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.

希夫碱前配体（Schiff-base proligand）4-叔丁基-2,6-双[(2-羟基苯亚氨基)甲基]苯酚（H3L）由4-叔丁基-2,6-二甲醛苯酚与2-氨基苯酚原位合成。该前配体（H3L）与二苯甲酰甲烷（DBMH）或乙酰丙酮（acacH）分别结合镧系元素，可得到具有不同金属原子排布与核数的配合物。以配体L³⁻和二苯甲酰甲烷为原料，成功合成四核配合物{[Dy₄(L)₃(DBM)₄][Et₃NH]}（1）与五核配合物{[Dy₅(μ₃-OH)₂(L)₃(DBM)₄(MeOH)₄]·4(MeOH)}（2）。当以乙酰丙酮为共存配体使用配体L³⁻时，得到四核配合物{[Dy₄(μ₄-OH)­(L)₂(acac)₄(MeOH)₂(EtOH)­(H₂O)]·(NO₃)·2­(MeOH)·3­(EtOH)}（3）以及{[Ln₄(μ₃-OH)₂(L)­(HL)­(acac)₅(H₂O)](HNEt₃)­(NO₃)·2­(Et₂O)}（Ln = Tb（4）、Dy（5）、Ho（6）和Tm（7））。在固态结构中，四核配合物1的金属原子呈线性排布，四核配合物3的金属原子呈方格网状排布，而四核配合物4~7的金属原子呈跷跷板形排布。通过单晶X射线衍射分析（single-crystal X-ray analysis）得到配合物1与3~7的组成，该结果得到电喷雾电离质谱（ESI-MS）的佐证。对配合物1的磁学研究表明其存在弱铁磁相互作用，而配合物2~6的相邻金属中心间存在弱反铁磁相互作用。配合物1、2与3在施加直流磁场（dc field）的条件下均表现出单分子磁体行为（single-molecule magnet behavior）。