3)4 (4) by single-crystal X-ray diffraction analysis. Interestingly, the NMR spectra of 1 and 1a revealed that the difference of their structures, as confirmed by X-ray diffraction analysis, was that a NO3– of 1 was encapsulated inside the cavity of the basket-shaped metallomacrocycle by C–H···O hydrogen bonds, while PF6– of 1a was bound outside by C–H···F hydrogen bonds. The fluorescence titration experiment exhibited the formation of 1:1 host–guest complexation for anthracene-based positively charged [M2L2]4+-type metallomacrocycles with NO3–. The interactions between metallomacrocycles and various anions were investigated via fluorescence titration and cyclic voltammetry studies, respectively.