Amendola Valeria, Boiocchi Massimo, Fabbrizzi Luigi, Palchetti Arianna
Dipartimento di Chimica Generale, Università di Pavia, viale Taramelli 12, 27100 Pavia, Italy.
Chemistry. 2005 Sep 19;11(19):5648-60. doi: 10.1002/chem.200500351.
The trifurcate receptor 1(3+) forms stable 1:1 complexes with halide and oxo anions in MeCN solution, as shown by spectrophotometric and 1H NMR experiments, and selectively recognizes chloride (lg K(ass) > 7) in the presence of fluoride and bromide. The high stability reflects the receptor's ability to donate up to six hydrogen bonds (from three pyrrole N-H and three C-H fragments, polarized by the proximate positive charge) to the included anion. Addition of an excess of more basic anions (F- and CH3COO-) induces stepwise deprotonation of the N-H groups, an event signalled by the appearance of a bright yellow color. Crystal and molecular structures are reported for the complex with NO3(-) and a capsule consisting of two interconnected trifurcate subunits, one of which includes an H-bound Br- ion, while the other is doubly deprotonated and includes an H-bound water molecule. Finally, evidence is given for the formation in solution of an authentic complex of OH-, in which H-bound hydroxide is included within the cavity of 1(3+).
