title: A polyaromatic terdentate binding unit with fused 5,6-membered chelates for complexing s-, p-, d-, and f-block cations.
abstract: The polyaromatic terdentate ligand 6-(azaindol-1-yl)-2,2′-bipyridine (L7) combines one 5-membered chelate ring with a fused 6-membered chelate ring. It is designed to provide complexation properties intermediate between 2,2′;6′,2″-terpyridine (L1) (two fused 5-membered chelate rings) and 2,6-bis(azaindol-1-yl)pyridine (L6) (two fused 6-membered chelate rings). In polar organic solvents, L7 displays remarkable affinities for the successive fixation of two small univalent cations M = H+ or Li+, leading to stable [M(m)(L7)]m+ (m = 1–2) complexes. Upon reaction with M = Mg2+ or Zn2+ cations, the large positive charge densities borne by the metals result in the successive cooperative complexation of two ligands to give [M(L7)n]n+ (n = 1–2). For small Sc3+, unavoidable traces of water favor the formation of the protonated ligand at millimolar concentrations in acetonitrile, but the use of larger Y3+ cations leads to [Y(L7)n]n+ (n = 1, 2), for which stability constants of log(β(1,1)(Y,L7)) = 2.9(5) and log(β(1,2)(Y,L7)) = 5.3(4) are estimated. The complexation behaviors are supported by speciations in solution, thermodynamic analyses, and solution and solid-state structures.
authors.affiliation: Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, 30 quai E. Ansermet, CH-1211 Geneva 4, Switzerland. Thi.Hoang@unige.ch
authors.forename: Thi Nhu Y
authors.initials: TN
authors.lastname: Hoang
authors.forename: Marie
authors.initials: M
authors.lastname: Humbert-Droz
authors.forename: Thibault
authors.initials: T
authors.lastname: Dutronc
authors.forename: Laure
authors.initials: L
authors.lastname: Guénée
authors.forename: Céline
authors.initials: C
authors.lastname: Besnard
authors.forename: Claude
authors.initials: C
authors.lastname: Piguet