Designer magnets containing cyanides and nitriles.
TL;DR: Three-dimensional network solids exhibiting magnetic ordering have been made from several first-row metal ions and bridging unsaturated cyanide, tricyanomethanide, and/or dicyanamide ligands, which possess several different structural motifs, and the shorter the bridge, the stronger the interaction.
Abstract: Magnets synthesized from molecules have contributed to the renaissance in the study of magnetic materials. Three-dimensional network solids exhibiting magnetic ordering have been made from several first-row metal ions and bridging unsaturated cyanide, tricyanomethanide, and/or dicyanamide ligands. These materials possess several different structural motifs, and the shorter the bridge, the stronger the interaction (i.e., C⋮N > N⋮CN ≫ N⋮CNC⋮N = N⋮CCC⋮N). Cyanide additionally has the ability to discriminate between C- and N-bonding to form ordered heterobimetallic magnets, and the strong coupling can lead to ferro- or ferrimagnetic ordering substantially above room temperature. Tricoordination of tricyanomethanide results in spin-frustrated systems, which possess interpenetrating rutile-like networks. In contrast, single rutile-like frameworks are formed by μ3-bonded dicyanamide, which leads to ferromagnetics and weak ferromagnetics.
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TL;DR: In this paper, a review of the physical measurements made on the α-M(dca)2 series is given, together with interpretations for the different net exchange coupling and consequent 3D order.
959 citations
TL;DR: This critical review provides an overview of the various framework-structured weak ferromagnets based on different grades of ligands (from mono-atom to three-atom-like ligands) and the relationships between structural features and the properties, rational employment of the ligands, andWeak ferromagnetic strategies for molecule-based magnets with exciting properties and applications.
Abstract: Framework-structured weak ferromagnets are new rising stars in molecule-based magnetic materials. The framework structures are powerful carriers for long-range ordering of spins. And weak ferromagnetism due to spin canting is an effective approach for magnets because of its frequent occurrence and desired spontaneous magnetization as long as the canting angle γ is large enough. In this critical review, we provide an overview of the various framework-structured weak ferromagnets based on different grades of ligands (from mono-atom to three-atom-like ligands). Particular emphasis is given to the relationships between structural features and the properties, rational employment of the ligands, and weak ferromagnetic strategies for molecule-based magnets with exciting properties and applications (273 references).
363 citations
TL;DR: A review of recent advances in α-alkylation reactions based on hydrogen borrowing methodologies using alcohol as an alkylating agent is provided in this article, with a focus on highly practical and green chemistry approaches involving modified catalytic systems, including metal-supported heterogeneous catalysts and nanoparticle-based catalysts.
Abstract: This paper summarizes recent advances in α-alkylation reactions based on hydrogen borrowing methodologies using alcohol as an alkylating agent. This review provides a summary of recent progress toward the α-alkylation of carbonyl substrates, as well as relatively unactivated substrates bearing fewer acidic α-hydrogens, such as acetonitriles, acetamides, esters, methylpyrimidines, and methylquinolines. A summary of recent improvements in α-methylation strategies based on hydrogen borrowing methodologies has also been provided. Particular emphasis has been placed on highly practical and green chemistry approaches involving modified catalytic systems, including metal-supported heterogeneous catalysts and nanoparticle-based catalysts, as well as reactions conducted in the absence of a transition-metal catalyst. A review of recent achievements in methylation strategies using methanol as a methyl source, and their application to the α-methylation of ketones using transition-metal catalyzed hydrogen borrowing me...
349 citations
TL;DR: These magnetically ordered materials are reviewed from a perspective of the structural dimensionality after a discussion of the important aspects of magnetism pertaining to molecule-based magnets, including the determination of the magnetic ordering temperature (T(c).
Abstract: Magnets composed of molecular components that provide both electron spins and spin-coupling pathways can stabilize bulk magnetic ordering. This was first reported for the ionic, zero-dimensional (0-D) electron transfer salt [Fe(C5Me5)2]+[TCNE]˙− (TCNE = tetracyanoethylene), which orders as a ferromagnet at Tc = 4.8 K. Later V[TCNE]x (x ∼ 2) was characterized to order above room temperature at 400 K (127 °C). Subsequently, numerous examples of organic- and molecule-based magnets have been characterized. In this critical review, after a discussion of the important aspects of magnetism pertaining to molecule-based magnets, including the determination of the magnetic ordering temperature (Tc) these magnetically ordered materials are reviewed from a perspective of the structural dimensionality (208 references).
336 citations
TL;DR: Recent developments in the employment of DMF in the fields of formylation, aminocarbonylation, amination, amidation, and cyanation, as well as its reaction with arynes are summarized.
Abstract: Often used as a common solvent for chemical reations and utilized widely in industry as a reagent, N,N-dimethylformamide (DMF) has played an important role in organic synthesis for a long time. Numerous highly useful articles and reviews discussing its utilizations have been published. With a focus on the performance of DMF as a multipurpose precursor for various units in numerous reactions, this Minireview summarizes recent developments in the employment of DMF in the fields of formylation, aminocarbonylation, amination, amidation, and cyanation, as well as its reaction with arynes.
315 citations
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TL;DR: In this paper, a metal-organic framework was designed to bind aromatic guest molecules selectively, and the inclusions can be selectively readsorbed, even after the removal of included guest molecules, and they showed that the crystal lattice was thermally stable up to 350 °C.
Abstract: MICROPOROUS inorganic materials such as zeolites find widespread application in heterogeneous catalysis, adsorption and ion-exchange processes. The rigidity and stability of such frameworks allow for shape- and size-selective inclusion of organic molecules and ions1–4. Analogous microporous structures based on organic building blocks have the potential for more precise rational design, through control of the shape, size and functionalization of the pores5–8. Here we report the synthesis of a metal–organic framework designed to bind aromatic guest molecules selectively. The basic building block is a symmetric organic molecule, which binds metal ions9,10 to form layers of the metal–organic compound alternating with layers whose composition is determined by the functionalization of the starting molecules. The layers create channels in which guest aromatic molecules may be selectively bound. We show that the crystal lattice thus formed is thermally stable up to 350 °C, even after removal of included guest molecules, and that the inclusions can be selectively readsorbed.
2,094 citations
1,641 citations
TL;DR: In this paper, a room-temperature organometallic magnet was synthesized by combining a hexa-cyanometalate [M(CN)6]q− with a Lewis acid Lp+.
Abstract: THE rational design of molecular compounds that exhibit spontaneous magnetic ordering might enable one to tailor magnetic properties for specific applications in magnetic memory devices1–4. In such materials synthesized previously5–17, however, the underlying weak magnetic interactions are incapable of maintaining ordering at ambient temperatures. One remarkable exception is a compound derived from vanadium and tetracyanoethylene18, but the material is amorphous and fragile, and consequently the molecular interactions responsible for its striking properties are not understood. Here we demonstrate another route to the synthesis of a room-temperature organometallic magnet, in which we combine a hexa-cyanometalate [M(CN)6]q− with a Lewis acid Lp+ If L and M are transition-metal ions, then the orbital interactions in the resulting compound can be described by well understood principles21–24, and it is therefore possible to choose the metals to tune the compound's magnetic properties–in particular, the magnetic ordering (Curie) temperature Tc (refs 21–26). We have synthesized a room-temperature magnetic material (TC = 315 K) that belongs to the Prussian blue family of compounds27 (where M is chromium and L is vanadium), demonstrating that transition-metal hexacyano complexes are promising components for the construction of molecule-based high-Tc magnets.
1,389 citations
TL;DR: The study of cooperative phenomena in magnetism has provided fertile ground for testing theories of interacting systems that possess different spatial dimensions, ranges, and sign of interactions, and that exhibit local anisotropy of the basic interacting unit, the magnetic spin this paper.
Abstract: The study of cooperative phenomena in magnetism has provided fertile ground for testing theories of interacting systems that possess different spatial dimensions, ranges, and sign of interactions, and that exhibit local anisotropy of the basic interacting unit, the magnetic spin. This study has also motivated the development of new classes of materials, from the oldest known type of magnets, namely ferromagnets, to modern substances embodied in the unusual random field and spin glass compounds. In this context, we use the term material class to mean a set of compounds that share both microscopic, as well as macroscopic, or bulk, properties. Thus for example, ferro magnets possess the microscopic uniform ferromagnetic type exchange or dipolar interaction between spins, in addition to a bulk low temperature magnetization approaching the theoretical saturated moment value, and characteristic critical behavior at the Curie, or order ing, temperature. Among the known classes of magnets, spin glasses are among the most fascinating, displaying in their bulk properties simul taneous sharp ordering features in their magnetic response while exhibiting no such anomalies in their thermal response (1). These properties are thought to arise from a ground state characterized not by a single potential well representing the uniform arrangement of perfectly ordered spins, as in a ferromagnet, but rather by an energy landscape with many nearly degenerate ground state configurations separated by barriers of random height ( 1 ). The microscopic parameters empirically associated with spin glass
1,293 citations
TL;DR: In this paper, the use of sol-gel methods was described to synthesize several crystalline molecule-based magnets with the Prussian blue structure, including KV II[CrIII (CN)6]‚2H2O, with an ordering temperature of 376 K (103°C).
Abstract: Recently, there has been much interest in the synthesis of molecule-based magnets, which are magnets whose solid-state structures consist of arrays of molecular units. 1,2 Such solids do not at present have real-world uses, in part because none of them possesses a key characteristic: for most commercial applications, a magnet must retain its magnetism well above room temperature. Of the four molecule-based magnets that remain magnetic at room temperature, one decomposes at 350 K, 3 and three demagnetize near 315 K. 4,5 All four of these solids are amorphous, and their solid state structures are unknown, although the latter three probably adopt a structure like that of the pigment Prussian blue. We now describe the use of sol -gel methods to synthesize several crystalline molecule-based magnets with the Prussian blue structure. The gelation process appears to be important to the growth of the crystalline phase. Most notable among the current results is the discovery of a molecule-based magnet, KV II[CrIII (CN)6]‚2H2O, with the unprecedented magnetic ordering temperature of 376 K (103°C). The four known molecule-based magnets that keep their magnetism at room temperature are listed below, along with the temperatures at which the magnetism is lost:
619 citations