Tetranuclear and Pentanuclear Compounds of the Rare-Earth Metals: Synthesis and Magnetism

The Schiff-base proligand 4-tert-butyl-2,6-bis-[(2-hydroxy-phenylimino)­methyl]­phenol
(H3L) was prepared in situ from 4-tert-butyl-2,6-diformylphenol and 2-aminophenol. The proligand (H3L) was used with dibenzoylmethane (DBMH) or acetylacetone
(acacH) with lanthanides giving compounds with varying arrangements
of metal atoms and nuclearities. The tetranuclear compound {[Dy4(L)3(DBM)4]­[Et3NH]} (1) and pentanuclear compound {[Dy5(μ3-OH)2(L)3(DBM)4(MeOH)4]·4­(MeOH)} (2) were obtained from the ligand
(L)3– and dibenzoylmethane. The tetranuclear compounds
{[Dy4(μ4-OH)­(L)2(acac)4(MeOH)2(EtOH)­(H2O)]·(NO3)·2­(MeOH)·3­(EtOH)} (3) and {[Ln4(μ3-OH)2(L)­(HL)­(acac)5(H2O)] (HNEt3)­(NO3)·2­(Et2O)} (Ln = Tb (4), Dy (5), Ho (6), and Tm (7)) resulted when the ligand (L)3– was used in the presence of acetylacetone. In the solid state structures,
the tetranuclear compound 1 adopts a linear arrangement
of metal atoms, while tetranuclear compound 3 has a square
grid arrangement of metal atoms, and tetranuclear compounds 4–7 have a seesaw-shaped arrangement of
metal atoms. The composition found from single-crystal X-ray analysis
of compound 1 and 3–7 is supported by electrospray ionization mass spectrometry (ESI-MS).
The magnetic studies on compounds 1 suggest the presence
of weak ferromagnetic interactions, whereas compounds 2–6 exhibit weak antiferromagnetic interactions
between neighboring metal centers. Compounds 1, 2, and 3 also show single-molecule magnet behavior
under an applied dc field.