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

The Schiff-base proligand 4-tert-butyl-2,6-bis-[(2-hydroxyphenylimino)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 nudearities. The tetranudear compound {[Dy-4(L)(3)(DBM)(4)][Et3NH]} (1) and p entanudear compound {[Dys (mu(3)-OH)(2)(L)(3)(DBM)(4)(MeOH)(4)(MeOH)} (2) were obtained from the ligand (L)(3-) and dibenzoylmethane. The tetranuclear compounds {[Dy-4(t44-OH)(L)2(acac)4(Me0H)2(Et0H)(H20)](NO3)-2(Me0H).3(Et0H)} (3) and {[Ln(4)(3-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)' - was used in the presence of acetylacetone. In the solid state structures, the tetranuclear compound 1 adopts a linear arrangement of metal atoms, while tetranudear 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 Xray 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.