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 P 2 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 ( P 2 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 =‐2 J GdRad ( S Gd1 S Rad1 + S Gd2 S Rad2 ], 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.