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What Anions Do Inside a Receptor's Cavity: A Trifurcate Anion Receptor Providing Both Electrostatic and Hydrogen‐Bonding Interactions
Author(s) -
Amendola Valeria,
Boiocchi Massimo,
Fabbrizzi Luigi,
Palchetti Arianna
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500351
Subject(s) - deprotonation , chemistry , hydrogen bond , bromide , halide , crystallography , pyrrole , molecule , ion , chloride , hydroxide , inorganic chemistry , stereochemistry , medicinal chemistry , organic chemistry
The trifurcate receptor 1 3+ forms stable 1:1 complexes with halide and oxo anions in MeCN solution, as shown by spectrophotometric and 1 H 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 NH and three CH fragments, polarized by the proximate positive charge) to the included anion. Addition of an excess of more basic anions (F − and CH 3 COO − ) induces stepwise deprotonation of the NH groups, an event signalled by the appearance of a bright yellow color. Crystal and molecular structures are reported for the complex with NO 3 − 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+ .