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

Abstract A series of lanthanide(III) oxamate complexes of formula Na[Eu(4-HOpa) 4 (H 2 O)]∙2H 2 O ( 1 ), Na[Gd(4-HOpa) 4 (H 2 O)]∙2H 2 O ( 2 ), Na[Dy(4-HOpa) 4 (H 2 O)]∙2H 2 O ( 3 ), and Na[Ho(4-HOpa) 4 (H 2 O)]∙2H 2 O ( 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 P 2 1 / n space group of the monoclinic system. The crystal structures of 1 – 4 consist of mononuclear lanthanide(III) complex anions, [Ln(4-HOpa) 4 (H 2 O)] − (Ln = Eu 3+ , Gd 3+ , Dy 3+ , and Ho 3+ ), coordinated sodium(I) countercations, and crystallization water molecules, resulting in a 2D Na I Ln III supramolecular coordination network. The coordination sphere of Ln 3+ 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 Gd 3+ ions under DC applied field of 1.0 kOe, behaving as a field-induced single-ion magnet as occurs for the Dy 3+ complex 3 . The Eu 3+ complex 1 has a nonmagnetic ground state, while the Ho 3+ compound 4 behave as a paramagnet, and do not exhibit relaxation of the magnetization with or without an applied field.