Magnetic Molecular Rectangles Constructed from Functionalized Nitronyl-Nitroxide Ligands and Lanthanide(III) Ions

Five binuclear complexes with rectangular topology have been synthesized using a nitronyl-nitroxide ligand (L) functionalized with a pyrazole coordinating group: [Ln(2)(hfac)(2)L-2], with Ln=Eu (1), Gd (2 a, 2 b), Tb (3), Dy (4), Tm (5). The Eu-III and Tm-III complexes crystallize in the P2(1)/n space group, while the Gd-III, Tb-III, and Dy-III derivatives crystalize in P-1 space group. The crystal structures for compounds 2 a, 3, 4, and 5 have been fully solved, while for compounds 1 and 2 b, the unit cell parameters have been measured and compared with crystals 3 and 5. Crystals 2 a (P2(1)/n) and 2 b (P-1) are polymorphic forms. In these complexes the nitronyl-nitroxide ligand bridges two metal ions through one aminoxyl group and the pyrazole fragment. In the five complexes the Ln(III) ions show a coordination number of eight with a triangular dodecahedron geometry. The magnetic properties of all five complexes have been investigated. For compounds 2, 3, and 4 the Ln(III)-Rad interaction was found to be ferromagnetic: J(GdRad)=2.09(1) cm(-1) [H=-2J(GdRad)(SGd1SRad1+SGd2SRad2], J(TbRad)=1.93(14) cm(-1), J(DyRad)=1.72(14) cm(-1). The Tm-III-Rad coupling is antiferromagnetic (J(TmRad)=-0.53(1) cm(-1)). For the Tb-III, Dy-III, and Tm-III complexes the effects of the crystal field have been taken into account in the fitting procedure.

Automated summary

Five binuclear complexes with rectangular topology, including Eu, Gd, Tb, Dy, and Tm compounds, have been synthesized and their magnetic properties show significant differences.