Rapid Metal Ions Shuttling through 1,3-Alternate Thiacalixcrown Tubes
journal contributionposted on 26.07.2003, 00:00 by Jae Kwang Lee, Sung Kuk Kim, Richard A. Bartsch, Jacques Vicens, Sotaro Miyano, Jong Seung Kim
Several new thiacalixmonocrown and thiacalixbiscrown compounds were synthesized. Their metal ion extractabilities are found to be lower than those of conventional calixcrowns. By use of X-ray crystal structures and 1H NMR spectroscopy, this result is explained by weaker electrostatic interactions of the polyether ring oxygen atoms with the metal ions and diminished π-metal ion interactions between the metal ions and the aromatic rings of the thiacalixcrowns. Temperature-dependent 1H NMR spectroscopic measurements reveal coalescence temperatures Tcintra and Tcinter for metal ion exchange. In one case, this exchange was rationalized as metal ion shuttling through a thiacalixbiscrown tube. Since the metal ions are less tightly complexed by the polyether units in thiacalixbiscrowns than in conventional calixbiscrowns, more facile metal ion exchange between the two polyether units takes place in the former.