Slow magnetic relaxation in mononuclear gadolinium(III) and dysprosium(III) oxamato complexes

• Published in: Polyhedron 2019-09, Vol.169, p.102-113
• Main Authors: da Cunha, Tamyris T., Barbosa, Vitor M.M., Oliveira, Willian X.C., Pinheiro, Carlos B., Pedroso, Emerson F., Nunes, Wallace C., Pereira, Cynthia L.M.
• Format: Article
• Language: English
• Subjects: Crystal structures; Lanthanide complexes; Oxamate ligands; Single-ion magnets; Slow magnetic relaxation
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2019.04.056

Synthesis, crystal structures and magnetic properties of four mononuclear complexes containing Eu3+, Dy3+, Gd3+, and Ho3+ with the new hydroxyphenyloxamate ligand were studied. Slow relaxation of magnetization phenomena were observed for Dy3+ and Gd3+ compounds, which can be considered Single-Ion Magnets. [Display omitted] A series of lanthanide(III) oxamate complexes of formula Na[Eu(4-HOpa)4(H2O)]∙2H2O (1), Na[Gd(4-HOpa)4(H2O)]∙2H2O (2), Na[Dy(4-HOpa)4(H2O)]∙2H2O (3), and Na[Ho(4-HOpa)4(H2O)]∙2H2O (4) (4-HOpa = N-4-hydroxyphenyloxamate) were synthesized and characterized. The crystal structures of complexes 1–4, as well as the oxamate ligand in the ethyl ester acid form (Et[4-HOpa]), were elucidated by single crystal X-ray diffraction. 1–4 are isostructural, and they crystallize in the P21/n space group of the monoclinic system. The crystal structures of 1–4 consist of mononuclear lanthanide(III) complex anions, [Ln(4-HOpa)4(H2O)]− (Ln = Eu3+, Gd3+, Dy3+, and Ho3+), coordinated sodium(I) countercations, and crystallization water molecules, resulting in a 2D NaILnIII supramolecular coordination network. The coordination sphere of Ln3+ ions consists of square-face capped square antiprism (SAPRS-9). Magnetic properties were investigated for 1–4 in the 2–300 K temperature range using polycrystalline samples. Complex 2 exhibits an unusual and rare slow-relaxation of the magnetization for Gd3+ ions under DC applied field of 1.0 kOe, behaving as a field-induced single-ion magnet as occurs for the Dy3+ complex 3. The Eu3+ complex 1 has a nonmagnetic ground state, while the Ho3+ compound 4 behave as a paramagnet, and do not exhibit relaxation of the magnetization with or without an applied field.