bluuebunny/crossref_metadata_2025 huggingface dataset:
Boron: Organoboranes
Authors: Jäkle Frieder
Published: December 2011

This chapter provides an overview of recent developments in the highly interdisciplinary field of organoboron chemistry. The most important routes for the synthesis of organoboranes via transmetallation, hydroboration and other boration reactions, as well as CH activation are outlined. The various classes of organoboranes thus accessible are presented according to the nature of the organic substituents. Special emphasis is given to applications of organoboranes. For example, the development of new chiral organoboranes that are commonly used in enantioselective synthesis is shown. Moreover, the importance of fluorinated arylboranes as highly efficient Lewis acid catalysts and cocatalysts for organic transformations and polymerization reactions is discussed. The use of triarylboranes and related compounds as electronic and optical materials for device applications, and as sensors for the recognition of anions and neutral Lewis bases is also described in detail.
Boron: Polyhedral CarboranesBased in part on the article Boron: Polyhedral Carboranes by Robert E. Williams which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Hosmane Narayan S. , Maguire John A.
Published: December 2011

Carboranes are compounds in which carbon, boron, and hydrogen atoms are present in polyhedral cages. The cages are stabilized by multi‐centered bonds, which gives the carboranes unique chemical and structural properties. Many of these compounds are chemically and thermally stable enough to allow their use as boron delivery agent for boron neutron capture therapy (BNCT) in cancer treatment and as molecular assemblies.
Carbon: Inorganic ChemistryBased in part on the article Carbon: Inorganic Chemistry by R. Bruce King which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Friščić Tomislav , MacGillivray Leonard R.
Published: December 2011

The article provides a brief and general overview of the chemical and physical properties of carbon, as it relates to inorganic chemistry. Several allotropic forms of carbon are described, with general properties discussed. The characteristics and synthetic methods for the preparation of simple compounds involving carbon or carbon and hydrogen with halogens, oxygen, sulfur, as well as nitrogen, are provided. In addition, recent developments in supramolecular chemistry to construct ladder‐like carbon frameworks are outlined.
Carbonylation Processes by Homogeneous CatalysisBased in part on the article Carbonylation Processes by Homogeneous Catalysis by George G. Stanley which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Parr M. L.
Published: December 2011

This article reviews homogeneously catalyzed carbonylation reactions with particular emphasis on catalytic hydroformylation using cobalt, rhodium, platinum, and palladium complexes. The carbonylation of methanol based on rhodium and iridium complexes (Monsanto and Cativa
™
processes, respectively) is also discussed. Examples of the utility of carbonylation in the synthesis of complex molecules are given.
Cobalt:B12Enzymes & Coenzymes
Authors: Kräutler Bernhard
Published: December 2011

The most prominent biological role associated with cobalt concerns vitamin B12, its natural variants, and its coenzyme forms. The B12‐derivatives are cobalt complexes of the unique and remarkably complex corrin ligand that belong to the larger class of the tetrapyrrolic natural compounds. The ‘antipernicious anemia factor’ vitamin B12and its cofactor forms are, first of all, required for human and animal health. However, except for the higher plants, all forms of life appear to depend upon the natural variants of vitamin B12. The main chemical reactivities of the corrinoids (needed to fulfill their essential biological roles) may reflect their possible corresponding chemical contributions to the development of the early stages of life on earth. Indeed, the corrinoids play a particularly basic role in carbon metabolism in microorganisms, which also are the only natural sources of the B12‐derivatives. Microorganisms have developed extraordinary means for the biosynthesis, and for the regulation of the biosynthesis of the B12‐derivatives, in order to cope with the structural and functional complexity of these tetrapyrrolic cobalt‐compounds, while most (other) forms of life have evolved intricate strategies for the economic and efficient uptake and transport of the corrinoids. The known cofactor functions of the cobalt‐corrinoids are due to their extraordinary organometallic chemistry and their redox chemistry under physiological conditions: Coenzyme B12, methylcorrinoids, and reduced corrinoids are the cofactors in various important and unique organometallic enzymes, whose intricate structural and mechanistic properties are the current focus of strong and broad research activities. The essential role of the corrinoids in the remarkable organometallic paths of carbon fixation and further carbon metabolism in anaerobic microorganisms has attracted particular attention. Vitamin B12and its derivatives thus hold an important position in all of the life sciences and are at the center of particular interdisciplinary interest from such diverse areas as medicine, biology, chemistry, and physics.
Coordination & Organometallic Chemistry: Principles
Authors: Crabtree Robert H.
Published: December 2011

The title topic is reviewed. Under coordination chemistry, special attention is given to Werner complexes, the trans effect, soft and hard ligands, crystal and ligand field (LF) models, together with oxidation state and coordination number. Under organometallic chemistry, the main topics include electroneutrality, back bonding, the 18‐electron rule, and effects of complexation.
Copper Proteins with Dinuclear Active SitesBased in part on the article Copper Proteins with Dinuclear Active Sites by Konrad Lerch which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Decker Heinz
Published: December 2011

Copper proteins with dinuclear active sites comprise proteins with different structures and functions. The phenoloxidase, tyrosinase, and catecholoxidase are responsible for browning by starting the synthesis of melanin. These enzymes are involved in the primary immune response in invertebrates, plants, fungi as well as in the sclerotization of arthropods. The respiratory proteins hemocyanins are responsible for oxygen transport in some arthropods and molluscs. However, they can be converted to enzymes exhibiting phenoloxidase activity. Based on X‐ray structures of hemocyanins and a catecholoxidase, large parts of folding motifs are very similar although the sequence identities are far below 30%. A model for the activation process of phenoloxidase activity is presented.
Copper Proteins with Type 1 SitesBased in part on the article Copper Proteins with Type 1 Sites by Edward N. Baker which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Hart P. John , Nersissian Aram. M. , George Serena DeBeer
Published: December 2011

Copper Proteins with Type 1Sites is a general review that focuses on single‐domain proteins that bind ‘blue’ or ‘type 1’ copper. Larger, multidomain proteins that contain type 1 copper in addition to other types of copper centers are not discussed at any length in this article. Blue copper proteins are so named because in solution they are a brilliant blue/azure color when the copper ion is in its Cu(II) oxidation state. The bright blue color comes from a charge transfer (CT) between Cu(II) and the sulfur (thiolate) of a ligating cysteine residue. Because of this intense color, type 1 copper proteins were among the first to be isolated because they could be tracked easily during purification processes. This, together with their unique spectroscopic properties that have no parallel in small‐molecule copper complexes, has made them the subject of intense study over the last 35 years. This article focuses on three main aspects of type 1 copper proteins: (1) their occurrence, distribution, and classification based on analyses of genomic and expressed sequence tag data; (2) their three‐dimensional structures as determined by the well‐established tools of single‐crystal X‐ray diffraction and nuclear magnetic resonance (NMR); and (3) their electronic, spectroscopic, and electron‐transfer properties.
Dinuclear Organometallic Cluster Complexes
Authors: Kiss Gabor , McDonough James Eric , Weir John J. , Hoff Carl D.
Published: December 2011

Metal–metal bonding in dinuclear complexes plays a key role in inorganic and organometallic chemistry. It is the basis for development of polymers and clusters derived from this simple unit. Its chemistry now approaches the ‘functional group’ status, typically used in organic chemistry for classes of compounds. However, owing to the array of metals and oxidation states involved, a wide range of structures, reactions, and properties are observed for this important class of compounds. This article introduces the topic of metal–metal bonded complexes and attempts to outline the synthetic strategies used to prepare metal–metal bonded complexes, some of their characteristic properties and reactions, as well as to provide a brief introduction to historical development and emerging directions of this central area of inorganic chemistry.
Electron Transfer Reactions: TheoryBased in part on the article Electron Transfer Reactions: Theory by Roderick D. Cannon which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Matyushov Dmitry
Published: December 2011

This article discusses the progress in the field of electron‐transfer theory over the period of about 50 years since early 50s marked by the development of theories of radiationless transitions in molecules in the gas phase and the Marcus theory of electronic transitions between ions in solution. The article starts with the classification of electron‐transfer reactions in terms of reaction mechanisms and the extent of electronic delocalization. This is followed by the outline of the picture of intersecting parabolas due to Marcus, which defines the activation barrier for nonadiabatic electron transfer. The rate of nonadiabatic electron transfer strongly depends on electronic coupling between the donor and acceptor states. The Mulliken‐Hush theory, along with its recent generalizations, provides coupling from spectroscopic observables. The success of electron‐transfer theories has largely been supported by the connection between thermal rates and optical spectroscopy. The activation barrier can be obtained from optical spectra by using the band‐shape analysis discussed next. This is followed by the overview of the inverted region of electron transfer and the consequences of introducing nonparabolic free energy surfaces of electron transfer in polarizable systems. The advent of ultrafast spectroscopic techniques opened up a new avenue in electron‐transfer research related to the effects of polarization dynamics on the reaction rate. Measurements at varying pressure allow one to introduce an additional thermodynamic variable probing the activation barrier. The article concludes with a brief account of magnetic effects in electron transfer.
Electronic Structure of Clusters
Authors: Wales David J.
Published: December 2011

The electronic structure of main group and transition metal clusters is reviewed in the context of electron‐counting rules. A consistent framework for rationalising and extending these rules is presented in terms of Stone's tensor surface harmonic theory. Several applications are described to show how the theory works, along with predictions for cluster rearrangement mechanisms.
Electronic Structure of Main‐Group CompoundsBased in part on the article Electronic Structure of Main Group Compounds by Jeremy K. Burdett which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Frenking Gernot , Lein Matthias
Published: December 2011

Quantum chemical research has made significant progress in the understanding of the electronic structure and the nature of the interatomic interactions yielding chemical bonds in molecules. Ad hoc models of chemical bonding have been complemented or replaced by more sophisticated approaches for analyzing the bonding situation in molecules. The new methods build a well‐defined bridge between the heuristic bonding models using pictorial approaches and the physical mechanism of a chemical bond. Bonding models can be examined with quantum chemical methods, which show that chemical intuition and physics do not exclude each other. The paper describes important methods using charge and energy partitioning approaches, which are helpful and widely used in modern theoretical inorganic chemistry for understanding the electronic structure and bonding situation of main‐group compounds. The application of the methods to representative main‐group compounds is described and the results are critically discussed.
Electronic Structure of Organometallic Compounds
Authors: Albright Thomas A.
Published: December 2011

A brief treatment of the concept of orbital interaction is given, particularly in reference to the transition metal‐ligand bond. This is then applied to the σ splitting pattern for the ML

n

series where
n
 = 6, 5, 4 (square planar and tetrahedral), 3, and 2 cases. Here M is a transition metal and L is a generic ligand with a σ donor function. A description is given for how the splitting pattern is modified when one or more of the ligands have π acceptor or donor functions. Several examples illustrate how symmetry can sometimes create modification to the normal electron counting rules. A detailed discussion is given of how to create the important valence orbitals of an ML

n

fragment and several examples are given of their use to build up the orbitals of large organometallic molecules. Finally, a detailed discussion is given of the construction and use of the isolobal analogy.
Gallium: Inorganic ChemistryBased in part on the article Gallium: Inorganic Chemistry by Andrew R. Barron which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Banger Kulbinder Kumar , Hepp Aloysius F.
Published: December 2011

An overview of the inorganic chemistry of gallium and its compounds is reported in detail with an attempt to bring up to date current studies in this field. In addition, the use of various Ga related alloys as either binary or ternary semiconducting material for bulk, thin film, and nanotechnology is reported in detail pertaining to their synthesis, properties, and application. The chemistry of Ga inorganic and coordination derivatives is also reviewed and discussed.
Gallium: Organometallic ChemistryBased in part on the article Gallium: Organometallic Chemistry by Andrew R. Barron which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Robinson Gregory H.
Published: December 2011

The organometallic chemistry of gallium has experienced substantial growth over the past decade. Much of this work concerned the development of the organometallic chemistry of compounds containing GaGa bonds. This would include simple dimeric compounds, gallium ring compounds, and small gallium clusters. This chapter will discuss the synthesis and structural aspects of these compounds.
Germanium: Organometallic Chemistry
Authors: Banaszak Holl Mark , Peck David R.
Published: December 2011

This article provides an overview of the organometallic chemistry from 1994 to 2004. Major advances in the formation and breaking of GeC bonds are discussed, as are advances in the physical characterization of these compounds. Recent advances in the formation of organogermanium species containing multiple bonds to germanium and the formation of germanium‐centered radicals and cations are delineated. Applications to the synthesis of germanium‐containing polymers are overviewed.
Gold: Inorganic & Coordination Chemistry
Authors: Vittal Jagadese J. , Puddephatt Richard J.
Published: December 2011

Gold compounds are finding new applications in catalysis, medicine, and molecular materials, based on their reactivity and unusual physical and chemical properties. The theoretical basis of the unique properties of gold compounds continues to develop rapidly and provides a constant challenge for synthesis of new types of gold compounds. This chapter gives an overview of these exciting developments while giving an overview of the modern inorganic chemistry of gold.
Hydroboration CatalysisBased in part on the article Hydroboration Catalysis by Kevin Burgess & Wilfred A. van der Donk which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Vogels Christopher M. , Westcott Stephen A.
Published: December 2011

Among the most significant advances in organic synthesis over the past few decades are those associated with the development of transition metal complexes for their use as catalysts in organic reactions. The discovery that transition metals can also be used to catalyze the addition of BH bonds to unsaturated substrates has provided the synthetic chemist with another valuable tool. This review examines recent advances in the field of catalyzed hydroborations and their applications in organic synthesis.
Hydrogenation & Isomerization of Alkenes
Authors: Jardine Fred H.
Published: December 2011

Alkenes are isomerized by complexes of late, second or third series transition metals. This occurs either by successive β‐hydride abstraction reactions or, more rarely, by a π–allylic mechanism. Both decyclization and annulation reactions of strained, cyclic hydrocarbons are catalyzed by these complexes. Palladium complexes are active catalysts for the Cope‐ and Claisen rearrangements. Homogeneous, catalytic hydrogenation can occur via three possible routes. Ruthenium complexes catalyze transfer hydrogenation. Catalyst modifications can be made to minimize by‐product formation during hydrogenation or deuteriation.
Indium: Organometallic Chemistry
Authors: Kumar Banger Kulbinder
Published: December 2011

An overview of the chemistry of organoindium compounds containing at least one InC bond over the last ten years is reported in detail. In particular, the synthesis, characterization, properties of homoleptic and heteroleptic organoindium derivatives, organoindium(0), (I), and (II) compounds, and in addition anionic compounds are also reported. Furthermore, the use of organoindium compounds for thin film, nanotechnology, and organic synthesis is discussed.
Cluster Compounds: Inorganometallic Compounds Containing Transition Metal & Main Group Elements
Authors: Fehlner Thomas P.
Published: December 2011

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

The 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

The 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

Heme (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

This 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

Iron 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

Metalloenzymes 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

This 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.
Macrocyclic Ligands
Authors: Bowman‐James Kristin
Published: December 2011

The main classes of macrocyclic ligands are classified. Emphasis is placed on O and N donors but S, P and As‐donors are also included. The macrocyclic effect and anion coordination are both discussed.
Magnetism of Extended Arrays in Inorganic Solids
Authors: Landee Christopher P. , Turnbull Mark M.
Published: December 2011

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.
Magnetism of Transition Metal Ions
Authors: Hatfield William E.
Published: December 2011

The title topic is discussed with emphasis on the interpretation of experimental data. Typical examples are also discussed.
Manganese: Organometallic Chemistry
Authors: Sweigart Dwight A. , Reingold Jeffrey A.
Published: December 2011

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

The 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

This 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

Mössbauer 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

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

The 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

This 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

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).
Noble Gases: Inorganic ChemistryBased in part on the article Noble Gases: Inorganic Chemistry by Boris Žemva which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Atwood David A.
Published: December 2011

The noble gas (Ng) elements have a rich reaction chemistry despite having a filled valence shell that would indicate otherwise. Halide compounds, usually with fluorine, and various oxides are common. There is also a growing class of carbon and nitrogen derivatives. A wide range of neutral and cationic noble gas compounds can be formed as long as the added elements, or combinations of elements, possess sufficient electron affinity. The range of compounds, along with characterization data and brief bonding descriptions will be presented for each element. Many of the compounds serve as starting materials for other derivatives, including the rapidly growing field of noble gas containing transition metal complexes. For example, there is now a broad range of salts containing transition metals. The article will conclude with a brief overview of the many unusual and disparate applications being found for these elements.
Noncrystalline Solids
Authors: Adam Jean‐Luc , Lucas Jacques
Published: December 2011

This review deals with the formation and physical properties of noncrystalline materials in oxide and nonoxide systems. Structural aspects are also developed. Oxide materials are silica‐based glasses, borate, and phosphate glasses, while nonoxide systems include halide and chalcogenide glasses. They are described in terms of chemical compositions and thermal and optical properties. Special attention is paid to the unique properties of nonoxide glasses for infrared‐light transmission and rare earth emissions. Some applications in the fields of infrared optics, infrared fiber sensors, fiber lasers, and amplifiers are shown. In a special section, the formation and properties of metallic glasses are presented, with special focus on chemical, magnetic, and mechanical properties.
Nutritional Aspects of Metals & Trace ElementsBased in part on the article Nutritional Aspects of Metals & Trace Elements by Paul Saltman which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Yokoi Katsuhiko
Published: December 2011

The essential inorganic nutrients are dietary components that exert nutritional function when they are consumed as inorganic substances. Some essential inorganic nutrients such as selenium and iodine act as organic active constituents after metabolic conversionin vivowhen they are consumed as organic as well as inorganic substances. Inadequate intake of essential inorganic nutrients results in deficiency diseases and/or interruption of life cycles. The essential inorganic nutrients consist of the major elements (sodium, potassium, calcium, magnesium, chlorine, phosphorus, and sulfur) and the trace elements (iron, copper, zinc, manganese, cobalt, chromium, molybdenum, vanadium, nickel, arsenic, selenium, iodine, fluorine, silicon, boron, tin, cadmium, lead, rubidium, and lithium). Evidence of essentiality is limited for arsenic, boron, cadmium, fluorine, lead, lithium, nickel, rubidium, silicon, tin, and vanadium. If the requirement is less than 1 mg day−1for humans or 1 mg kg−1diet for animals, the inorganic nutrients are called ultratrace elements. Further investigation may increase the number of essential inorganic nutrients. Deficiencies of inorganic nutrients such as iodine, iron, and zinc occur worldwide. To prevent deficiencies and toxicosis, the US and other nations have established the Dietary Reference Intakes (DRIs) or the equivalents that are composed of reference values including Estimated Average Requirements (EARs), Recommended Dietary Allowances (RDAs), Adequate Intakes (AIs) and Tolerable Upper Intake Levels (ULs). Essential inorganic nutrients function in vivo through various modalities such as catalytic centers of enzymes, metabolic regulation, modulation of ion channels and receptors. The regulation and control of inorganic nutrients are a function of eight parameters: availability, solubility, permeability, ligand exchange, transport, assimilation, storage, and excretion. Excessive intakes, genetic abnormalities, and other etiologies cause pathologies of metal overload. Functions of selenium and nickel were reviewed. Selenium manifests antioxidant activity as an active site of glutathione peroxidase. Other important selenium‐containing proteins include thioredoxin reductase, iodothyronine deiodinases, selenoprotein P. Nickel occupies the metal centers of urease, carbon monoxide dehydrogenase, and other enzymes. Nickel deprivation results in impaired reproduction (rats and goats) and decreased spermatozoa motility and density (rats). It is our challenge to determine optimal intakes of inorganic nutrients for ensuring optimal health for all.
Organic Synthesis Using Transition Metal Complexes Containing π‐Bonded LigandsBased in part on the article Organic Synthesis using Transition Metal Complexes Containing π‐Bonded Ligands by Martin F. Semmelhack which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Morris W. H. , Sullivan Lisa M. , Wellons Matthew S. , Lukehart C. M.
Published: December 2011

A selective overview of reactions of transition metal π‐complexes pertaining to organic synthesis applications is provided. While reactions involving nucleophilic addition to pi‐coordinated ligands are emphasized, alkene insertion/elimination reactions and allyl coupling reactions are also discussed.