Unravelling interplay between molecule-based spin-state switching and electron transport in a single-crystal 3D metal-organic framework (original) (raw)
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A Molecule-Based Nanoporous Material Showing Tuneable Spin-Crossover Behavior near Room Temperature
Advanced Materials, 2007
One of the great challenges underlying the search for molecule-based functional materials is to produce systems exhibiting properties of technological interest that can be tuned and exploited at room temperature. Some landmark achievements in this respect are the discovery of a molecule-based magnet that displays ordering above 300°C, and the preparation of molecular materials that undergo spin-crossover phenomena near room temperature. Spin-crossover materials are based on the ability of certain transition metal ions to interconvert between two labile electronic states with concomitant switching of their color, magnetic properties, and/or molecular structural parameters. The transition is triggered by external stimuli, such as electromagnetic radiation, magnetic fields, or pressure/temperature variations. Within crystalline phases, the response to the spin-crossover may be transmitted in a cooperative manner throughout the material, leading to a hysteretic behavior. In such a case, the system becomes bistable and can therefore be considered as an externally addressable molecular switch. Current efforts are aimed at integrating spin-crossover centers into metal organic frameworks (MOFs) to combine the properties derived from the spin transition with other properties, such as chirality, conductivity or those derived from nanoporosity. The molecular approach used in preparing hybrid materials has been mostly exploited to obtain networks that exhibit a wide range of pore sizes and shapes, with the added potential of offering a variety of other functions, in particular because of the inclusion of transition metals. This may lead to systems where the multifunctionality is manifested by the coexistence of more than one property, such as ferromagnetism and metal conductivity, with no mutual interdependence. The presence of different functions within a material, however, can occur in such a way that they influence each other in a synergistic manner, thereby producing effects that would not be observed if these properties were not coupled. Remarkable examples are, for instance, the observation of a switchable dielectric constant in a material controlled by the spin state of its spin-crossover centers, or the ability to modify the spin-crossover properties of a nanoporous framework by changing the nature of its guest molecules. We have been engaged for some time in the design and synthesis of sophisticated multidentate N-heterocyclic ligands such as 2,4,6-tris-(di(pyridin-2-yl)amino)-1,3,5-triazine (dpyatriz; Scheme S1), and have studied their ability to combine with paramagnetic ions in the construction of zerodimensional or polymeric metal-organic arrays with interesting magnetic properties. For example, metal-organic open frameworks with unprecedented structures, and which include open-shell metals, have been fully characterized. In addition, discrete dinuclear complexes of Fe II with dpyatriz have been obtained, and display (extremely rare) ferromagnetic exchange, or spin-crossover properties that can be easily modulated by changing the solvent, which acts as a terminal ligand. The use of such dimeric units as building blocks in solvothermal reactions involving Fe II has now taken us one step further, providing access to a new metalorganic nanoporous material that exhibits room-temperature spin-crossover behavior. The structure of this material can be modified reversibly through exposure to various solvents; the transformation leading to significant changes to the spin-transition properties. The porosity of the material enables the solvent exchange and is thus responsible for the COMMUNICATION
Charge transport in metal–organic frameworks for electronics applications
APL Materials, 2020
In recent years, functional electronic nanomaterials have made significant strides from advancements in the interplay of physics, chemistry, materials science, and computational research. However, synthetically tunable electronic materials are a long-standing, but elusive, technological goal. More recently, metal-organic frameworks (MOFs), a class of nanoporous, hybrid inorganic-organic crystalline solids, have garnered attention as a novel class of electronic nanomaterials. The aim of this perspective is to (i) highlight the charge transport behavior of recently discovered (2017-2019) electronic MOFs and (ii) recommend future directions for improvement of intrinsically and extrinsically conductive MOFs for MOF-based electronics.
Journal of the American Chemical Society, 2015
A three-dimensional network solid composed of Fe(III) centers and paramagnetic semiquinoid linkers, (NBu4)2Fe(III)2(dhbq)3 (dhbq(2-/3-) = 2,5-dioxidobenzoquinone/1,2-dioxido-4,5-semiquinone), is shown to exhibit a conductivity of 0.16 ± 0.01 S/cm at 298 K, one of the highest values yet observed for a metal-organic framework. The origin of this electronic conductivity is determined to be ligand mixed-valency, which is characterized using a suite of spectroscopic techniques, slow-scan cyclic voltammetry, and variable-temperature conductivity and magnetic susceptibility measurements. Importantly, UV-Vis-NIR diffuse reflectance measurements reveal the first observation of Robin-Day Class II/III mixed valency in a metal-organic framework. Pursuit of stoichiometric control over the ligand redox states resulted in synthesis of the reduced framework material Na0.9(NBu4)1.8Fe(III)2(dhbq)3. Differences in electronic conductivity and magnetic ordering temperature between the two compounds are ...
Spin-dependent transport in organic-ferromagnets
The European Physical Journal B, 2009
Based on the modified Su-Schrieffer-Heeger model and the non-equilibrium Green's function current formula, the spin polarization of the ferromagnet-electrode connected organic ferromagnet is theoretically studied. The spin polarization can be suppressed by atomic dimerization and be driven by an applied electric field. We investigate the spin polarization from the viewpoint of energy competitions in different interactions under the electric field. In addition, the ferromagnetic electrodes significantly enhance the spin polarization.
Bidirectional Chemo-Switching of Spin State in a Microporous Framework
Angewandte Chemie International Edition, 2009
Porous coordination polymers (PCPs) have appeared in the past decade as a new class of porous materials providing permanent and designable regular microporosity through flexible coordination bonds. Compared with existing inorganic porous materials, PCPs provide significant enhancement in flexibility and in the dynamics of their frameworks. This versatility has created prospects for applications in gas storage, gas separation, and heterogeneous catalysis. The next generation of PCPs is being conceived to switch various solidstate properties (e.g., optics, conductivity, or magnetism) through guest adsorption processes, which resemble, in a simplified form, the conversion process from chemical stimulus to information signal in the chemosensory organs for taste and smell. Herein, the chemical response of the framework would be crucial for producing drastic physicochemical changes. To implement such chemoresponsive switching at ordinary temperatures we focused on coupling the porous properties and the spin-crossover (SCO) phenomenon. SCO is well known in iron(II) coordination compounds, whose electron configurations can move between high-spin (HS) and low-spin (LS) states under external perturbations (temperature, pressure, and light irradiation), producing changes in magnetic, optical, dielectric, and structural properties. [7][10] In special cases, this switch can be performed within the hysteresis loop based on the first-order spin transition (ST). Although several compounds have been reported as PCPs incorporating SCO subunits (SCO-PCPs), these materials do not display a room temperature first-order hysteretic spin transition, [10] the guest adsorption and SCO being essentially disconnected events. In these SCO-PCPs, adsorption of guest molecules induces an incomplete and gradual spin transition at low temperature. Even now, strategies for the direct coupling of porous properties and magnetic switching are still underdeveloped.
Spin Transport in Organic Semiconductors: A Brief Overview of the First Eight Years
arXiv: Mesoscale and Nanoscale Physics, 2011
In this article we briefly review the current state of the experimental research on spin polarized transport in organic semiconductors. These systems, which include small molecular weight compounds and polymers, are central in the rapidly maturing area of organic electronics. A great deal of effort has been invested in the last eight years toward understanding spin injection and transport in organics. These developments have opened up the possibility of realizing a new family of organic spintronic devices which will blend the chemical versatility of organic materials with spintronic functionalities.
Spin transport in organics and organic spin devices
IEE Proceedings - Circuits, Devices and Systems, 2005
The authors present a theory to describe spin transport across a polymer sandwiched between magnetic contacts and propose organic spin devices based on this theory. It is found that even a weak magnetic field can significantly modify spin transport in polymers through spin precession. This sensitivity can be exploited to design ultrasensitive magnetometers and low-power magnetic-field-effect transistors. It is shown that, at room temperature, the organic magnetometers are capable of detecting sub-nanotesla magnetic fields, and the I-V characteristics of the magneticfield-effect transistors can be strongly modified by magnetic fields of a few gauss with response times of a few nanoseconds.
Nature Communications, 2020
The incorporation of metal-organic frameworks into advanced devices remains a desirable goal, but progress is hindered by difficulties in preparing large crystalline metal-organic framework films with suitable electronic performance. We demonstrate the direct growth of large-area, high quality, and phase pure single metal-organic framework crystals through chemical vapor deposition of a dimolybdenum paddlewheel precursor, Mo2(INA)4. These exceptionally uniform, high quality crystals cover areas up to 8600 µm2 and can be grown down to thicknesses of 30 nm. Moreover, scanning tunneling microscopy indicates that the Mo2(INA)4 clusters assemble into a two-dimensional, single-layer framework. Devices are readily fabricated from single vapor-phase grown crystals and exhibit reversible 8-fold changes in conductivity upon illumination at modest powers. Moreover, we identify vapor-induced single crystal transitions that are reversible and responsible for 30-fold changes in conductivity of th...
Reversible Switching of Organic Diradical Character via Iron-Based Spin-crossover
2020
Organic diradicals are uncommon species that have been intensely studied for their unique properties and potential applicability in a diverse range of innovative fields. While there is a growing class of stable and well characterized organic diradicals, there has been recent focus on how diradical character can be controlled or modulated with external stimuli. Here we demonstrate that a diiron complex bridged by the doubly oxidized ligand tetrathiafulvalene-2,3,6,7tetrathiolate (TTFtt 2−) undergoes a thermally induced Fe-centered spin-crossover which yields significant diradical character on TTFtt 2−. UV-vis-Near-IR, Mössbauer, NMR, and EPR spectroscopies with magnetometry, crystallography, and advanced theoretical treatments suggest that this diradical character arises from a shrinking TTFtt 2− π-manifold from the Fe(II)-centered spin-crossover. The TTFtt 2− centered diradical is predicted to have a singlet ground state by theory and variable temperature EPR. This unusual phenomenon demonstrates that inorganic spin transitions can be used to modulate organic diradical character. Results and Discussion Synthesis and Structural Parameters Complex 1 was synthesized via reaction with the deprotected proligand 2,3,6,7-tetrakis(2cyanoethylthio)tetrathiafulvalene (TTFtt(C2H4CN)4) in good yield. Complex 1 was insoluble in all solvents we investigated which precluded detailed characterization but is pure as indicated by combustion analysis and behaves as a suitable synthon for subsequent chemistry. Complex 1 can be doubly oxidized with [Cp2Fe][BAr F 4] to form 2 which is more soluble, enabling common solution characterization including 1 H NMR and cyclic voltammetry measurements (Figure S1-S2). Oxidation from 1 to 2 could be ligandcentered (TTFtt 4− →TTFtt 2−), metal-centered (2 Fe(II)→2 Fe(III)), or some intermediate case, but the data acquired for 2 supports a TTFtt 2− structure arising from ligandcentered oxidation (Chart 1B, see below). Compound 2 was structurally characterized via singlecrystal X-ray diffraction (SXRD) at 293 K (2-HT; Figure S3) and 100 K (2-LT; Figure 1). In both structures TTFtt 2− is bridged between two TPA-capped Fe centers with two outer-sphere BAr F 4 − counter anions. The most striking difference between these temperatures is markedly longer Fe bond lengths in 2-HT. The Fe-Npyridine and Fe-Namine bond lengths in 2-LT are 1.958(6)-1.979(6) and 2.017(6) Å (Figure 1), respectively. These values are consistent with Fe-N bonds in other low-spin complexes with a Fe-TPA moiety. 16,17 In 2-HT, these bonds are 0.18-0.19 and 0.244(11) Å longer than their counterparts at 100 K, respectively, and are consistent with high-spin Fe-TPA complexes. The shorter Fe bonds at lower temperature indicate that 2 exhibits a temperature dependent spincrossover as observed in related compounds. 16,21