A. Mondry et P. Starynowicz, Structure and optical spectroscopy of holmium(III) triethylenetetraaminehexaacetate in single crystal and in solution, NEW J CHEM, 24(8), 2000, pp. 603-607
The crystal structure of [C(NH2)(3)](3)[Ho(ttha)] . 3H(2)O (H(6)ttha = trie
thylenetetraaminehexaacetic acid) has been determined. The coordination env
ironment of the Ho-III ion is composed of five carboxylate oxygen atoms and
four nitrogen atoms. Electronic absorption spectra of a [C(NH2)(3)](3)[Ho(
ttha)] . 3H(2)O single crystal were measured at room and liquid helium temp
eratures and compared with those of the Ho-III-ttha (1:1) complex in soluti
on. The results suggest that a species of coordination geometry similar to
that of the [Ho(N4O5)](3-) type found in the crystal exists predominantly i
n solution at pH > 5. At lower pH values, as for other Ln(III)-ttha complex
es, coordination equilibria are observed.