Magnetic Exchange in Mn^II[TCNE] (TCNE = Tetracyanoethylene) Molecule-Based Magnets with Two- and Three-Dimensional Magnetic Networks

Abstract

The chemical bond and its role as a mediator of magnetic exchange interaction remains a crucial aspect in the study of molecular magnetism. Within the M[TCNE] (M = 3d metal; TCNE = tetracyanoethylene) class of organic-based magnets, only V [TCNE] x (x ∼ 2) orders magnetically above room temperature (T c ∼ 400 K), while structural factors underlying this exceptional behavior remain elusive. Conversely, Mn-[TCNE] complexes of diverse crystal structure have recently become available, e.g., 2D-layer [Mn(TCNE)(NCMe) 2 ][SbF 6 ] (T c ∼ 75 K), and 3D-network [Mn(TCNE) 1.5 ](I 3 ) 0.5 (T c ∼ 170 K). Using this experimental structural data, DFT simulations have been performed and the spin-polarized electronic structures resolved. The nature of orbital interactions crucial for understanding magnetic behavior was revealed. Magnetic coupling, spin−orbital hybridization, as well as formation of exchange/superexchange pathways have been identified and interpreted in terms of the dimensionality of magnetic interaction. These results illustrate the complex nature of the electron exchange landscape in M[TCNE] molecule-based magnets. ■ INTRODUCTIONFor several decades, magnetism in the solids containing 3d electrons has remained one of the main focuses of modern materials science targeting applications in spintronics. In contrast to the itinerant ferromagnetic exchange between almost free electrons in metals (direct exchange), the main mechanism of exchange interaction in magnetic insulators like simple transition metal oxides is a virtual hopping of electrons between almost isolated ions (metal and oxygen) leading either to anti-or ferromagnetic Heisenberg exchange interaction between unpaired spins of metals, traditionally defined as indirect-or superexchange. 1−3Molecule-based magnets (MBMs) are a relatively new class of magnetic materials, in which molecular moieties bearing unpaired spin density interact electronically and magnetically. 4,5 Compared to conventional metallurgic and ceramic magnets, the main benefits of MBMs are usually associated with their lightweight, mechanical flexibility, tunable color or transparency, low-temperature processing, solubility, and compatibility with polymers and other classes of molecular materials. 6 Furthermore, the use of MBMs in the area of spintronics has the potential to become a disruptive technology, since organic materials can enhance preservation of electron spin orientation lifetime relative to inorganic conductors due to their inherently weak spin−orbit coupling. The M[TCNE] (M = 3d metal; TCNE = tetracyanoethylene) complexes represent one of the most interesting classes of MBMs, possessing numerous compositions and structures with varying dimensionalities of magnetic coupling from one-dimensional (1D) inorganic polymer chains 7 and two-dimensional (2D) layers 8−10 to three-dimensional (3D) networks 11 and amorphous solids. 12 M[TCNE] MBMs exhibit a wide range of magnetic ordering temperatures (T c ), with the highest of 400 K observed in V[TCNE] x (x ∼ 2). 12 Recently, interest...

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Relationship between Site Symmetry, Spin State, and Doping Concentration for Co(II) or Co(III) in β-NaYF4

“…Diluted magnetic oxides and semiconductors, such as cobalt-doped titania and manganese-doped zinc oxide or cadmium selenide, in the form of nanocrystals and quantum dots, represent different patterns of ligand arrangement and crystal-field splitting and exhibit new spectral features contributed by the dopant TM ions . Approaches and results of this work have potential for further application in identification of mechanisms for basic photoinduced processes in magnetically doped quantum dots or molecular magnets for information storage applications. ,, Magnetic molecular crystals and magnetic metalorganic frameworks , also exhibit variable coordination patterns of TM ions to neighboring ligands that may allow the design of new spin-crossover materials.…”

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Magnetic Moment Is an Effective Descriptor for Electrocatalytic Nitrogen Reduction Reaction on Two-Dimensional Organometallic Nanosheets

“…Furthermore, the high electron affinity (2.77 ± 0.09 eV) and strong bonding capacity of TCNE make it particularly amenable to receive electrons. TCNE-based nanostructures have demonstrated interesting motifs, exotic properties, and promising applications. − Lots of articles have reported that TCNE-based materials can be used as molecular magnets for spintronic applications , and as doping molecules to modify the electronic properties for semiconductor applications . Additionally, the TM-tetracyanoquinodimethane (TM-TCNQ), similar to the TM-TCNE system, has been used as an efficient electrocatalyst. , Thus, 2D TCNE-based nanosheets might be good candidates for eNRR.…”