First examples of rare earth benzoate chain complexes doped with radicals as paramagnetic carriers: Synthesis, structure, and magnetic properties

Four new lanthanide complexes {[Ln(pnba)3(H2O)2]·(NITpPy)·(MeOH)}n (Ln = Gd (1), Tb (2), Yb (3), and {[Yb(pnba)3(H2O)]·(NITmPy)}n (4) (Hpnba = p-nitrobenzoic acid; NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide; NITmPy = 2-(3-pyridyl)-4,4,5,5-tetra-methyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide) were synthesized and characterized. Single crystal X-ray analyses reveal that complexes 1, 2, and 3 are isomorphous, and the center LnIII ions are eight-coordinated. Alternate (μ2-η2:η1)2 and (μ2-η1:η1)2 type bridging modes by carboxylate ligands result in the formation of chain skeletons with two different Ln⋯Ln distances. However, in complex 4, Yb ions are seven-coordinated and bridged by a sole (μ2-η1:η1)3 mode pnba. In the four complexes, radicals that are paramagnetic spin carriers are doped in as guest molecules and are located between the columns composed of LnIII ions through weak intermolecular interactions. In addition, short contact between ORadical atoms with LnIII ions was observed. Careful inspection of the structures reveals that guest molecules have a significant function in determining the structure. Magnetic measurements were performed for complexes 1, 2, and 4. The magnetic studies show that very weak antiferromagnetic couplings exist between GdIII–GdIII in complex 1.