title: Lanthanide complexes based on a diazapyridinophane platform containing picolinate pendants.
abstract: A new macrocyclic ligand, N,N'-bis[(6-carboxy-2-pyridyl)methyl]-2,11-diaza[3.3](2,6)pyridinophane (H(2)BPDPA), was prepared, and its coordination properties toward the Ln(III) ions were investigated. The hydration numbers (q) obtained from luminescence lifetime measurements in aqueous solution of the Eu(III) and Tb(III) complexes indicate that they contain one inner-sphere water molecule. The structure of the complexes in solution has been investigated by (1)H and (13)C NMR spectroscopy, as well as by theoretical calculations performed at the density functional theory (B3LYP) level. The minimum-energy conformation calculated for the Yb(III) complex is in excellent agreement with the experimental structure in solution, as demonstrated by analysis of the Yb(III)-induced paramagnetic (1)H shifts. Nuclear magnetic relaxation dispersion (NMRD) profiles and (17)O NMR measurements recorded on solutions of the Gd(III) complex were used to determine the parameters governing the relaxivity. The results show that this system is endowed with a relatively fast water-exchange rate k(ex)(298) = 63 × 10(6) s(-1). Thermodynamic stability constants were determined by pH-potentiometric titration at 25 °C in 0.1 M KCl. The stability constants, which fall within the range logK(LnL) = 12.5-14.2, point to a relatively low stability of the complexes primarily as a consequence of the low basicity of the ligand.
authors.affiliation: Departamento de Química Fundamental, Facultade de Ciencias, Universidade da Coruña, Campus da Zapateira, Rúa da Fraga 10, 15008 A Coruña, Spain.
authors.forename: Adrián
authors.initials: A
authors.lastname: Roca-Sabio
authors.forename: Célia S
authors.initials: CS
authors.lastname: Bonnet
authors.forename: Marta
authors.initials: M
authors.lastname: Mato-Iglesias
authors.forename: David
authors.initials: D
authors.lastname: Esteban-Gómez
authors.forename: Éva
authors.initials: É
authors.lastname: Tóth
authors.forename: Andrés
authors.initials: A
authors.lastname: de Blas
authors.forename: Teresa
authors.initials: T
authors.lastname: Rodríguez-Blas
authors.forename: Carlos
authors.initials: C
authors.lastname: Platas-Iglesias
mesh_terms: D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010848:Picolinic Acids / Q000737:chemistry*; D011522:Protons; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D028581:Lanthanoid Series Elements; D008024:Ligands; D009942:Organometallic Compounds; D010848:Picolinic Acids; D011522:Protons; D011725:Pyridines; C030614:picolinic acid