title: Definition of the Labile Capping Bond Effect in Lanthanide Complexes.
abstract: Two macrocyclic ligands containing a cyclen unit, a methyl group, a picolinate arm, and two acetate pendant arms attached to two nitrogen atoms of the macrocycle either in trans (1,7-H3Medo2 ampa = 2,2'-(7-((6-carboxypyridin-2-yl)methyl)-10-methyl-1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetic acid) or in cis (1,4-H3Medo2 ampa) positions are reported. These ligands provide eight-coordination to the Ln3+ions, leaving a coordination position available for a water molecule that occupies a capping position in the twisted square antiprismatic polyhedron (1,4-H3Medo2 ampa) or one of the positions of the square antiprism (1,7-H3Medo2 ampa). The charge neutral [Gd(1,7-Medo2 ampa)] complex presents an unprecedentedly low water-exchange rate (kex298=8.8×103s-1), whereas water exchange in [Gd(1,4-Medo2 ampa)] is three orders of magnitude faster (kex298=6.6×106s-1). These results showcase the labile capping bond phenomenon: A ligand occupying a capping position is hindered by the environment and thus is intrinsically labile.
authors.affiliation: Centro de Investigaciones Científicas Avanzadas (CICA), Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, 15071, A Coruña, Galicia, 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: Centro de Investigaciones Científicas Avanzadas (CICA), Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, 15071, A Coruña, Galicia, Spain.
authors.forename: Martín
authors.initials: M
authors.lastname: Regueiro-Figueroa
authors.affiliation: Centro de Investigaciones Científicas Avanzadas (CICA), Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, 15071, A Coruña, Galicia, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Esteban-Gómez
authors.affiliation: Centro de Investigaciones Científicas Avanzadas (CICA), Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, 15071, A Coruña, Galicia, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Rodríguez-Blas
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: Véronique
authors.initials: V
authors.lastname: Patinec
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: Department of Inorganic and Analytical Chemistry, University of Debrecen, 4010, Debrecen, Egyetem tér 1, Hungary.
authors.forename: Gyula
authors.initials: G
authors.lastname: Tircsó
authors.affiliation: Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121, Alessandria, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Carniato
authors.affiliation: Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Viale T. Michel 11, 15121, Alessandria, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Botta
authors.affiliation: Centro de Investigaciones Científicas Avanzadas (CICA), Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, 15071, A Coruña, Galicia, Spain.
authors.forename: Carlos
authors.identifier: http://orcid.org/0000-0002-6989-9654
authors.initials: C
authors.lastname: Platas-Iglesias
keywords: NMR spectroscopy; density functional calculations; gadolinium; magnetic resonance imaging; water exchange