1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

/pdf/chemical-redox-agents-for-organometallic-chemistry-4fs84ntwp8.pdf

Chemical Redox Agents for Organometallic Chemistry

Crystal Engineering and Organometallic Architecture.

Molecule-based materials with active physical properties, in particular electrical, magnetic, and optical, are a focus of contemporary materials chemistry research. Certainly, one reason for this interest has been the realization that these materials can exhibit cooperative properties typically associated with the inorganic network solids, as for example metallic conduction or even superconductivity,1 ferromagnetism,2 and nonlinear optical properties.3 With respect to the electrical properties, many important achievements were obtained in the 1970s with the discovery of the first molecule-based metal in 1972,4 namely the π-electron donor-acceptor complex [TTF][TCNQ] (TTF ) tetrathiafulvalene, TCNQ ) tetracyano-p-quinodimethane),5 and the report of the first molecule-based superconductors in 1979 based on the Bechgaard salts [TMTSF]2X (X ) PF6, AsF6; TMTSF ) tetramethyltetraselenafulvalene).6 The recognition of molecule-based ferromagnetic compounds is more recent and has emerged only in the past decade with the discovery of the electron-transfer salt [Fe(C5Me5)2][TCNE] (TCNE ) tetracyanoethylene) in 1985.7 Since these pioneering studies, the two areassmolecule-based metals and magnetsshave witnessed rapid development, and many new molecules have been designed which, if assembled in the appropriate manner in the solid, will enable researchers to improve the physical properties by increasing superconducting and ferromagnetic critical temperatures. A current development in the general area of molecule-based materials is to design, from a wise choice of the constituent molecules, new materials that combine properties not normally associated with a single material. Some intriguing applications of this concept would be to couple conductivity or optical phenomena with magnetic properties. In fact, this challenging goal was proposed8 in the mid-1980s but has only recently begun to be explored. Efforts in this direction nucleated with the design of hybrid materials formed by two molecular networks, such as anion/cation salts or host/guest solids, where each network furnishes distinct physical properties. In these new types of materials, each network contributes distinct physical properties to the solid. Examples include hybrid molecule-based materials, combining inorganic metal complexes that act as structural or magnetic components with an organic π-electron donor or acceptor molecule that furnishes the pathway for electronic conductivity.9 Polyoxometalates have been found to be extremely versatile inorganic building blocks for the construction of the aforementioned functionally active solids.10 The present article highlights recent results and provides a perspective of the use of polyoxometalates in the construction of molecule-based materials. We present herein the different classes of polyoxometalate-based hybrid materials that are of considerable interest due to their electrical or/and magnetic properties. These are (i) organic/inorganic hybrid salts in which the electron donors are organic molecules of the TTF type, (ii) organometallic/inorganic salts in which the electron donor is the decamethylferrocene complex, and (iii) organic/inorganic films in 273 Chem. Rev. 1998, 98, 273−296

http://www1.udel.edu/chem/polenova/PDF/Polyoxometalates/POM_materials_ChemRev1998.pdf

Polyoxometalate-Based Molecular Materials

Triazoles and tetrazoles: Prime ligands to generate remarkable coordination materials

Molecular materials are characterized by being made up by discrete molecules. This structural property gives in principle many possibilities, to modulate the bulk electrical, magnetic, and optical properties of the material by choosing appropriately the constituent molecules. At the same time, however, it is a challenge to develop synthetic strategies that allow the control of the spatial distribution of the molecules in the lattice. In fact, the bulk properties are always determined by cooperative interactions between the constituent molecules, which consequently must be assembled in the lattice in such a way as to maximize the bulk response. In this Account we provide a concise resume of magnetic phenomena, report briefly on the different strategies that have been developed up to the moment for designing molecular magnetic materials, and then summarize our own approach and the main results that have been obtained in this area.

Toward molecular magnets: The metal-radical approach

Structural and magnetic characterization of electron-transfer salts of hexacyanotrimethylenecyclopropanide, {C3[C(CN)2]3}.bul.- and [Fe(C5Me5)2].bul.+ (1:1; two phases) and [Fe(C6H3Me3)2]2+ (1:2). Evidence for 1-D antiferromagnetic behavior in segregated {Fe(C5Me5)2].bul.+ chains

The title ligand (hereafter LL), is found to form an exciting new series of pseudo-octahedral Fe(II) compounds with formula Fe(LL)3X2. N Solvent, which exhibit conveniently studied spin-crossover transformations between nominal5T and1A states of Fe(II). Mossbauer spectra indicate that the spin-crossover transformations for these new systems are probably of the continuous type. There is considerable variation in the degree of conversion to low spin with decreasing temperature depending on gegen ion, solvation and/or location of methyl substituent on the triazole - ligand. The Mossbauer spectra for particular complexes in this group show an absence of both noticeable hysteresis and mechanical grinding effects.

Spin-crossover behavior in a new series of iron (II) compounds based on the ligand 5-(2-pyridyl)-1,2,4-triazole

Observation of a Weak Ferromagnetic Ground State Structure for the Lithium-Insertion Compound Li2Fe2(MoO4)3

The crystal structure of the title compound, FeTAB, has been determined by X-ray diffraction and has been found to be isomorphous to that of the chloride analogue, FeTAC. The low-temperature magnetic susceptibility of polycrystalline samples can be modeled by using a one-dimensional ferromagnetic Ising model with a molecular field correction. The exchange parameters are estimated to be J/k=4 K and z'J'/k=−0.2 K, indicating that FeTAB has an intrachain exchange constant only one-fourth of that found in the chloride analogue while the interchain interactions are more than 10-time greater. Antiferromagnetic ordering is observed in the Mossbauer spectra near 1.3 K

J. H. Zhang

Papers

Structural and magnetic characterization of electron-transfer salts of hexacyanotrimethylenecyclopropanide, {C3[C(CN)2]3}.bul.- and [Fe(C5Me5)2].bul.+ (1:1; two phases) and [Fe(C6H3Me3)2]2+ (1:2). Evidence for 1-D antiferromagnetic behavior in segregated {Fe(C5Me5)2].bul.+ chains

Spin-crossover behavior in a new series of iron (II) compounds based on the ligand 5-(2-pyridyl)-1,2,4-triazole

Observation of a Weak Ferromagnetic Ground State Structure for the Lithium-Insertion Compound Li2Fe2(MoO4)3

A bromide analog of a one-dimensional Ising ferromagnet: trimethylammonium catena-bis(.mu.-bromo)diaquoiron(II) bromide

Further study of the low-temperature magnetic properties of the complex bimetallic salt hexaamminecobalt hexachloroferrate(3-)