Abstract
A family of four Ln(III) complexes has been synthesized with the general formula [Ln2(NO3)4(L)2(S)] (Ln = Gd, Tb, Er, and S = H2O; 1, 2 and 4, respectively/Ln = Dy, S = MeOH, complex 3), where HL is the flexible ditopic ligand N’-(1-(pyridin-2-yl)ethylidene)pyridine-2-carbohydrazide. The structures of isostructural MeOH/H2O solvates of these complexes were determined by single-crystal X-ray diffraction. The two LnIII ions are doubly bridged by the deprotonated oxygen atoms of two “head-to-head” 2.21011 (Harris notation) L¯ ligands, forming a central, nearly rhombic {LnIII2(μ-OR)2}4+ core. Two bidentate chelating nitrato groups complete a sphenocoronal 10-coordination at one metal ion, while two bidentate chelating nitrato groups and one solvent molecule (H2O or MeOH) complete a spherical capped square antiprismatic 9-coordination at the other. The structures are critically compared with those of other, previously reported metal complexes of HL or L¯. The IR spectra of 1–4 are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The f-f transitions in the solid-state (diffuse reflectance) spectra of the Tb(III), Dy(III), and Er(III) complexes have been fully assigned in the UV/Vis and near-IR regions. Magnetic susceptibility studies in the 1.85–300 K range reveal the presence of weak, intramolecular GdIII∙∙∙GdIII antiferromagnetic exchange interactions in 1 [J/kB = −0.020(6) K based on the spin Hamiltonian Ĥ = −2J(ŜGd1∙ ŜGd2)] and probably weak antiferromagnetic LnIII∙∙∙LnIII exchange interactions in 2–4. Ac susceptibility measurements in zero dc field do not show frequency dependent out-of-phase signals, and this experimental fact is discussed for 3 in terms of the magnetic anisotropy axis for each DyIII center and the oblate electron density of this metal ion. Complexes 3 and 4 are Single-Molecule Magnets (SMMs) and this behavior is optimally observed under external dc fields of 600 and 1000 Oe, respectively. The magnetization relaxation pathways are discussed and a satisfactory fit of the temperature and field dependencies of the relaxation time τ was achieved considering a model that employs Raman, direct, and Orbach relaxation mechanisms.
Highlights
Devices in the future, such as hard disks, will use components made from molecules instead of the traditional silicon-based electronics [1]
Taking into account the above information, we report in this paper on the reactions between hydrated gadolinium(III), terbium(III), dysprosium(III) and erbium(III) nitrates and LH, which have led to the desired asymmetric dinuclear complexes
Spectroscopic Characterization led to the desired asymmetric dinuclear complexes
Summary
Devices in the future, such as hard disks, will use components made from molecules instead of the traditional silicon-based electronics [1]. The great success of Ln(III)s to design SMMs is due to their contracted valence 4f orbitals, a feature that affects both structural and magnetic characteristics [36,37,38] These orbitals engage in weak, mainly electrostatic interactions with ligands’ orbitals and are nearly degenerate in energy, leading to impressive single-ion magnetic anisotropies in Ln(III) complexes. If: (i)coordination the ligand contains one monoanionic bridging atom or group between asymmetrically metal ion’s own. (ii) it is not very bulky, favoring the incorporation of two or group between asymmetrically disposed terminal coordination sites; (ii) it is not very bulky, III center ligands per dinuclear moiety;. III ions (“hard” acids) leaving the closest nitrogen atom of would be the bridging towardswould the Lnbe according to the HSABone principle) the bridging one towards the LnIII ions (“hard” acids) the central free, i.e., non-coordinated; turned out to be the casethis,.
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