Dramatic increase of selectivity for heavy lanthanide(III) cations by tuning the flexibility of polydentate chelators

Lorenzo Tei, Z. Baranyai, E. Brücher, Claudio Cassino, Fabio Demicheli, Norberto Masciocchi, Giovanni B. Giovenzana, Mauro Botta

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Two novel octadentate ligands have been synthesized by attaching two terminal iminodiacetic groups to either 1,4-diazepane (BCAED) or piperazine (BCAEP) as central scaffold. The introduction of the seven- or six-membered ring into the ligand backbone is expected to modify their overall flexibility and then to affect the stability of the corresponding lanthanide(II) complexes. In this work, thermodynamic stability data are determined for the formation of the complexes of BCAED and BCAEP with La3+, Nd3+, Eu 3+, Gd3+, Ho3+, and Lu3+. The ligand BCAED shows a strong bindingj affinity for Lu3+ (log K=20.99), moderate for Gd3+ (logK=17.15) and rather weak for La3+ (logK=12.77). Thus, the variation of logK across the Ln series assumes the remarkable value of 8.22, the largest so far reported. This points to a predominant role of a suitable size match between the metal ion and the ligand cavity, determined by its structure and flexibility. The ligand BCAEP forms less stable complexes with lanthanide(III) cations although it retains a good selectivity (ΔlogKLa-Lu=5.66). The Gd(III) complexes have been investigated in aqueous solution by measuring their relaxivity as a function of pH, at 20 MHz and 25°C. The results can be interpreted very well in terms of the species distribution curves calculated from the thermodynamic data and indicate that in these complexes Gd3+ is octacoordinated, without any bound water molecule. This coordination geometry is maintained in the solid state as shown by the X-ray crystal structure of [Na(H2O) 2][Gd(BCAED)] where the metal ¡is at the center of a bicappedtrigonal prism. Finally, the 13C NMR spectra (9.4 T, 25°C) of the diamagnetic La3+, Y3+, and Lu 3+ complexes show that a pronounced stereochemical rigidity is associated with the thermodynamically more stable complexes.

Original languageEnglish
Pages (from-to)616-625
Number of pages10
JournalInorganic Chemistry
Volume49
Issue number2
DOIs
Publication statusPublished - Jan 18 2010

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Lanthanoid Series Elements
Chelating Agents
Cations
flexibility
Tuning
selectivity
tuning
Ligands
cations
ligands
thermodynamics
Prisms
rigidity
Scaffolds
Rigidity
prisms
Metal ions
affinity
metal ions
Thermodynamic stability

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Dramatic increase of selectivity for heavy lanthanide(III) cations by tuning the flexibility of polydentate chelators. / Tei, Lorenzo; Baranyai, Z.; Brücher, E.; Cassino, Claudio; Demicheli, Fabio; Masciocchi, Norberto; Giovenzana, Giovanni B.; Botta, Mauro.

In: Inorganic Chemistry, Vol. 49, No. 2, 18.01.2010, p. 616-625.

Research output: Contribution to journalArticle

Tei, Lorenzo ; Baranyai, Z. ; Brücher, E. ; Cassino, Claudio ; Demicheli, Fabio ; Masciocchi, Norberto ; Giovenzana, Giovanni B. ; Botta, Mauro. / Dramatic increase of selectivity for heavy lanthanide(III) cations by tuning the flexibility of polydentate chelators. In: Inorganic Chemistry. 2010 ; Vol. 49, No. 2. pp. 616-625.
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AU - Masciocchi, Norberto

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