Metal–Organic Frameworks as Playgrounds for Reticulate Single-Molecule Magnets

• Published in: Inorganic chemistry 2019-11, Vol.58 (21), p.14498-14506
• Main Authors: Kalinke, Lucas H. G, Cangussu, Danielle, Mon, Marta, Bruno, Rosaria, Tiburcio, Estefania, Lloret, Francesc, Armentano, Donatella, Pardo, Emilio, Ferrando-Soria, Jesus
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b02086

Achieving fine control on the structure of metal–organic frameworks (MOFs) is mandatory to obtain target physical properties. Herein, we present how the combination of a metalloligand approach and a postsynthetic method is a suitable and highly useful synthetic strategy to success on this extremely difficult task. First, a novel oxamato-based tetranuclear cobalt­(III) compound with a tetrahedron-shaped geometry is used, for the first time, as the metalloligand toward calcium­(II) metal ions to lead to a diamagnetic CaII–CoIII three-dimensional (3D) MOF (1). In a second stage, in a single-crystal-to-single-crystal manner, the calcium­(II) ions are replaced by terbium­(III), dysprosium­(III), holmium­(III), and erbium­(III) ions to yield four isostructural novel LnIII–CoIII [Ln = Tb (2), Dy (3), Ho (4), and Er (5)] 3D MOFs. Direct-current magnetic properties for 2–5 show typical performances for the ground-state terms of the lanthanoid cations [7F6 (TbIII), 6H15/2 (DyIII), 5I8 (HoIII), and 4I15/2 (ErIII)]. Analysis of the χM T data indicates that the ground state is the lowest M J value, that is, M J = 0 (2 and 4) and ±1/2 (3 and 5). Kramers’ ions (3 and 5) exhibit field-induced emergent frequency-dependent alternating-current magnetic susceptibility signals, which is indicative of the presence of slow magnetic relaxation typical of single-molecule magnets.