bluuebunny/crossref_metadata_2025_split huggingface dataset:
Indium: Inorganic ChemistryBased in part on the article Indium: Inorganic Chemistry by Dennis G. Tuck which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Zhao Yanbao , Zhang Zhijun 
Published: March 2006

Abstract

This review highlights the development in inorganic chemistry of indium made in the last ten years. The first parts of this article describe the preparation of new low‐valence indium complexes and organoindium (III) compounds, and the use of these compounds as starting materials for further synthesis. A special highlight is the compounds R
4
In
4
and R
4
In
2
, which show the lively development and the current trends in this field. The following parts present the development of organoindium compounds with group 15 or 16 ligands as single‐source molecular precursors for the deposition of indium‐containing semiconductors by MOCVD; the preparation and characterization of nanoparticles, nanowires, and nanotubes of indium metal, alloys, oxides, and indium‐V/VI semiconductors, which play a sizable role in the new generation of nanoscale electronic and optical devices; and the preparation of new indium intermetallic compounds, which present large structural variety and peculiar magnetic and electrical properties. The last part advances the applications of indium and indium halides in organic synthesis with particular reference to regio‐, stereo‐, and chemoselectivity. These reactions include the regioselective allylation of unsaturated functional groups, the acylation of alcohols and amines, the rearrangement of epoxides, the stereoselective debromination, and other reactions.
Cluster Compounds: Inorganometallic Compounds Containing Transition Metal & Main Group Elements
Authors: Fehlner Thomas P. 
Published: March 2006

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.
Iridium: Inorganic & Coordination Chemistry
Authors: Housecroft Catherine E. 
Published: March 2006

AbstractThis article provides an overview of the inorganic and coordination chemistry of iridium, beginning with a summary of physical properties, accessible oxidation states, and common coordination geometries. Solid‐state compounds are summarized with pertinent examples. Mononuclear compounds and complexes are classified according to the oxidation state of the iridium center and the donor atom(s) of the ligand; dinuclear and multinuclear complexes are discussed in a separate section. References make use of review articles where appropriate, as well as the primary literature. It is not the aim of this article to provide a comprehensive survey of the chemistry of iridium.
Iron: Heme Proteins, Mono‐ & DioxygenasesBased in part on the article Iron: Heme Proteins, Mono‐ & Dioxygenases by Masanori Sono & John H. Dawson which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Wong Luet‐Lok , Bell Stephen G. 
Published: March 2006

Abstract

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 cytochrome
c
have 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 O
2
, 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 O
2
molecule 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: March 2006

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: Models of Proteins with Dinuclear Active SitesBased in part on the article Iron: Models of Proteins with Dinuclear Active Sites by Will E. Lynch & Donald M. Kurtz, Jr. which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Chavez Ferman A. , Que Lawrence 
Published: March 2006

Abstract
The nonheme diiron enzymes are a class of metalloproteins that share a common function in the binding and activation of dioxygen. In recent years, interest in these enzymes has grown at a steady rate. The focus is both of a fundamental and applied nature. Understanding how these enzymes have evolved to perform synthetically challenging organic transformations under moderate conditions will provide insights into evolutionary processes and possibly help to develop techniques for engineering such active sites into proteins. These studies have led to the development of synthetic catalysts for these transformations through the ‘biomimetic’ approach. Through structural studies it has become clear that many of the metal binding sites in nonheme diiron enzymes possess carboxylate‐rich ligation, which is believed to be important in facilitating redox processes and structural rearrangements during catalysis. The use of model compounds to study these enzymes has many advantages that are not offered with other approaches. For example, a model for a proposed reactive intermediate may be stabilized at low temperature and studied. Synthetic compounds can also be selectively modified to examine the influence of a certain geometry, ligand set, or chemical environment on the properties and reactivity of the compound. In this article, several approaches are discussed toward the development of diiron model compounds. In one approach, multidentate ligands possessing two metal binding sites are examined. This approach has led to metal complexes with closely spaced iron centers, a key structural feature in these enzymes. In a second approach, mononuclear metal complexes supported by multidentate ligands are bridged by oxygen groups to generate the diiron core structure. A third approach focuses on dicarboxylate ligands that bridge the two iron centers. This approach allows for variation of the remaining terminal ligands. The fourth approach relies on steric interactions. Intramolecular ligand interactions are used to control the geometry of the diiron complex. To date, these four approaches have been very successful in generating many of the intermediates seen in the diiron enzyme catalytic cycles and a few have been shown to reproduce the catalytic activity to some extent. It is anticipated that many more insights will be garnered from model studies and that new chemistries will be discovered.
Iron–Sulfur Proteins
Authors: Johnson Michael K. , Smith Archer D. 
Published: March 2006

AbstractIron–sulfur proteins contain iron coordinated by at least one sulfur ligand and include proteins with mononuclear Fe centers with partial or complete cysteinyl sulfur ligation as well as proteins containing clusters of iron and inorganic sulfide. This review summarizes the structural, electronic, and redox properties of protein‐bound mononuclear FeS centers and FeS clusters containing [2Fe2S], [3Fe4S], and [4Fe4S] cores. In addition to the ubiquitous role in mediating biological electron transport, the roles of FeS centers have proliferated to include coupling of electron and proton transfer, substrate binding and activation, determining protein structure, regulation of gene expression and enzymatic activity, disulfide reduction, and iron, electron, or cluster storage. The diverse roles of FeS clusters are illustrated by discussion of specific systems: the mitochondrial and photosynthetic electron transport chains and a wide range of soluble redox enzymes and proteins; the active sites of nitrile hydratase, aconitase‐type (de)hydratases, superoxide reductase (SOR), radical‐SAM (S‐adenosylmethionine) enzymes, NiFe‐ and Fe‐hydrogenase, sulfite and nitrite reductase, nitrogenase, CO dehydrogenase, and acetyl‐CoA synthase; the structural FeS centers in DNA repair enzymes; the regulatory roles of FeS centers in the SoxR, fumarate–nitrate reduction (FNR), IscR/SufR, and iron‐regulatory protein (IRP) proteins and in selected enzymes; the two classes of FeS cluster containing disulfide reductases typified by ferredoxin–thioredoxin reductase (FTR) and heterodisulfide reductase (HDR); and the role of 8Fe ferredoxins and polyferredoxins in iron, electron, or cluster storage.
Iron Transport: Siderophores
Authors: Matzanke Berthold F. 
Published: March 2006

AbstractSiderophores (from the Greek: iron carrier) are low molecular mass (500–1500 Da) iron chelators that are synthesized in bacteria and fungi under conditions of iron deficiency. Siderophores exhibit extraordinarily high complex formation constants for ferric iron with β‐values ranging from 1020to approximately 1050. Fe2+‐siderophores are some 20 orders of magnitude less stable than their Fe3+counterparts. The d5 electronic configuration of Fe3+rules out any crystal field stabilization energy and makes ferric iron complexes relatively labile with respect to isomerization and ligand exchange. Siderophores display a selectivity for iron that is reflected in the corresponding complex stability constants that are higher with Fe3+than with Al3+, or with bivalent cations like Ca2+, Cu2+or Zn2+. Microorganisms excrete desferrisiderophores in order to scavenge iron from the environment. The competition for iron by siderophores, the mechanisms of siderophore uptake through microbial membranes, and the intracellular pathways of siderophore‐iron utilization strongly depend on thermodynamic, kinetic, and structural features of the ferric iron siderophore complexes.The structural features of siderophores are diverse. The ligating groups contain oxygen atoms of hydroxamate, catecholate, α‐hydroxy carboxylic and salicylic acids, or oxazoline and thiazoline nitrogen. Reduction potentials of ferric siderophore complexes vary between −700 and −150 mV. In particular at the low potential end below −450 mV, special biological strategies of reductive iron removal are required because these potentials are too negative for typical cellular reductases.The coordination and redox chemistry of siderophores is also reflected in the mechanisms of siderophore‐mediated iron uptake in microorganisms. A classic example is the intracellular removal of iron from enterobactin. The permeation of cell walls or bacterial membranes by siderophores is in most microbes a highly specific process requiring an array of up to eight proteins. The advent of modern molecular biology delivered a cornucopia of methods enabling high‐yield production of specific gene products relevant to siderophore synthesis and transport, analyses of structure‐function relationships (employing site directed mutagenesis), and detailed insights into the regulation of the corresponding processes.One siderophore, ferrioxamine B, serves as a detoxifier in iron overload diseases and in the treatment of β‐thalassemia. Siderophores and siderophore analogs also play a role in MRI and are employed as basic models for actinide chelators in order to remove these metals from the environment or from a contaminated body.
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: March 2006

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.
Ligand Field Theory & Spectra
Authors: Smith Derek W. 
Published: March 2006

AbstractIn any chemical environment – traditionally represented as a crystal field (CF), in which the donor atoms are represented by point charges – annd subshell loses its fivefold degeneracy. The consequent splitting is described in detail for cubic (octahedral and tetrahedral) systems. The pure CF approach has serious shortcomings, but the effects of covalency can be accommodated without losing its simplicity altogether; this is often calledligand field theory(LFT). CF/LFT is important in the interpretation of the d–d spectra of complexes; the d–d states arising from cubic dnsystems and their relative energies are analyzed, along with a discussion of the nephelauxetic effect. As examples of the analysis of d‐orbital splittings in noncubic complexes, chlorocuprates(II) and tetragonal tetraamminechromium(III) complexes are examined in detail, using the angular overlap and cellular ligand field models. Among applications of LFT, ligand field stabilization energy (LFSE) is useful in the rationalization of thermodynamic and kinetic observations. The Jahn–Teller effect is important in the structural chemistry of copper(II) especially.
Luminescence
Authors: Fouassier C. 
Published: March 2006

AbstractThis chapter is devoted to the luminescence of inorganic compounds. Luminescence characteristics are strongly host‐dependent. This is illustrated by various examples of the influence of covalency, crystal field, phonon energies, and structural features. The chapter is organized as follows.Section 2 describes the fundamentals of luminescence: probability of electronic transitions, shape of emission bands, quantum efficiency, energy transfer, and factors governing the position of the emitting level (nephelauxetic effect and crystal field splitting).Section 3 reviews the main families of luminescent ions: transition metal ions, lanthanide ions, and s2ions. The various types of electronic transitions responsible for the luminescence of transition and lanthanide ions are presented: nd → nd, (n + 1)s → nd, and charge transfer (CT) transitions for the former, 4f → 4f, 5d → 4f, and CT transitions for the latter. Data are given on the luminescence wavelength range, excited‐state lifetimes, thermal stability, and concentration quenching.Section 4 deals with donor‐acceptor transitions in ZnS.Section 5 presents the luminescence mechanisms for excitation through the host lattice. Vacuum ultraviolet (VUV), electron beam, X‐ray, and γ‐ray excitation are considered. The most efficient luminescent materials are given for the various types of excitation.Section 6 deals with electroluminescent materials.
Magnetic Oxides
Authors: Greedan John E. 
Published: March 2006

Abstract
An attempt has been made to survey the research activity in selected aspects of the field of magnetic oxides for the period ∼1993 to the present. Emphasis has been placed on oxides with the perovskite and related structures such as the Ruddlesden–Popper phases, A‐site and B‐site ordered perovskites, pillared perovskites, and materials with structures related to the hexagonal perovskites. As well, the field of geometrically frustrated magnetic materials is reviewed with emphasis on materials with the pyrochlore, spinel, and related structures. Phenomena exhibited by such compounds include colossal magneto‐resistance, charge and orbital ordering, half‐metallic ferromagnetism, low‐dimensional magnetism, spin glass, spin liquid, and spin ice ordering, among others.
Manganese: Organometallic Chemistry
Authors: Sweigart Dwight A. , Reingold Jeffrey A. 
Published: March 2006

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.
Manganese: The Oxygen‐Evolving Complex & ModelsBased in part on the article Manganese: Oxygen‐Evolving Complex & Models by Lars‐Erik Andréasson & Tore Vänngård which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Charles Dismukes G. , van Willigen Rogier T. 
Published: March 2006

AbstractIn this article, we give an overview of nature's singular biological process for producing oxygen gas by the oxidation of water in photosynthetic organisms. The harnessing of light to accomplish the splitting of water was arguably nature's most successful experiment in biological innovation. It enabled global proliferation of oxygenic photosynthesis and created the biogeochemical cycles of oxygen and carbon on earth. We review the atomic structure of the metalloenzyme, the photosystem II water splitting complex (PSII‐WOC), as revealed by X‐ray diffraction and spectroscopic techniques. We describe: 1) The electronic structure of its inorganic core, Mn4Ca1OxCl1–2(HCO3)y, based upon spectroscopic and magnetic susceptibility measurements, 2) the organization of the protein subunits as revealed by X‐ray diffraction and the role of select amino acid residues as revealed by site‐directed mutagenesis, and 3) the kinetic sequence of steps during assembly of the inorganic core to the cofactor‐depleted apo‐protein and the functional consequences of substitution of the inorganic cofactors. We use these data together with physico‐chemical data describing the formation of light‐induced intermediates, the exchange rates between substrate and free water molecules, the stoichiometry of electron and proton release and the activation energies to discuss possible mechanisms for photosynthetic water splitting. The chemistry of photosynthetic water splitting is energetically demanding and mechanistically complex. The lessons learned from nature have guided chemists seeking to incorporate these design principles within catalysts suitable for abiotic water splitting. We end with a description of the few synthetic manganese complexes that have been found to produce oxygen gas from water and discuss the chemical mechanisms by which they appear to function.