Lanthanide Complexes of Tritopic Bis(hydrazone) Ligands: Single-Molecule Magnet Behavior in a Linear Dy3III Complex

Tritopic pyridinebis(hydrazone)-based ligands typically produce square M-9 [3 X 3] grid complexes with first-row transition-metal ions (e.g., M = Mn, Fe, Co, Cu, Zn), but with larger lanthanide ions, such coordination motifs are not produced, and instead linear trinuclear complexes appear to be a preferred option. The reaction of 2pomp [derived from pyridine-2,6-bis(hydrazone) and 2-acetylpyridine] with La-III, and Dy-III salts produces helical linear trinuclear [Ln(3)(2pomp)(2)]-based complexes, where each metal ion occupies one of the three tridentate ligand pockets. Two ligands encompass the three metal ions, and internal connections between metal ions occur through mu-O-hydrazone bridges. Coligands include benzoate, nitrate, and N,N-dimethylformamide. The linear Dy-3(III) complex exhibits single-molecule magnet behavior, demonstrated through alternating-current susceptibility measurements. Slow thermal magnetic relaxation was detected in an external field of 1800 Oe, where quantum-tunneling effects were suppressed (U-eff = 14 K).