title: Synthesis, structures, and conformational characteristics of calixarene monoanions and dianions.
abstract: The synthesis, complete characterization, and solid state structural and solution conformation determination of calix[n]arenes (n = 4, 6, 8) is reported. A complete series of X-ray structures of the alkali metal salts of calix[4]arene (HC4) illustrate the great influence of the alkali metal ion on the solid state structure of calixanions (e.g., the Li salt of monoanionic HC4 is a monomer; the Na salt of monoanionic HC4 forms a dimer; and the K, Rb, and Cs salts exist in polymeric forms). Solution NMR spectra of alkali metal salts of monoanionic calix[4]arenes indicate that they have the cone conformation in solution. Variable-temperature NMR spectra of salts HC4.M (M = Li, Na, K, Rb, Cs) show that they possess similar coalescence temperatures, all higher than that of HC4. Due to steric hindrance from tert-butyl groups in the para position of p-tert-butylcalix[4]arene (Bu(t)C4), the alkali metal salts of monoanionic Bu(t)C4 exist in monomeric or dimeric form in the solid state. Calix[6]arene (HC6) and p-tert-butylcalix[6]arene (Bu(t)C6) were treated with a 2:1 molar ratio of M(2)CO(3) (M = K, Rb, Cs) or a 1:1 molar ratio of MOC(CH(3))(3) (M = Li, Na) to give calix[6]arene monoanions, but calix[6]arenes react in a 1:1 molar ratio with M(2)CO(3) (M = K, Rb, Cs) to afford calix[6]arene dianions. Calix[8]arene (HC8) and p-tert-butylcalix[8]arene (Bu(t)()C8) have similar reactivity. The alkali metal salts of monoanionic calix[6]arenes are more conformationally flexible than the alkali metal salts of dianionic calix[6]arenes, which has been shown by their solution NMR spectra. X-ray crystal structures of HC6.Li and HC6.Cs indicate that the size of the alkali metal has some influence on the conformation of calixanions; for example, HC6.Li has a cone-like conformation, and HC6.Cs has a 1,2,3-alternate conformation. The calix[6]arene dianions show roughly the same structural architecture, and the salts tend to form polymeric chains. For most calixarene salts cation-pi arene interactions were observed.
authors.affiliation: Department of Chemistry, Texas Christian University, Box 298860, Fort Worth 76129, USA. t.hanna@tcu.edu
authors.forename: Tracy A
authors.initials: TA
authors.lastname: Hanna
authors.forename: Lihua
authors.initials: L
authors.lastname: Liu
authors.forename: Alfredo M
authors.initials: AM
authors.lastname: Angeles-Boza
authors.forename: Xiaodi
authors.initials: X
authors.lastname: Kou
authors.forename: C David
authors.initials: CD
authors.lastname: Gutsche
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Ejsmont
authors.forename: William H
authors.initials: WH
authors.lastname: Watson
authors.forename: Lev N
authors.initials: LN
authors.lastname: Zakharov
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Incarvito
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold