Dinuclear Fluoride Single-Bridged Lanthanoid Complexes as Molecule Magnets: Unprecedented Coupling Constant in a Fluoride-Bridged Gadolinium Compound

Capturing Metal Fluoride inside a Carbon Cage

We report here a new type of metal fluoride cluster that can be stabilized inside fullerene via in situ fluorine encapsulation followed by exohedral trifluoromethylation, giving rise to rare-earth metal fluoride clusterfullerenes (FCFs) M2F@C80(CF3) (M = Gd and Y). The molecular structure of Gd2F@C80(CF3) was unambiguously determined by single-crystal X-ray analysis to show a μ2-fluoride-bridged Gd-F-Gd cluster with short Gd-F bonds of 2.132(7) and 2.179(7) Å. The 19F NMR spectrum of the diamagnetic Y2F@C80(CF3) confirms the existence of the endohedral F atom, which exhibits a triplet with a large 19F-89Y coupling constant of 74 Hz and a high temperature sensitivity of the 19F chemical shift of 0.057 ppm/K. Theoretical studies reveal the ionic Y-F bonding nature arising from the highest electronegativity of the F element and an electronic configuration of [Y2F]5+@[C80]5- with an open-shell carbon cage, which thus necessitates the stabilization of FCFs by exohedral trifluoromethylation.

Lanthanide Metal-Organic Frameworks Exhibiting Fluoro-Bridged Extended Chains: Synthesis, Crystal Structures, and Magnetic Properties

Two fluoro-bridged lanthanide-containing metal-organic frameworks (MOFs) were synthesized using 2,2'-bipyridine-4,4'-dicarboxylic acid (BPDC), a fluorinated modulator, and a lanthanide nitrate. The syntheses of MOFs containing Gd3+ or Tb3+ and a closely related MOF structure containing Ho3+, Gd3+, or Tb3+ are presented. The presence of the fluorinated metal chains in these MOFs is shown through single crystal X-ray diffraction, energy dispersion X-ray spectroscopy, 19F nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Magnetic measurements reveal weak antiferromagnetic exchange between the Ln3+ ions mediated by fluoride anions along the zigzag ladder chains present in the crystal structures of these MOFs.

Dy4, Dy5, and Ho2 Complexes of an N3O2 Aminophenol Donor: A Dy5-µ3-Peroxide Single Molecule Magnet

The reactivity of the new flexible potentially pentadentate N₃O₂ aminophenol ligand H₄L^r (2,2'-((pyridine-2,6-diylbis(methylene))bis(azanediyl))diphenol) towards different dysprosium salts and holmium(III) nitrate was investigated. Accordingly, this reactivity seems to greatly depend on the metal ion and salt employed. In this way, the reaction of H₄L^r with dysprosium(III) chloride in air leads to the oxo-bridged tetranuclear complex [Dy₄(H₂L^r)₃(Cl)₄(μ₃-O)(EtOH)₂(H₂O)₂]·2EtOH·H₂O (1·2EtOH·H₂O), while the same reaction just changing the chloride salt by the nitrate one renders the peroxo-bridged pentanuclear compound [Dy₅(H₂L^r)₂(H_2.5L^r)₂(NO₃)₄(µ₃-O₂)₂]·2H₂O (2·2H₂O), where both peroxo ligands seem to come from the fixation and reduction of atmospheric oxygen. However, if holmium(III) nitrate is used instead of dysprosium(III) nitrate, no evidence of a peroxide ligand is observed, and the dinuclear complex {[Ho₂(H₂L^r)(H₃L^r)(NO₃)₂(H₂O)₂](NO₃)} 2.5H₂O (3·2.5H₂O) is isolated. The three complexes were unequivocally characterized by X-ray diffraction techniques, and their magnetic properties were analyzed. Thus, while the Dy₄ and Ho₂ complexes do not show magnet-like behavior even in the presence of an external magnetic field, 2·2H₂O is a single molecule magnet, with an U_eff barrier of 61.2 K (43.2 cm^-1). This is the first homonuclear lanthanoid peroxide SMM, which also shows the highest barrier among the reported 4f/3d peroxide zero field SMMs to date.

Fluoride-bridged dinuclear dysprosium complex showing single-molecule magnetic behavior: supramolecular approach to isolate magnetic molecules

Using Na-encapsulated benzo[18]crown-6 (Na)(B18C6) as a counter cation, we successfully magnetically isolated a fluoride-bridging Dy dinuclear complex {[(PW₁₁O₃₉)Dy(H₂O)₂]₂F} (Dy₂POM) with lacunary Keggin ligands. (Na)(B18C6) formed two types of tetramers through C-H⋯O, π⋯π and C-H⋯π interactions, and each tetramer aligned in one dimension along the c-axis to form two types of channels. One channel was partially penetrated by a supramolecular cation from the ±a-axis direction, dividing the channel in the form of a "bamboo node". Dy₂POM was spatially divided by this "bamboo node," which magnetically isolated one portion from the other. The temperature dependence of the magnetic susceptibility indicated a weak ferromagnetic interaction between the Dy ions bridged by fluoride. Dy₂POM exhibited the magnetic relaxation characteristics of a single-molecule magnet, including the dependence of AC magnetic susceptibility on temperature and frequency. Magnetic relaxation can be described by the combination of thermally active Orbach and temperature-independent quantum tunneling processes. The application of a static magnetic field effectively suppressed the relaxation due to quantum tunneling.