bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cluster Compounds: Inorganometallic Compounds Containing Transition Metal & Main Group Elements
Authors: Fehlner Thomas P. 
Published: December 2011

Abstract
The relationships between p‐block element cages and d‐block element clusters, as evidenced by the structures and properties of mixed main group–transition metal compounds, are explored. After a review of the cluster‐bonding characteristics of main group and transition metal homonuclear clusters, including the role of hydrogen atoms and internal or external ‘ligand’ fragments, the related but more complex behavior of main group–transition metal clusters is illustrated. The emphasis is on how the competition between the fundamental bonding properties of p‐block and d‐block elements is expressed in geometric and electronic structure as well as reactivity. Thus, for a limited number of cluster shapes, examples of known compounds are compiled, thereby illustrating the convenience of the cluster versus metal–ligand view as well as outlining the numerous compounds yet to be synthesized and evaluated. Finally, the reactivity of these ‘inorganometallic’ clusters is illustrated. Not only are examples analogous to those found in the homonuclear systems given but so also are examples of unexpected reactivity generated by the synergistic main group–transition metal network.
Intercalation Chemistry
Authors: Jacobson Allan J. , Nazar Linda F. 
Published: December 2011

AbstractThe term ‘intercalation’ refers to a process whereby a guest molecule or ion is inserted into a host lattice. The structure of the guest–host or intercalation compound is only slightly perturbed from the host structure and the reaction used to form the compound is reversible.In this chapter, the major classes of host lattice are classified by both dimensionality and electronic properties. In three‐dimensional systems, the sizes of the guest species are constrained by the dimensions of the host lattice. In lower dimensional systems, no such restriction exists and the strongly bonded layers or chains can adjust their separation freely to accommodate guest species of different sizes. With increasing guest size, the structural correlation between layers or chains is diminished and in the limiting case, complete separation of single layers or chains occurs in solution, resulting in the formation of colloidal dispersions.Insulating host lattices undergo reactions that involve ion exchange, acid–base chemistry, solvent exchange, and sorption of neutral molecules from the gas phase. The insulating hosts have a fixed concentration of ionic guests that remains unchanged throughout subsequent reactions. The conducting host lattices have the feature that the concentration of ionic guest species can be altered by oxidation or reduction of the host. The chemistry of most compounds involves reduction and cation intercalation with the major exceptions of graphite and some layered oxides, which can be both reductively intercalated with cations and oxidized with anion insertion.The present understanding of the mechanism of intercalation with particular emphasis on layered structures is reviewed. Reactions involve adsorption of guest species on host crystals, exchange or insertion at the host surface, the formation of intermediate stages in layered compounds, and transport within the host lattice. Macroscopic effects such as variations in crystal size, dislocations, stacking faults, and pore mouth blockage can strongly influence the reaction kinetics.The major classes of host lattices in each category and their chemical behavior are described. The insulating materials discussed include zeolites, clays, layered double hydroxides, acid phosphates, and layered oxides while graphite, C60, carbon nanotubes, transition metal chalcogenides, metal phosphorus trisulfides, metal oxyhalides, metal nitride halides, and metal oxides are the major examples of conducting hosts. In the case of metal oxides, examples of both reductive intercalation of lithium ions and oxidative intercalation of oxide ions are discussed. These two types of intercalation reactions are important for lithium batteries and high‐temperature superconductivity, respectively.
Iridium: Organometallic Chemistry
Authors: Merola Joseph S. 
Published: December 2011

AbstractThe organometallic chemistry of iridium is reviewed. The general classes of complexes of iridium containing iridium to carbon bonds are surveyed. The preparations of iridium olefin complexes, iridium arene complexes, iridium carbonyl complexes, iridium cyclopentadienyl complexes, and other types of complexes are covered along with the use of those classes of compounds in preparing other organometallic iridium species. In addition, three areas in which organoiridium compounds find particular application are specifically reviewed: catalysis utilizing organometallic compounds of iridium, carbon–hydrogen (CH) bond activation chemistry with iridium, and hydrodesulfurization (HDS) studies using iridium. References to other reviews, to monographs, and to the primary literature are provided in all cases.
Iron: Heme Proteins, Mono‐ & DioxygenasesBased in part on the article Iron: Heme Proteins, Mono‐ & Dioxygenases by Masanori Sono & John H. Dawson which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Wong Luet‐Lok , Bell Stephen G. 
Published: December 2011

AbstractHeme (iron protoporphyrin IX) proteins and enzymes play crucial roles in all living organisms. Iron is very tightly bound to the porphyrin and does not dissociate under physiological conditions. Indeed the heme group is almost like a separate element altogether. It is redox‐active, and heme proteins such as cytochromechave important electron‐transfer functions. The strong π donor nature of heme iron(II) also means that heme proteins are involved in the binding and activation of small molecules such as oxygen. The P450 heme monooxygenases use two electrons and two protons to activate O2, giving one molecule of water and a high‐valent iron‐oxo intermediate that is sufficiently reactive to attack aliphatic CH bonds in a diverse range of organic molecules. The heme dioxygenases, as the name implies, insert both oxygen atoms of the O2molecule into the substrate. The known heme dioxygenases are indoleamine ring cleavage enzymes but have not been studied in detail, and no crystal structure of the enzymes is available. It is known that the active form of the enzyme has Fe(II), and that both oxygen and superoxide could be the source of the two oxygen atoms inserted into substrates. The main focus of this article is on the cytochrome P450 monooxygenases.The P450 (CYP) superfamily of enzymes is found in virtually all organisms where they catalyze the oxidation of endogenous and exogenous organic compounds. These reactions are vital steps in the biosynthesis of steroids and other hormones, and the detoxification and oxidative removal of xenobiotics. The primary activity of P450 enzymes is CH bond oxidation, but other activities such as alkene epoxidation, CC bond cleavage, heteroatom oxidation, and even reductive reactions are known. These reactions and their mechanisms are surveyed. The major sections review and summarize the steps in the P450 catalytic cycle, the nature of the rate‐limiting step, the chemical properties and electronic structure of the heme in the intermediates, and the mechanism of CH bond oxidation. The unique activity of P450 enzymes does not arise solely from the heme group; the pivotal roles of the protein environment and dynamics are discussed. The mechanism of aliphatic CH bond oxidation is one of the great challenges in chemistry. The nature of the active intermediate in P450 catalysis and the mechanism of action remain controversial. The results of mechanistic and theoretical approaches are brought together and reviewed.
Iron: Heme Proteins, Peroxidases, Catalases & Catalase‐PeroxidasesBased in part on the article Iron: Heme Proteins, Peroxidases, & Catalases by Ann M. English which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Bhaskar B. , Lad Latesh , Poulos Thomas L. 
Published: December 2011

AbstractThis article describes recent advances made in understanding structure–function relationships in representative peroxidases, catalases, and catalase‐peroxidases. Emphasis will be placed on those enzymes for which crystal structures are available. Of particular interest are recent advances in elucidating the structure of peroxidase compounds I and II, important intermediates that are formed from the reaction of the enzyme with peroxides. The repertoire of known structures in the catalase/peroxidase superfamily now include KatG catalases‐peroxidases and di‐heme peroxidases. These new structures coupled with a wealth of biochemical and biophysical data have provided important new insights into structure and function.
Iron Proteins with Dinuclear Active Sites
Authors: Kurtz Donald M. 
Published: December 2011

AbstractIron proteins with dinuclear active sites include those containing stable nonheme, non‐sulfur diiron sites. Though still dwarfed by the numbers of heme or iron‐sulfur proteins, the list of proteins known to contain nonheme, non‐sulfur diiron sites has steadily expanded over the past thirty years. These proteins share the following active site properties: (1) two iron atoms separated by 4 Å or less; (2) stable high spin ferrous and ferric oxidation states; (3) terminal histidinyl imidazole, carboxylate and solvent ligands; (4) at least one ligand that bridges the two irons; and (5) magnetic superexchange coupling of the unpaired spins on the two irons mediated by the bridging ligand atom(s). With one possible exception, the bridging ligands are either known or are strongly suspected to include one or two carboxylates. Two distinct subclasses, the purple acid phosphatases and the flavo‐diiron enzymes, seem to have no structural or functional relationships to each other or to any of the other diiron enzymes. The oxygen‐carrying protein, hemerythrin, for many years served as the prototype for nonheme, non‐sulfur diiron proteins. However, its structure and function have turned out to be distinct from those of the O2‐activating enzymes, which now form the largest subclass of these diiron‐containing proteins, with at least seven distinct types known; the most numerous of these are the alkane (including methane) monooxygenases and fatty acyl desaturases. Evidence for catalytically competent high‐valent diiron intermediates resulting from reaction of the diferrous sites with dioxygen have been obtained for at least two of the O2‐activating enzymes. Among the most intriguing and mysterious of the O2‐activating enzymes are the membrane‐bound ‘eight‐His’ diiron desaturases and monooxygenases.
Iron Proteins with Mononuclear Active Sites
Authors: Emerson Joseph P. , Mehn Mark P. , Que Lawrence 
Published: December 2011

AbstractMetalloenzymes containing a mononuclear nonheme iron center are often involved in dioxygen metabolism. We have divided this superfamily of enzymes into seven subcategories: iron superoxide dismutase and superoxide reductase, lipoxygenase, catechol dioxygenases, α‐keto acid‐dependent enzymes, isopenicillinNsynthase, pterin‐dependent hydroxylases, and Rieske dioxygenases. The degree of catalytic versatility and coordination flexibility encompassed by these enzymes is unsurpassed by any other known metalloenzyme superfamily. Herein we discuss the present state of knowledge regarding their active site structures and the critical role the metal center plays in their respective catalytic mechanisms.
Lead: Inorganic ChemistryBased in part on the article Lead: Inorganic Chemistry by Philip G. Harrison which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Bharara Mohan S. , Atwood David A. 
Published: December 2011

AbstractThis article covers basic chemistry of lead(II) including coordination geometries of halides, pseudohalides, oxides, carboxylates, thiolates, and nitrogen and/or phosphorus‐containing ligands. Coordination number around lead(II) ranges from 1 to 12 but is by no means comprehensive. Tetrahedral four‐coordination is observed only for lead(IV) compounds with bulky ligands. Lead forms halide complexes with both oxidation states but lead(IV) halides are much less stable then monomeric lead(II) halides. Like lead(II) halides, lead pseudohalides also form complexes with donor molecules and these complexes are irregular with high coordination number. Binary and ternary oxides of lead have found importance in electronic and technological applications, while polymeric lead(II) alkoxides [Pb(OR2)] are insoluble and poorly characterized. Ternary and mixed oxides of lead with perovskite structure are electroactive and are characterized by large dielectric constants. Lead(II) chalcogenides especially PbS, are photoconductors and widely used in photoelectric cells and IR detectors. Lead derivatives of oxyacids and organic acid, containing bivalent lead are extensively used in organic synthesis as oxidizing agents. The variable structure of highly coordinate lead(II) carboxylates and their complexes are characterized by intermolecular association.207Pb NMR and potentiometry have been widely employed for study of lead compounds in solution. Reduction of lead in liquid ammonia or direct fusion of various metals at 700°C results in the formation of anionic clusters. Such species have been identified with207Pb NMR in solution or recently by laser ablation in gaseous state.
Magnetism of Extended Arrays in Inorganic Solids
Authors: Landee Christopher P. , Turnbull Mark M. 
Published: December 2011

Abstract
The dominant magnetic interaction in insulators is magnetic exchange. This quantum mechanical effect arises from the overlap of wavefunctions of two different paramagnetic centers, either directly (direct exchange) or through an intervening ligand (superexchange). The associated exchange energy is electrostatic in origin but formally equivalent to the difference between the single and triplet states for the two interacting electrons. Magnetic exchange, plus other effects arising from the orientation of an electronic moment to the lattice through spin‐orbit coupling, leads to a wide variety of magnetic behavior, as illustrated with examples of magnetically one‐dimensional lattices.
Manganese: Organometallic Chemistry
Authors: Sweigart Dwight A. , Reingold Jeffrey A. 
Published: December 2011

Abstract

Ever since the characterization of Mn
2
(CO)
10
in 1954, manganese has played an important role in the development of organometallic chemistry. In some ways, however, manganese has not been as prominently utilized in synthesis and catalysis as some other transition metals such as iron, cobalt, chromium, and so on. The low cost of the metal, its accessible oxidation states, and the versatility of its many reaction pathways suggest that manganese will play a feature role in the organometallic chemistry of the future. Herein, new developments in organomanganese chemistry are described. There have been significant advances in insertion reactions, nucleophilic additions to coordinated arenes, and the chemistry of manganese‐coordinated carbenes, vinylidenes, and cymantrenes. Of special interest are the recent demonstration of manganese‐mediated activation of strong covalent bonds in sulfur and nitrogen heterocycles and the construction of organomanganese coordination networks via self‐assembly of modular quinonoid complexes.
Mixed Valence Compounds
Authors: Fackler John P. 
Published: December 2011

AbstractThe concept of mixed valence has referred to compounds in which a given element exists for an appropriate time in what can be described as more that one formal oxidation number. Clearly it is a formalism that has limited meaning when electron delocalization occurs on a timescale at or near the frequency of vibrations. The formalism that historically has been valuable, the Robin and Day classification, classifies such substances into three types depending upon an ability of experiment to identify well defined oxidation states. When electron transfer occurs readily between these mixed valence species, the concept of mixed valence may lose its meaning. These types of compounds are of considerable interest today since the nature of the bonding connecting the components influences significantly the electronic properties of the material. Understanding these factors is needed to help us develop and understand organic and ionic high‐Tcsuperconductors.
Molecular Orbital Theory
Authors: Czech Paul T. 
Published: December 2011

AbstractThis entry outlines the development of theoretical chemistry from its origins to the present highlighting important several theories, techniques, and applications to inorganic chemistry. The field has evolved from the series of postulates that provide the framework for quantum mechanics and which culminated in the Schrödinger equation proposed in 1926. Soon thereafter, the application to chemical systems began. Valence Bond Theory (VBT) and Molecular Orbital (MO) Theory were initial techniques for explaining what for chemists was of critical importance, that is, the nature of the chemical bond in molecules. Each approach is still useful today. Molecular Orbital Theory, however, has enjoyed wider applicability owing to being much more easily handled quantitatively. The explosive growth of digital computing capabilities over the last half‐century can no doubt be traced in part to the intensive number crunching requirements of this type. The article reviews the early work of VBT and MO theory, and the treatment of H2, homonuclear, and heteronuclear diatomic molecules in some detail. Sections concerning the important application of mathematical group theory conventions and several techniques that use the self‐consistent field approach define much of the terminology that is commonly used in the field. An up‐to‐date list of references and related articles provided interested readers with much more detail on the techniques and applications in this enormous field.
Mössbauer Spectroscopy
Authors: Schünemann Volker , Paulsen Hauke 
Published: December 2011

AbstractMössbauer spectroscopy offers information about the structural, electronic, and dynamic properties of Mössbauer‐active isotopes. Within this contribution we will limit ourselves to57Fe Mössbauer spectroscopy and discuss how electronic and structural information of iron centers in inorganic and bioinorganic compounds as well as iron proteins can be obtained. An introduction to the basic principles and necessary sample requirements is followed by examples of Mössbauer spectroscopic work on metallic iron, iron nanoparticles, and thin films. The main part of this contribution contains an overview of selected examples of iron compounds in almost all oxidation states known so far, ranging from zero‐valent iron carbonyls to very recently reported ultra‐high‐valent Fe(VI) coordination compounds. In addition, a short overview on the theoretical calculation of Mössbauer parameters like isomer shift and quadrupole splitting by means of density functional theory is given. These calculations have been improved considerably in recent years and are expected to be used by an increasing number of inorganic chemists for the interpretation of spectroscopic results.
Nickel Enzymes & Cofactors
Authors: Ragsdale Stephen W. 
Published: December 2011

Abstract

This review covers the structure and function of the eight known Ni enzymes, with a focus on the chemistry and biology of the metallocenter. For the Ni redox enzymes, the Ni ion exhibits versatility in redox properties in exploiting the +3/+2 (superoxide dismutase and hydrogenase), the +2/+1 (hydrogenase, CO dehydrogenase, acetyl‐CoA synthase, and methyl‐CoM reductase), and perhaps even reaching the 0 (acetyl‐CoA synthase) states for the redox enzymes. On the other hand, the nonredox Ni enzymes (urease, glyoxylase‐I, aci‐reductone dioxygenase) apparently remain in the +2 state during catalysis. The Ni site(s) in these enzymes adopt a wide variety of coordination environments; some form mononuclear square planar or octahedral complexes, while others are homo‐ or hetero‐ (with iron) dinuclear with oxo or thiolato bridges and still others join heteromultinuclear clusters. Acetyl‐CoA synthase contains the most complex Ni metallocenter yet described, which is a [4Fe–4S]
2+
cluster bridged by a cysteine thiolate to a binuclear NiNi center. The three‐dimensional structures of all these enzymes are known and some (acetyl‐CoA synthase, aci‐reductone dioxygenase, CO dehydrogenase, and superoxide dismutase) have been determined in the past two years leading to a significant reinterpretation of spectroscopic results. In many Ni enzymes, density functional theory has begun to play a major role in assigning active‐site structures and testing mechanistic hypotheses.
Nickel: Inorganic & Coordination Chemistry
Authors: Collinson Simon R. , Schröder Martin 
Published: December 2011

AbstractThe general features and coordination chemistry of Ni0to NiIVand complexation to cyanide, N‐, P‐, O‐, S‐, and halide‐donor ligands are detailed. The reactivity of NiIIcomplexes in the template synthesis of macrocycles and for the oligomerization and polymerization of alkenes are highlighted. The stabilization of radical NiIand NiIIIcenters is related to the associated ligand types and metal‐ion stereochemistries. The supramolecular chemistry of NiIIincludes the formation of aggregates, framework polymers, and receptors. The structures of a number of Ni‐containing enzymes have been elucidated and the formation of low‐molecular weight complex mimics is discussed.
Niobium & Tantalum: Organometallic ChemistryBased in part on the article Niobium & Tantalum: Organometallic Chemistry by David E. Wigley which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Wang Ruitao , Xue Ziling 
Published: December 2011

AbstractThis review highlights leading literature in syntheses, characterization, structures, and reactivities of organometallic complexes of niobium and tantalum between 1993 and early 2003. Such complexes include monometallic and bimetallic species. The applications of niobium and tantalum organometallic complexes in catalysis and metal‐mediated organic synthesis are discussed as well.
Nitrides: Transition Metal Solid‐State ChemistryBased in part on the article Nitrides: Transition Metal Solid State Chemistry by Peter Ettmayer & Walter Lengauer which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Lengauer Walter , Eder Alexander 
Published: December 2011

Abstract

Basic properties and properties interesting for applications of transition metal nitrides are presented in this article. Starting from crystal chemistry, bonding, and preparation, the article also briefly discusses analytical chemistry of chemical and physical nitrogen analysis and standardization as well as thermodynamics. Updated portions of phase diagrams of group 4–6 transition metals with nitrogen are presented. A substantial part is devoted to the solid‐state properties because they make nitrides interesting for application. The presentation of these properties includes hardness, thermal expansion, nitrogen diffusivity, thermal properties, electrical conductivities, superconductivities, and elastic properties. Several of these properties are given as a function of temperature and composition. The topic is closely connected to article (
see
Carbides: Transition Metal Solid‐state Chemistry).