title: Solvent control on the selective, nonselective, and absent response of a partially substituted lower rim calix(4)arene derivative for soft metal cations (mercury(II) and silver(I)). Structural and thermodynamic studies.
abstract: The solvent control on the ability of a partially substituted lower rim calix(4)arene derivative 5,11,17,23,tetra-tert-butyl[25,27-bis(hydroxy)-26,28-bis(ethylthioethoxy)]-calix(4)arene, 1 to host soft metal cations (Hg(II) and Ag(I)) is demonstrated through 1H NMR, electrochemical (conductance measurements), and thermodynamic characterization of the complexation process in a wide variety of solvents. Solvent-ligand interactions were assessed from 1H NMR measurements involving 1 and various solvents in CDCl3. Thus, the formation of a 1:1 1-CH3CN adduct is reported. As far as metal cations are concerned, depending on the medium their complexation with 1 was only observed for Hg(II) and Ag(I). Thus, in acetonitrile, 1 is more selective for Hg(II) relative to Ag(I) by a factor of 2.2 x 10(3). In methanol the selectivity is reversed to an extent that the affinity of 1 for Ag(I) is 1.4 x 10(3) higher than that for Hg(II). However, 1 is unable to recognize selectively these cations in N,N-dimethylformamide while in propylene carbonate the ability of 1 to interact with these cations is lost. An outstanding feature of thermodynamics emerges when an assessment is made of the ligand effect on the complexation of these cations and analogues calix(4)arene derivatives. Thus, in acetonitrile the thermodynamics of cation complexation by the hydrophilic cavity of a calix(4)arene containing mixed pendant groups is built up from thermodynamic data for the same process involving derivatives with common functionalities at the narrow rim. This is a unique example of the additive contribution of pendant arms in the field of thermodynamics of calixarene chemistry.
authors.affiliation: Laboratory of Thermochemistry, Department of Chemistry, University of Surrey, Guildford, Surrey GU2 7XH, UK. a.danil-denamor@surrey.ac.uk
authors.forename: Angela F
authors.initials: AF
authors.lastname: Danil de Namor
authors.forename: Samir
authors.initials: S
authors.lastname: Chahine
authors.forename: Eduardo E
authors.initials: EE
authors.lastname: Castellano
authors.forename: Oscar E
authors.initials: OE
authors.lastname: Piro
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D047250:Calixarenes / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008628:Mercury / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry; D010636:Phenols / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000097:Acetonitriles; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D012997:Solvents; C121325:calix(4)arene; D047250:Calixarenes; D012834:Silver; D008628:Mercury; D000432:Methanol; C032159:acetonitrile