New polyoxometalate-based mononuclear lanthanide complexes with slow relaxation of magnetization

A series of new polyoxometalate(POM)-based mononuclear lanthanide(III)–bi pyridine-N-oxide complexes, [Ln(bpyno)4][PMo12O40]·2H2O (Ln = Dy (1), Tb (2), Er (3), Ho (4); bpyno = 4,4′-dimethyl-2,2′-bipyridyl-N-N′-dioxide), have been synthesized by the reactions between LnPMo12O40 salts (Ln = Dy (1), Tb (2), Er (3), Ho (4)) and bpyno ligand. All compounds were characterized by elemental analyses, TG analyses, IR, powder X-ray diffraction and single-crystal X-ray diffraction. In 1–4, each mononuclear Ln center is coordinated by eight O atoms derived from four bpyno ligands, exhibiting an approximate square antiprismatic coordination geometry. Furthermore, the [Ln(bpyno)4]3+ units are well separated by the α-Keggin-type polyoxoanions. Magnetic measurements indicate that compound 1 exhibits frequency dependent ac magnetic susceptibilities indicative of slow relaxation of the magnetization.

Graphical abstractThe first polyoxometalate-based mononuclear lanthanide(III)-bipyridine-N-oxide complexes were prepared and the dysprosium(III)-containing system exhibits slow relaxation of magnetization.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The first polyoxometalate-based mononuclear Ln-bipyridine-N-oxide complexes were synthesized. ► [Ln(bpyNO)4]3+ units are well separated by the nanosized diamagnetic polyoxoanions. ► ac susceptibility measurements shows the slow relaxation of magnetization for the Dy-containing species. ► Compounds 1–4 may suggest a new synthetic model to modulate and construct new single-ion magnets.