Organic and Organometallic Molecular Magnetic Materials—Designer Magnets

Abstract

Magnets composed of molecular species or polymers and prepared by relatively low‐temperature organic synthetic methodologies are a focus of contemporary materials science research. The anticipated properties of such molecular‐species‐based magnetic materials, particularly in combination with other properties associated with molecules and polymers, may enable their use in future generations of electronic, magnetic, and/or photonic/photronic devices ranging from information storage and magnetic imaging to static and low‐frequency magnetic shielding. A tutorial of typical magnetic behavior of molecular materials is presented. The three distinct models (intramolecular spin coupling through orthogonal orbitals in the same spatial region within a molecule/ion, intermolecular spin coupling through pairwise “configuration interaction” between spin‐containing moieties, and dipole—dipole, through‐space interactions) which enable the design of new molecular‐based magnetic materials are discussed. To achieve the required spin couplings for bulk ferro‐ or ferrimagnetic behavior it is crucial to prepare materials with the necessary primary, secondary, and tertiary structures akin to proteins. Selected results from the worldwide effort aimed at preparing molecular‐based magnetic materials by these mechanisms are described. Some organometallic solids comprised of linear chains of alternating metallocenium donors (D) and cyanocarbon acceptors (A) that is, …︁D•+ A•− D•+ A•−…︁, exhibit cooperative magnetic phenomena. Bulk ferromagnetic behavior was first observed below the critical (Curie) temperature Tc of 4.8 K for [FeIII(C5Me5)2]•+ [TCNE]•− (Me = methyl; TCNE = tetracyanoethylene). Replacement of FeIII with MnIII leads to a ferromagnet with a Tc of 8.8 K in agreement with mean‐field models developed for this class of materials. Replacement with CrIII, however, leads to a ferromagnet with a Tc lowered to 3.65 K which is at variance with this model. Extension to the reaction of a vanadium(o) complex with TCNE leads to the isolation of a magnet with a Tc ≈ 400 K, which exceeds the thermal decomposition temperature of the material. This demonstrates that a magnetic material with a Tc substantially above room temperature is achievable in a molecule/organic/polymeric material. Finally, a new class of one‐dimensional ferrimagnetic materials based on metalloporphins is discussed.

Full-potential linearized augmented plane-wave method for one-dimensional systems: Gold nanowire and iron monowires in a gold tube

“…Molecular magnets with a tendency towards one-dimensionalization are synthesized and experimentally observed as quasi-1D structures showing intriguing magnetic and structural properties. 18,19 In order to understand the structure-property relation in these new materials on the basis of the electronic structure, ab initio calculations based on the density functional theory play an important role. The low-dimensionality, the chemical complexity, the open structure, and the large variety of chemical elements in these systems ask for flexible ab initio methods, which can cope with these issues.…”

Room-temperature organic-based spin polarizer

“…9 The development of organic-based magnets is promising to provide a pathway to circumvent this problem. 10 The combination of organic magnets and organic semiconductors will also be likely to give rise the next-generation lightweight, mechanically flexible and low-cost spintronic devices.…”

Magnetic Specific Heat of Anion-Radical Salt [Ni(bipy)3](TCNQ)4·(CH3)2CO at Very Low Temperatures

“…These compounds are able to form low-dimensional magnets, and the arrangements of the ARS complexes have considerable impact on the charge transfer and magnetic properties. Materials formed by a connection of metal ions and organic radicals in a crystal structure can combine the properties of organic and inorganic components that can be used in various applications [1][2][3][4][5][6].…”