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Inne
Unusual coordination behaviour of a phosphonate- and pyridine-containing ligand in a stable lanthanide complex.
Autorzy
Rok wydania
2010
Czasopismo
European Journal of Inorganic Chemistry
Strony
1696-1702
DOI
10.1002/ejic.201000058
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
An experimental study of the coordination of lanthanide ions with {ethane‐1,2‐diylbis[imino(pyridin‐2‐ylmethanediyl)]}bis(phosphonic acid), a ligand containing phosphonate and pyridine arms attached to the well‐known ethylenediamine scaffold, is reported. The X‐ray crystal structure of an anionic, octacoordinate EuIII complex of the formula [C(NH2)]6[Eu2(L)2(CO3)2]·8H2O has been obtained and found to contain cyclic dimeric complex anions in which the coordination environment of each EuIII ion is composed of three oxygen atoms from phosphonate groups, two nitrogen atoms from imino groups and one nitrogen atom from a pyridine group, a combination that has seldom been observed for LnIII complexes. In order to check the coordination behaviour of the ligand, an investigation of the complexes in solution has been performed, which revealed a different coordination mode. The protonation constants of the free ligand and the stability constants of their complexes with selected lanthanide ions (LaIII, SmIII, EuIII, GdIII, TbIII, HoIII and LuIII) have been determined potentiometricaly at 25 °C and an ionic strength of 0.1 M (KCl). The results obtained show the formation of monomeric, protonated ([LnH2L], [LnHL]) and nonprotonated ([LnL]) species in the pH range studied (2–11). The determined stability constants (log βLnL) are relatively high, varying between 14.96 and 16.42. The EuIIIL system was also fully characterized by means of UV/Vis spectroscopy, which indicated that the coordination process starts above pH 3 and remains constant in the range pH 4–10. In contrast to the crystal structure, solution NMR and luminescence studies suggested that the pyridine moieties are not present in the LnIII coordination sphere. These results suggest that this ligand–unsaturated metal ion coordination sphere may provide a potential binding site for other target molecules.
Słowa kluczowe
lanthanides, N, P ligands, Stability constants, Coordination modes
Adres publiczny
https://doi.org/10.1002/ejic.201000058
Strona internetowa wydawcy
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