title: Complexation of Ln(3+) Ions with Cyclam Dipicolinates: A Small Bridge that Makes Huge Differences in Structure, Equilibrium, and Kinetic Properties.
abstract: The coordination properties toward the lanthanide ions of two macrocyclic ligands based on a cyclam platform containing picolinate pendant arms have been investigated. The synthesis of the ligands was achieved by using the well-known bis-aminal chemistry. One of the cyclam derivatives (cb-tedpa(2-)) is reinforced with a cross-bridge unit, which results in exceptionally inert [Ln(cb-tedpa)](+) complexes. The X-ray structures of the [La(cb-tedpa)Cl], [Gd(cb-tedpa)](+), and [Lu(Me2tedpa)](+) complexes indicate octadentate binding of the ligands to the metal ions. The analysis of the Yb(3+)-induced shifts in [Yb(Me2tedpa)](+) indicates that this complex presents a solution structure very similar to that observed in the solid state for the Lu(3+) analogue. The X-ray structures of [La(H2Me2tedpa)2](3+) and [Yb(H2Me2tedpa)2](3+) complexes confirm the exocyclic coordination of the metal ions, which gives rise to coordination polymers with the metal coordination environment being fulfilled by oxygen atoms of the picolinate groups and water molecules. The X-ray structure of [Gd(Hcb-tedpa)2](+) also indicates exocyclic coordination that in this case results in a discrete structure with an eight-coordinated metal ion. The nonreinforced complexes [Ln(Me2tedpa)](+) were prepared and isolated as chloride salts in nonaqueous media. However, these complexes were found to undergo dissociation in aqueous solution, except in the case of the complexes with the smallest Ln(3+) ions (Ln(3+) = Yb(3+) and Lu(3+)). A DFT investigation shows that the increased stability of the [Ln(Me2tedpa)](+) complexes in solution across the lanthanide series is the result of an increased binding energy of the ligand due to the increased charge density of the Ln(3+) ion.
authors.affiliation: Grupo QUICOOR, Centro de Investigaciones Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Universidade da Coruña , Campus da Zapateira, Rúa da Fraga 10, 15008 A Coruña, Spain.|Université de Bretagne Occidentale, UMR-CNRS 6521, UFR des Sciences et Techniques , 6 avenue Victor le Gorgeu, C.S. 93837, 29238 Brest, Cedex 3, France.
authors.forename: Aurora
authors.initials: A
authors.lastname: Rodríguez-Rodríguez
authors.affiliation: Grupo QUICOOR, Centro de Investigaciones Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Universidade da Coruña , Campus da Zapateira, Rúa da Fraga 10, 15008 A Coruña, Spain.
authors.forename: Martín
authors.initials: M
authors.lastname: Regueiro-Figueroa
authors.affiliation: Grupo QUICOOR, Centro de Investigaciones Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Universidade da Coruña , Campus da Zapateira, Rúa da Fraga 10, 15008 A Coruña, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Esteban-Gómez
authors.affiliation: Université de Bretagne Occidentale, UMR-CNRS 6521, UFR des Sciences et Techniques , 6 avenue Victor le Gorgeu, C.S. 93837, 29238 Brest, Cedex 3, France.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Tripier
authors.affiliation: Centre de Biophysique Moléculaire, CNRS , rue Charles Sadron, 45071 Orléans, Cedex 2, France.|Le Studium, Loire Valley Institute for Advanced Studies , 1 Rue Dupanloup, 45000 Orléans, France.
authors.forename: Gyula
authors.initials: G
authors.lastname: Tircsó
authors.forename: Ferenc Krisztián
authors.initials: FK
authors.lastname: Kálmán
authors.forename: Attila Csaba
authors.initials: AC
authors.lastname: Bényei
authors.forename: Imre
authors.initials: I
authors.lastname: Tóth
authors.affiliation: Grupo QUICOOR, Centro de Investigaciones Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Universidade da Coruña , Campus da Zapateira, Rúa da Fraga 10, 15008 A Coruña, Spain.
authors.forename: Andrés
authors.initials: A
authors.lastname: de Blas
authors.affiliation: Grupo QUICOOR, Centro de Investigaciones Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Universidade da Coruña , Campus da Zapateira, Rúa da Fraga 10, 15008 A Coruña, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Rodríguez-Blas
authors.affiliation: Grupo QUICOOR, Centro de Investigaciones Científicas Avanzadas (CICA) and Departamento de Química Fundamental, Universidade da Coruña , Campus da Zapateira, Rúa da Fraga 10, 15008 A Coruña, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Platas-Iglesias