H. Naruke et T. Yamase, STRUCTURE OF DIALUMINIOHEXALUTETIOPENTAKIS(HEXANIOBATE) - COMPARISON WITH EUROPIUM AND ERBIUM ANALOGS, Journal of alloys and compounds, 255(1-2), 1997, pp. 183-189
The structure of a6.5H19.5[{Lu3O(OH)(3)(H2O)(3)}(2)Al-2(Nb6O19)(5)] .
38H(2)O was determined by X-ray diffraction analysis and compared with
isomorphous Eu- and Er-complexes to investigate the effect of the ion
ic radii of the lanthanide cations (Eu3+:1.066; Er3+:1.004; Lu3+:0.977
Angstrom, for eight-fold coordination) on the molecular structure. A
central [{Lu3O(OH)(3)(H2O)(3)}(2)](8+) core in the [{Lu3O(OH)(3)(H2O)(
3)}(2)Al-2(Nb6O19)(5)](26-) anion was attached by both three equatoria
l [Nb6O19](8-) and two axial [A1(Nb6O19)](5-) groups with approximatel
y D-3 point symmetry. The three Lu atoms in a [Lu3O(OH)(3)(H2O)(3)](4) group, a half [{Lu3O(OH)(3)(H2O)(3)}(2)](8+) core, achieved eight-fo
ld coordination with O atoms; one mu(3)-O, two OH-, one terminal H2O a
nd four O atoms belonging to the equatorial [Nb6O19](8-) groups. The m
ean Lu...Lu distance within each of the two Lu-3 traids is 3.676(6) An
gstrom, while that between the two different Lu-3 traids is 4.69(5) An
gstrom. The former distance is short compared with that of Eu-complex
(3.76(2) Angstrom) but somewhat long compared with that of the Er-comp
lex (3.66(1) Angstrom). The latter distance is comparable to the corre
sponding distance (4.69(6) Angstrom) of the Eu-complex, and slightly l
ong compared with that of the Er-complex (4.62(4) Angstrom). The small
size of the Lu3+ cation was reflected by a contraction of the [{Lu3O(
OH)(3)(H2O)(3)}(2)](8+) core. This effect represents a shift in the th
ree equatorial [Nb6O19](8-) groups toward the center of the complex by
about 0.13 and 0.05 Angstrom, compared with Eu- and Er-complexes, res
pectively.