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Structure and optical spectroscopy of holmium(III) triethylenetetraaminehexaacetate in single crystal and in solution.
Autorzy
Rok wydania
2000
Czasopismo
Numer woluminu
24
Strony
603-607
DOI
10.1039/B001480J
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
The crystal structure of [C(NH2)3]3[Ho(ttha)]·3H2O (H6ttha=triethylenetetraaminehexaacetic acid) has been determined. The coordination environment of the HoIII ion is composed of five carboxylate oxygen atoms and four nitrogen atoms. Electronic absorption spectra of a [C(NH2)3]3[Ho(ttha)]·3H2O single crystal were measured at room and liquid helium temperatures and compared with those of the HoIII–ttha (1:1) complex in solution. The results suggest that a species of coordination geometry similar to that of the [Ho(N4O5)]3− type found in the crystal exists predominantly in solution at pH>5. At lower pH values, as for other LnIII–ttha complexes, coordination equilibria are observed.This paper is a part of our investigation of lanthanide compounds with triethylenetetraaminehexaacetic acid (H6ttha), a ligand with four nitrogen and six oxygen donor atoms (N4O6). Our previous results based on the electronic absorption spectra of NdIII–ttha crystals and solutions of the complex revealed the existence of two different species at equilibrium in solution.1,2 In those species, the inner sphere of the NdIII ion comprises only donor atoms of the ttha ligand, forming [Nd(N4O6)]3− and [Nd2(N3O6)2]6−/[Nd(N3O6)]3− entities with coordination numbers of ten and nine, respectively. In order to check how coordination arrangements around the LnIII ion will change across the rare earth series in the ttha complexes, we have performed spectroscopic investigations of the HoIII–ttha complex in solution and in the form of a single crystal. Such studies seem to be essential since previously obtained results on complexes of heavy lanthanide ions with ttha in solution proved the absence of water molecules in the inner sphere of the LnIII ion,3–5 formation of oligomeric species6 as well as a presence of multiple 1:1 species.3,7 So far two types of crystal structure of nine-coordinate ttha complexes with heavy lanthanide ions have been determined, namely: [Ln(N4O5)]3− (where LnIII=Gd,8 Dy,9 Yb10) and [Gd2(N3O6)2]6−,11 the latter being similar to that found for the NdIII–ttha complex.2 The aim of this paper is to recognize the solution structure of the HoIII–ttha (1:1) complex based on a comparison between the spectral properties of this complex in the [C(NH2)3]3[Ho(ttha)]·3H2O single crystal and in solution.
Adres publiczny
DOI https://doi.org/10.1039/B001480J
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