title: Effective concentration as a tool for quantitatively addressing preorganization in multicomponent assemblies: application to the selective complexation of lanthanide cations.
abstract: The beneficial entropic effect, which may be expected from the connection of three tridentate binding units to a strain-free covalent tripod for complexing nine-coordinate cations (Mz+ = Ca2+, La3+, Eu3+, Lu3+), is quantitatively analyzed by using a simple thermodynamic additive model. The switch from pure intermolecular binding processes, characterizing the formation of the triple-helical complexes [M(L2)3]z+, to a combination of inter- and intramolecular complexation events in [M(L8)]z+ shows that the ideal structural fit observed in [M(L8)]z+ indeed masks large energetic constraints. This limitation is evidenced by the faint effective concentrations, ceff, which control the intramolecular ring-closing reactions operating in [M(L8)]z+. This predominence of the thermodynamic approach over the usual structural analysis agrees with the hierarchical relationships linking energetics and structures. Its simple estimation by using a single microscopic parameter, ceff, opens novel perspectives for the molecular tuning of specific receptors for the recognition of large cations, a crucial point for the programming of heterometallic f-f complexes under thermodynamic control.
authors.affiliation: Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Canard
authors.forename: Sylvain
authors.initials: S
authors.lastname: Koeller
authors.forename: Gérald
authors.initials: G
authors.lastname: Bernardinelli
authors.forename: Claude
authors.initials: C
authors.lastname: Piguet
mesh_terms: D002412:Cations / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D002412:Cations; D028581:Lanthanoid Series Elements