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Incorporation of Trinuclear Lanthanide(III) Hydroxo Bridged Clusters in Macrocyclic Frameworks
A cluster of lanthanide(III) or yttrium(III)
ions, Ln<sub>3</sub>(μ<sub>3</sub>-OH)<sub>2</sub>, (Ln(III)
= Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Yb(III), or
Y(III)) can be bound in the center of a chiral macrocyclic amines
H<sub>3</sub>L1<sup><i>R</i></sup>, H<sub>3</sub>L1<sup><i>S</i></sup>, and H<sub>3</sub>L2<sup><i>S</i></sup> obtained in a reduction of a 3 + 3 condensation product of
(1<i>R</i>,2<i>R</i>)- or (1<i>S</i>,2<i>S</i>)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol
or 2,6-diformyl-4-<i>tert</i>butylphenol. X-ray crystal
structures of the Nd(III), Sm(III), Gd(III), Dy(III), and Y(III) complexes
reveal trinuclear complexes with Ln(III) ions bridged by the phenolate
oxygen atoms of the macrocycle as well as by μ<sub>3</sub>-hydroxo
bridges. In the case of the Nd(III) ion, another complex form can
be obtained, whose X-ray crystal structure reveals two trinuclear
macrocyclic units additionally bridged by hydroxide anions, corresponding
to a [Ln<sub>3</sub>(μ<sub>3</sub>-OH)]<sub>2</sub>(μ<sub>2</sub>-OH)<sub>2</sub> cluster encapsulated by two macrocycles.
The formation of trinuclear complexes is confirmed additionally by <sup>1</sup>H NMR, electrospray ionization mass spectrometry (ESI MS),
and elemental analyses. Titrations of free macrocycles with Sm(III)
or Y(III) salts and KOH also indicate that a trinuclear complex is
formed in solution. On the other hand, analogous titrations with La(III)
salt indicate that this kind of complex is not formed even with the
excess of La(III) salt. The magnetic data for the trinuclear Gd(III)
indicate weak antiferromagnetic coupling (<i>J</i> = −0.17
cm<sup>–1</sup>) between the Gd(III) ions. For the trinuclear
Dy(III) and Tb(III) complexes the χ<sub><i>M</i></sub><i>T</i> vs <i>T</i> plots indicate a more complicated
dependence, resulting from the combination of thermal depopulation
of <i>m</i><sub><i>J</i></sub> sublevels, magnetic
anisotropy, and possibly weak antiferromagnetic and ferromagnetic
interactions