Syntheses, structures and magnetic properties of a series of lanthanide complexes with reduced nitronyl nitroxide radical ligands

A series of new lanthanide complexes [Ln(hfac)(3)](HIM-6-X-Py) 2-[HIM-6-X-Py = 2-(6-X-2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide; hfac = hexafluoroacetylacetonate; X = Br, Ln = Tb (Br-Tb), Dy (Br-Dy), Ho (Br-Ho), Er (Br-Er), Yb (Br-Yb); X = Cl, Ln = Dy (Cl-Dy); X = F, Ln = Dy (F-Dy)] have been prepared and studied. During the preparation of the lanthanide complexes, the nitronyl nitroxide radical ligands NIT-6-X-Py (2-(6-X-2-pyridyl)-4,4,5,5-tetramethylimidazolyl-1-oxyl-3-oxide; X = F, Cl, Br) were reduced to the non-radical ligands HIM-6-X-Py, forming mononuclear lanthanide complexes with two HIM-6-X-Py ligands chelated to one lanthanide(III) ion. The reduced ligands were evidenced by the color of the lanthanide complexes, the characteristic IR band of N-H stretching absorption, the residue electron density near the N atom of the ligand, and the N-O bond lengths in the final metal complexes. Except for compound F-Dy which crystallized in the triclinic space group P (1) over bar with two isolated Dy-III centers in an asymmetric unit, all other complexes crystallized in the monoclinic space group P2(1)/n. Due to the reduced non-radical ligands, the magnetic properties of all these complexes are consistent with mononuclear Ln(III) compounds. Alternating-current (ac) magnetic susceptibility investigations revealed that complexes Br-Dy, Br-Er, Br-Yb, Cl-Dy and F-Dy exhibit field-induced frequency dependence which indicates the slow magnetic relaxation of these complexes.

Automated summary

A series of new lanthanide complexes have been synthesized and studied, where the nitronyl nitroxide radical ligands were reduced to form non-radical ligands chelated to lanthanide(III) ions. The magnetic properties of these complexes are consistent with mononuclear Ln(III) compounds, and field-induced frequency dependence was observed in some complexes indicating slow magnetic relaxation.