Lanthanide Complexes Based on a Diazapyridinophane Platform Containing Picolinate Pendants

• Published in: Inorganic chemistry 2012-10, Vol.51 (20), p.10893-10903
• Main Authors: Roca-Sabio, Adrián, Bonnet, Célia S, Mato-Iglesias, Marta, Esteban-Gómez, David, Tóth, Éva, Blas, Andrés de, Rodríguez-Blas, Teresa, Platas-Iglesias, Carlos
• Format: Article
• Language: English
• Subjects: Biochemistry, Molecular Biology; Lanthanoid Series Elements; Lanthanoid Series Elements - chemistry; Life Sciences; Ligands; Models, Molecular; Molecular Conformation; Organometallic Compounds; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Picolinic Acids; Picolinic Acids - chemistry; Protons; Pyridines; Pyridines - chemistry; Quantum Theory
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic301369z

A new macrocyclic ligand, N,N′-bis[(6-carboxy-2-pyridyl)methyl]-2,11-diaza[3.3](2,6)pyridinophane (H2BPDPA), was prepared, and its coordination properties toward the LnIII ions were investigated. The hydration numbers (q) obtained from luminescence lifetime measurements in aqueous solution of the EuIII and TbIII complexes indicate that they contain one inner-sphere water molecule. The structure of the complexes in solution has been investigated by 1H and 13C NMR spectroscopy, as well as by theoretical calculations performed at the density functional theory (B3LYP) level. The minimum-energy conformation calculated for the YbIII complex is in excellent agreement with the experimental structure in solution, as demonstrated by analysis of the YbIII-induced paramagnetic 1H shifts. Nuclear magnetic relaxation dispersion (NMRD) profiles and 17O NMR measurements recorded on solutions of the GdIII 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 × 106 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.