Incorporation of Trinuclear Lanthanide(III) Hydroxo Bridged Clusters in Macrocyclic Frameworks

Abstract

A cluster of lanthanide­(III) or yttrium­(III) ions, Ln₃(μ₃-OH)₂, (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 H₃L1^<i>R</i>, H₃L1^<i>S</i>, and H₃L2^<i>S</i> 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 μ₃-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 [Ln₃(μ₃-OH)]₂(μ₂-OH)₂ cluster encapsulated by two macrocycles. The formation of trinuclear complexes is confirmed additionally by ¹H 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^–1) between the Gd­(III) ions. For the trinuclear Dy­(III) and Tb­(III) complexes the χ_<i>M</i><i>T</i> vs <i>T</i> plots indicate a more complicated dependence, resulting from the combination of thermal depopulation of <i>m</i>_<i>J</i> sublevels, magnetic anisotropy, and possibly weak antiferromagnetic and ferromagnetic interactions