Metal–Organic Framework Magnets

Abstract

Metal–organic frameworks represent the ultimate chemical platform on which to develop a new generation of designer magnets. In contrast to the inorganic solids that have dominated permanent magnet technology for decades, metal–organic frameworks offer numerous advantages, most notably the nearly infinite chemical space through which to synthesize predesigned and tunable structures with controllable properties. Moreover, the presence of a rigid, crystalline structure based on organic linkers enables the potential for permanent porosity and postsynthetic chemical modification of the inorganic and organic components. Despite these attributes, the realization of metal–organic magnets with high ordering temperatures represents a formidable challenge, owing largely to the typically weak magnetic exchange coupling mediated through organic linkers. Nevertheless, recent years have seen a number of exciting advances involving frameworks based on a wide range of metal ions and organic linkers. This review provides a survey of structurally characterized metal–organic frameworks that have been shown to exhibit magnetic order. Section 1 outlines the need for new magnets and the potential role of metal–organic frameworks toward that end, and it briefly introduces the classes of magnets and the experimental methods used to characterize them. Section 2 describes early milestones and key advances in metal–organic magnet research that laid the foundation for structurally characterized metal–organic framework magnets. Sections 3 and 4 then outline the literature of metal–organic framework magnets based on diamagnetic and radical organic linkers, respectively. Finally, Section 5 concludes with some potential strategies for increasing the ordering temperatures of metal–organic framework magnets while maintaining structural integrity and additional function.

Magnetic Ordering via Itinerant Ferromagnetism in a Metal-Organic Framework

“…11,12,27,28 The variable-field magnetization data collected between 3 and 270 K exhibit an S-shaped curve that quickly saturates at a magnetization of 2.39 µB mol −1 at 3 K, close to the expected value of 2.33 µB mol −1 for ferromagnetically coupled low-spin CrII and Cr III centers present in a 2:1 ratio(Fig. 3b).…”

Electroactive Organic Building Blocks for the Chemical Design of Functional Porous Frameworks (MOFs and COFs) in Electronics

“…Synthetic methodologies based on bottom-up or top-down approaches need also to be taken into account to obtain MOFs and COFs as bulk or single-/fewlayer materials, which have ad irecti nfluence on their physical properties. [17,18] Besides their inherent porosity,M OFs and COFs may also incorporate electronic functionalities such as electrical conductivity, [19][20][21] luminescence [22][23][24][25] or magnetism, [26,27] which strongly depend on the electronic nature of the selected building blocks, becoming very attractive for their implementation as integral components in electronic ando ptoelectronic devices. [28][29][30] Indeed, the first examples of MOF-and COF-based chemiresistive sensors, [31,32] field-effect transistors, [33][34][35] thermoelectric materials, [36,37] and supercapacitors [38,39] have been reported recently.S uch porous materials may present certain additional advantages, including the easy modulation of their physicalp roperties by post-synthetic modifications or by incorporation of guest molecules, and the fine-tuning of their electronic performance is easily accomplished.…”

A Three‐Dimensional Pentanuclear Co(II) Coordination Polymer: Structural Topology, Hirshfeld Surface Analysis and Magnetic Properties

“…[9,10] The magnetic materials derived from these CPs are highly preferred over the traditional inorganic magnets due to their structural tenability and electronic versatilities. [11,12] Consequently, the factors prevailing the magnetic anisotropy in transition metal complexes is very important owing to its strong first order spin-orbit coupling displayed by the metal ion in + 2 oxidation state. [13,14] Polynuclear Co II based frameworks are particular interest because of the potential source of anisotropy that the Co II ions may provide, in which ferromagnetic or antiferromagnetic coupling may be witnessed.…”

“… [9,10] . The magnetic materials derived from these CPs are highly preferred over the traditional inorganic magnets due to their structural tenability and electronic versatilities [11,12] . Consequently, the factors prevailing the magnetic anisotropy in transition metal complexes is very important owing to its strong first order spin‐orbit coupling displayed by the metal ion in +2 oxidation state [13,14] .…”