title: Allosteric effects in binuclear homo- and heterometallic triple-stranded lanthanide podates.
abstract: This work illustrates a simple approach for deciphering and exploiting the various free energy contributions to the global complexation process leading to the binuclear triple-stranded podates [Ln(2)(L9)](6+) (Ln is a trivalent lanthanide). Despite the larger microscopic affinities exhibited by the binding sites for small Ln(3+), the stability constants measured for [Ln(2)(L9)](6+) decrease along the lanthanide series; a phenomenon which can be ascribed to the severe enthalpic penalty accompanying the intramolecular cyclization around small Ln(III), combined with increasing anticooperative allosteric interligand interactions. Altogether, the microscopic thermodynamic characteristics predict β(1,1,1)(La,Lu,L9)/β(1,1,1)(Lu,La,L9) = 145 for the ratio of the formation constants of the target heterobimetallic [LaLu(L9)](6+) and [LuLa(L9)](6+) microspecies, a value in line with the quantitative preparation (>90%) of [LaLu(L9)](6+) at millimolar concentrations. Preliminary NMR titrations indeed confirm the rare thermodynamic programming of a pure heterometallic f-f' complex.
authors.affiliation: Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland.
authors.forename: Patrick E
authors.initials: PE
authors.lastname: Ryan
authors.forename: Gabriel
authors.initials: G
authors.lastname: Canard
authors.forename: Sylvain
authors.initials: S
authors.lastname: Koeller
authors.forename: Bernard
authors.initials: B
authors.lastname: Bocquet
authors.forename: Claude
authors.initials: C
authors.lastname: Piguet