Aminopolyol-Dependent Assembly of Heterometallic Lanthanide–Iron–Oxo Clusters

Lanthanide–iron clusters usually display interesting structures and outstanding magnetic properties. However, due to the high reactivity (acidity) of the Fe³⁺–H₂O bond and the inability to form a terminal oxo ligand, the preparation of high-nuclearity Ln–Fe clusters is a great challenge. Herein, a series of lanthanide–iron–oxo clusters with the formulas [Y₆Fe(HL)₁₀(NO₃)₂(EG)₂(μ₃-OH)₈(H₂O)₄]·ClO₄·N-H₂BDEA·2H₂O (Y₆Fe, 1, H₂L = 3-hydroxypivalic acid, EG = ethylene glycol, N–H₂BDEA = 2,2′-(butylimino)diethanol), [Ln₈Fe₃(H₂TEOA)₂(HTEOA)₂(HL)₁₀(μ₃-OH)₉(μ₂-OH)(μ₄-O)₂(H₂O)₄]·(NO₃)₃·xH₂O (Ln = Y, x = 13 for 2, Y₈Fe₃; Ln = Dy, x = 10 for 3, Dy₈Fe₃; H₃TEOA = triethanolamine), and [Ln₁₂Fe₁₄(HL)₁₆(μ₃-OH)₂₀(μ₂-OH)₁₂(μ₄-O)₁₂(H₂O)₁₂]·(NO₃)₆·xH₂O (Ln = Y, x = 40 for 4, Y₁₂Fe₁₄; Ln = Dy, x = 30 for 5, Dy₁₂Fe₁₄) were obtained by adjusting the pH with different aminopolyols as organic alkalis. Structural analysis showed that a cubane-like unit was the main structural unit in compounds 1–5. Compound 1 was formed by two {Y₃Fe(μ₃-OH)₄} units with the common vertices, and compounds 2 and 3 were formed by two {Y₃Fe(μ₃-OH)₃(μ₄-O)} units with the common vertices bridging a quadrilateral unit {Ln₂Fe₂(μ₃-OH)₃(μ₂-OH)}. The basic structural units of cubane-like {Ln₂Fe₂(μ₃-OH)(μ₄-O)₃}, triangular {LnFe₂(μ₃-OH)₂(μ₄-O)}, and neutral iron–hydroxyl {Fe(μ₃-OH)(μ₂-OH)₂} were found in compounds 4 and 5. The universality of building blocks for the assembly has been demonstrated in high-nuclearity lanthanide–iron–oxo clusters. Meanwhile, the structural regulation of the lanthanide–iron–oxo clusters 1–5 was realized by adjusting the pH with different organic alkalis, which provided the reference for the effective synthesis of high-nuclearity lanthanide–iron–oxo clusters. Magnetic studies showed that 3 and 5 displayed a slow magnetic relaxation behavior.