bluuebunny/crossref_metadata_2025 huggingface dataset:
Applying a simple water-energy balance framework to predict the climate sensitivity of streamflow over the continental United States
Authors: Renner M. , Bernhofer C.
Published: December 2011

Abstract. The prediction of climate effects on terrestrial ecosystems and water resources is one of the major research questions in hydrology. Conceptual water-energy balance models can be used to gain a first order estimate of how long-term average streamflow is changing with a change in water and energy supply. A common framework for investigation of this question is based on the Budyko hypothesis, which links hydrological response to aridity. Recently, Renner et al. (2011) introduced the CCUW hypothesis, which is based on the assumption that the total efficiency of the catchment ecosystem to use the available water and energy for actual evapotranspiration remains constant even under climate changes. Here, we confront the climate sensitivity approaches (including several versions of Budyko's approach and the CCUW) with data of more than 400 basins distributed over the continental United States. We first map an estimate of the sensitivity of streamflow to changes in precipitation using long-term average data of the period 1949–2003. This provides a hydro-climatic status of the respective basins as well as their expected proportional effect on changes in climate. Next, by splitting the data in two periods, we (i) analyse the long-term average changes in hydro-climatolgy, we (ii) use the different climate sensitivity methods to predict the change in streamflow given the observed changes in water and energy supply and (iii) we apply a quantitative approach to separate the impacts of changes in the long-term average climate from basin characteristics change on streamflow. This allows us to evaluate the observed changes in streamflow as well as to evaluate the impact of basin changes on the validity of climate sensitivity approaches. The apparent increase of streamflow in the majority of basins in the US is dominated by a climate trend towards increased humidity. It is further evident that impacts of changes in basin characteristics appear in parallel with climate changes. There are coherent spatial patterns with basins of increasing catchment efficiency being dominant in the western and central parts of the US. A hot spot of decreasing efficiency is found within the US Midwest. The impact of basin changes on the prediction is large and can be twice as the observed change signal. However, we find that both, the CCUW hypothesis and the approaches using the Budyko hypothesis, show minimal deviations between observed and predicted changes in streamflow for basins where a dominance of climatic changes and low influences of basin changes have been found. Thus, climate sensitivity methods can be regarded as valid tools if we expect climate changes only and neglect any direct anthropogenic influences.
Three-dimensional modelling of wave-induced current from the surf zone to the inner shelf
Authors: Michaud H. , Marsaleix P. , Leredde Y. , Estournel C. , Bourrin F. , Lyard F. , Mayet C. , Ardhuin F.
Published: December 2011

Abstract. We develop and implement a new method to take into account the impact of waves into the 3-D circulation model SYMPHONIE (Marsaleix et al., 2008, 2009a), following the simplified equations of Bennis et al. (2011) which use glm2z-RANS theory (Ardhuin et al., 2008b). These adiabatic equations are completed by additional parameterizations of wave breaking, bottom friction and wave-enhanced vertical mixing, making the forcing valid from the surf zone through to the open ocean. The wave forcing is performed by wave generation and propagation models WAVEWATCH III® (Tolman, 2008, 2009; Ardhuin et al., 2010) and SWAN (Booij et al., 1999). The model is tested and compared with other models for a plane beach test case, previously tested by Haas and Warner (2009) and Uchiyama et al. (2010). A comparison is also made with the laboratory measurements of Haller et al. (2002) of a barred beach with channels. Results fit with previous simulations performed by other models and with available observational data. Finally, a realistic case of energetic waves travelling over a coast of the Gulf of Lion (in the northwest of the Mediterranean Sea) for which currents are available at different depths as well as an accurate bathymetric database of the 0–10 m depth range, is then simulated. A grid nesting approach is used to account for the different forcings acting at different spatial scales. The simulation coupling the effects of waves and currents is successful to reproduce the powerful northward littoral drift in the 0–15 m depth zone. More precisely, two distinct cases are identified: when waves have a normal angle of incidence with the coast, they are responsible for complex circulation cells and rip currents in the surf zone, and when they travel obliquely, they generate a northward littoral drift. These features are more complicated than in the test cases, due to the complex bathymetry and the consideration of wind and non-stationary processes. Wave impacts in the inner shelf are less visible since wind and regional circulation seem to be the predominant forcings. Besides, a discrepancy between model and observations is noted at that scale, possibly linked to an underestimation of the wind stress. Lastly, this three-dimensional method allows a good representation of vertical current profiles and permits to calculate the shear stress associated with wave and current. Future work will focus on the combination with a sediment transport model.
Analyzing Integrin‐Dependent Adhesion
Authors: Mould A. Paul
Published: December 2011

In this unit, methods for the analysis of integrin‐dependent adhesion are described. Two major types of assays are commonly used for this analysis. The first are cell adhesion assays (as described in UNIT 9.1). A key application of this type of assay is to identify which integrin(s) mediate cell‐substrate interactions; a comprehensive list of antibodies suitable for this purpose is detailed. The second are solid‐phase assays in which purified integrins and integrin ligands are used. These assays can be used, e.g., to measure apparent affinities of integrins for different ligands and IC50 values of pharmacological inhibitors. Curr. Protoc. Cell Biol. 53:9.4.1‐9.4.17. © 2011 by John Wiley & Sons, Inc.
Actinides: Inorganic & Coordination ChemistryBased in part on the article Actinides: Inorganic & Coordination Chemistry by Grigorii L. Soloveichik which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Keogh D. Webster
Published: December 2011

The Inorganic and Coordination Chemistry of the 5f elements (Actinides) is intermediate between that of the transition metals and the 4f elements (Lanthanides). The first four members of the actinide series, Ac, Th, Pa, and U, are all naturally occurring but have unstable nuclei, making them radioactive. The other elements in the actinide series (transuranium elements or transuranics) are also radioactive and have been made by man through a variety of nuclear transformation processes, for example, neutron irradiation, atom bombardment, and radioactive decay. The actinide series may be broken into two separate groups, the light or early actinides (Ac–Am) and the heavy or late actinides (Cm–Lr). The chemical behaviors of these two groups are distinct. The light actinides are capable of being stabilized in a variety of oxidation states, for example, II to VII, and have been found to exhibit a significant degree of covalency in binding ligands. The heavy actinides are more reminiscent of the lanthanides in that the most persistent oxidation state is the trivalent and the bonding predominately occurs through ionic interactions. This difference has led to a substantial number of studies into the role of the 5f orbitals in structure and bonding of the actinides. One of the ions that has received a great deal of attention is the ubiquitous actinyl ion, AnO22+/+. This ion is the stable form for all aqueous complexes of the pentavalent and hexavalent light actinides. The oxo ligands are always found in a trans geometry and are strongly bound (triple bond) through a combination of σ‐ and π‐bonds with the 5f and 6d orbitals of the actinide metal center. While these strong covalent interactions exist with the axial oxo ligands, the bonding within the equatorial plane is primarily based on ionic interactions.

The ability of the light actinides to access multiple oxidation states leads to rich and, sometimes, complex electrochemistry. For example, under acidic conditions the reduction potentials for PuO
2
2+
, PuO
2
+
, Pu
4+
, and Pu
3+
are all close to 1 V. The physical manifestation of these close reduction potentials is an aqueous solution in which the plutonium can exist in four different oxidation states simultaneously. By careful control of the conditions, oxidation state pure solutions can be obtained for quantitative and qualitative studies. The binding affinities of the actinide ions to ligands follow the general trend An
4+
 > An
3+
 ∼ AnO
2
2+
 ≫ AnO
2
+
. Since the actinides are strong acids, the ions preferentially bond strong bases, for example, halides, oxygen donors, and so on. Owing to the greater degree of covalency in actinide complexes compared to the lanthanides, complexes with ligands having nitrogen, phosphorus, sulfur, and selenium donors are also found.
Alkali Metals: Inorganic ChemistryBased in part on the article Alkali Metals: Inorganic Chemistry by Francis S. Mair & Ronald Snaith which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Leung Wing‐Por , Wai‐Yan Ip Queenie
Published: December 2011

This article is updated to cover the literature in the area of inorganic chemistry of alkali metals since 1993. The advancement in instrumentation and spectroscopic techniques in the past decade has provided the researchers with more powerful tools for structure determination of compounds. In this respect, alkalides containing mixed‐sandwich complexes of alkali metal cations, complexes with dimers or chains of alkali metal anions, electrides with alkali metal ions intercalating in zeolite, and interstitial hydride enclosed by an unusual (Li+)8cubic cage have been found or studied by NMR. With the successful preparation of Na3N recently, its correct structure has been revealed. The exact composition of ‘NaB6’ has also been determined. The role of alkali metals in trielide clusters of traditional Zintl polyanions has been demonstrated. Trimetallic Li‐Na‐K amides, alkoxide compounds, and highly aggregated cage structures of lithium‐heavier alkali metal alkoxides have been reported.
Alkali Metals: Organometallic ChemistryBased in part on the article Alkali Metals: Organometallic Chemistry by Charles M. Lukehart which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Harvey Melanie J.
Published: December 2011

Organolithium complexes, like the organomagnesium Grignard Reagents, are important reactants in organic synthesis. The similarity in structure, bonding, and reactivity of organolithium and ‐magnesium compounds exemplifies the common chemistry exhibited by representative elements that appear in the same diagonal in the periodic table. Although much debate exists over the degree of covalency within lithium – carbon‐bonding interactions, the presence of some covalent character in LiC bonds of alkyllithium compounds is widely accepted. The bonding interactions within organoalkali metal complexes of the heavier alkali metals are generally considered to be strongly electrostatic or ionic in nature. This is supported by a large collection of evidence, consisting primarily of solution NMR data, single‐crystal X‐ray analyses, and gas‐phase computational studies. Many of the organolithium compounds are soluble in hydrocarbons, but organometallic compounds of the heavier group 1 metals generally require more polar solvents. In general, the reactivity of the alkali metals and the reactivity of the organometallic compounds of these metals increase as we go down the group or column. Organoalkali metal compounds are similar to, but more reactive than Grignard reagents. Organoalkali metal compounds are both air‐ and moisture‐sensitive and are sometimes pyrophoric. In addition, organoalkali metal compounds will react as Brønsted bases with protic reagents. Specific details regarding the synthesis, reactivity, and structures of various types of organoalkali metal compounds will be discussed.
Beryllium & Magnesium: Organometallic ChemistryBased in part on the article Beryllium & Magnesium: Organometallic Chemistry by E. Alexander Hill which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Saulys Dovas A. , Hill E. Alexander
Published: December 2011

Victor Grignard found in 1900 that solutions of organomagnesium halides form easily in the reaction of an organic halide with magnesium metal in diethyl ether. These Grignard reagents undergo useful reactions with many kinds of substrates. This discovery ushered in a new era in organometallic chemistry and provided chemists with a powerful and versatile reagent for synthesis of a wide variety of organic and organometallic compounds. This article discusses Grignard reagents in the broader context of organomagnesium chemistry. Preparatory methods surveyed include direct reaction of organic halides with the metal, exchange reactions with other organometallic compounds, as well as carbo‐ and hydrometalations. The current level of understanding of the mechanism of Grignard formation is summarized. The formation and reactivity of unusual species such as cluster Grignard reagents, for example, RMg4X (R = organic group, and X = halide) and polymagnesium compounds, for example, Ru[C5(MgCl)5]2are also discussed. The bonding and structure of organomagnesium compounds (as well as that of beryllium analogues) as described by diffraction methods, thermochemical data, colligative properties, spectroscopic (vibrational, nuclear magnetic, and electronic) measurements, kinetic studies, mass spectrometry, and theoretical methods are outlined.

The most prominent chemical property of organomagnesium compounds is their ability to deliver an effectively ‘anionic’ organic group with nucleophilic properties. As alkylating reagents, their important reactions include nucleophilic displacement of less basic leaving groups from saturated carbon atoms or other elements, addition to carbonyl groups and other unsaturated functions, and nucleophilic substitution at the acyl group of carboxylic acid derivatives. This broad array of substrates is surveyed, as are the effects of solvents and catalysts on reactivity. Less conspicuous reactions with wholly or predominantly inorganic substrates are also considered. Electron transfer reactions where organomagnesium compounds act as reductants are discussed.

Organoberyllium compounds are more difficult to prepare and are less nucleophilic than their magnesium counterparts. These features, together with their high toxicity, have limited their utility. Methods of preparation, as well as descriptions of bonding, structure, and reactivity patterns are presented. Of special note are recent advances in cyclopentadienyl beryllium chemistry, as well as the advent of beryllium–silicon chemistry.
Cadmium: Organometallic ChemistryBased in part on the article Cadmium: Organometallic Chemistry by Gerard Parkin which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Gupta Niladri Narayan , Atwood David A.
Published: December 2011

As a large, soft, heavy element, the chemistry of cadmium is marked by relatively weak bonding to carbon and other more electronegative atoms. Organocadmium compounds thus demonstrate diverse reaction chemistry. Furthermore, the large size and low valency of cadmium leads to interesting aggregated compounds. The reactivity and structural importance of organocadmium compounds and applications in solid‐state chemistry is offset by their high toxicity.
Carbon: Fullerenes
Authors: Crane Jonathan D. , Kroto Harold W.
Published: December 2011

The discovery of the fullerenes has revolutionalized the chemistry of carbon. For the first time a molecular form of the element carbon is available that can be manipulated and functionalized by the wide range of techniques available to molecular and materials scientists. In a very short space of time the fullerenes and their derivatives have been found to display many fascinating physical and chemical properties, and the astonishing pace of development in fullerene research is ample testimony to their great potential.
Chalcogenides: Solid‐State ChemistryBased in part on the article Chalcogenides: Solid State Chemistry by Patricia M. Keane which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Kanatzidis Mercouri G.
Published: December 2011

This article deals with the solid‐state chemistry of chalcogenides and describes mainly the developments during the past decade. The article is not exhaustive but is meant to give a broad set of examples of interesting compounds and solid‐state chemistry of these compounds so that the reader can obtain a reasonable and rounded view of the recent activities in this area. Further depth and additional information can be obtained from the available references.
Chromium: Biological Relevance
Authors: Vincent John B.
Published: December 2011

The biochemistry of CrIIIhas been a poorly understood field of endeavor; studies of the biochemistry of none of the other transition metals have been as problematic. Despite four decades of investigation, only recently has a clear picture of the role of Cr been defined potentially. The biologically important form is the trivalent ion, although not in the form of the purported glucose tolerance factor. Apparently, CrIIIis required for proper carbohydrate and lipid metabolism in mammals, although Cr deficiency is difficult to achieve. Conditions that increase circulating glucose and insulin concentrations increase urinary chromium output. Cr is excreted after an insulin challenge, probably in the form of the oligopeptide chromodulin. Chromodulin may be the key to understanding the role of Cr at a molecular level as the molecule has been found to bind to the activated insulin receptor, stimulating its kinase activity. A mechanism for the action of chromodulin has been proposed recently. The popular nutritional supplement chromium picolinate has been associated with potentially deleterious effects. The mechanism of toxicity of chromate (CrVI) is still an area of intense investigation.
Chromium: Inorganic & Coordination Chemistry
Authors: Theopold Klaus H.
Published: December 2011

The element chromium (Cr, atomic number 24) belongs to the first row of the transition metals, the properties of which are marked by partial occupation of their 3d orbitals. Together with molybdenum (Mo), tungsten (W), and unstable seaborgium (Sg), it makes up group 6 of the periodic table. Chromium is relatively abundant, occurring naturally in various oxide minerals (notably chromite, FeCr
2
O
4
). Because of its resistance to reaction with air and water, thin coatings of chromium are used to protect other metals against corrosion. Chromium features a great variety of accessible oxidation states; among these the +VI, +III, and +II states are of prime importance. Octahedral coordination compounds of Cr(III) are very stable and numerous; they have played a prominent role in the development of coordination chemistry. Hexavalent chromium is a very strong oxidant. It has traditionally been used in organic synthesis, but the inevitable metal wastes have discouraged its use as a stoichiometric oxidant. Cr(VI) is a known carcinogen, but there are no indications of adverse health effects of Cr(III); the latter is indeed an essential trace mineral implicated in glucose metabolism. Heterogeneous chromium catalysts play an important role in the catalysis of ethylene polymerization.
Cobalt: Inorganic & Coordination ChemistryBased in part on the article Cobalt: Inorganic & Coordination Chemistry by David A. Buckingham which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Blackman Allan G.
Published: December 2011

This article provides a summary of the important and interesting aspects of the inorganic and coordination chemistry of cobalt. A brief history of the element, detailing its discovery and historical uses, is given, and some general information concerning the properties of elemental cobalt is detailed. The general chemistry of cobalt is then outlined, including an overview of the common oxidation states found in inorganic compounds and complexes, a discussion of the stereochemistry, spectra and magnetism of cobalt complexes, and an outline of some analytical methods used for cobalt. The inorganic chemistry of simple cobalt salts is then described, and the coordination chemistry of cobalt, which constitutes the majority of the article, is then outlined in some detail. Coordination complexes of cobalt are detailed according to the oxidation state of the metal ion, with complexes ranging from Co(−I) to Co(V) discussed. Brief descriptions of the chemistry of each oxidation state are given, and specific examples are then outlined according to the nature of the ligand donor atom(s), with extensive references to both the primary literature and to review articles given. Thus, Co(I), Co(0), and Co(−I) complexes containing aliphatic, aromatic, and macrocyclic amine ligands, as well as Schiff‐base, porphyrin, and P‐donor ligands are discussed, while Co(II) complexes of carboxylate, heterocyclic, and oxygen‐derived ligands are summarized. Co(III) ammine and amine complexes are described in detail, while Co(III) complexes containing O‐donor ligands are also discussed. The few known Co(IV) and Co(V) complexes are outlined.
Cobalt: Organometallic ChemistryBased in part on the article Cobalt: Organometallic Chemistry by Ulrich Koelle which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Quisenberry Keith T. , Hanusa Timothy P.
Published: December 2011

Among the longest known families of organometallic compounds, those of cobalt display great diversity in their structures and oxidation states. The ligands accommodated in organocobalt compounds range from strong σ‐donors such as hydrides and alkyls, to π‐acid ligands such as carbonyls and phosphines. The carbonyl cluster compounds of cobalt are numerous and they play a major role in catalytic reactions of enormous industrial importance such as hydroformylation reactions (conversion of alkenes to aldehydes) and Pauson–Khand cycloaddition (production of cyclic ketones). Cobalt is an electron‐rich late transition metal, a property reflected throughout its organometallic chemistry. Thus, the carbonyl ‘hydride’ HCo(CO)4is actually a strong acid and does not have ‘hydridic’ (H−) properties. Similarly, cobalt does not complex to any group 15 or 16 heterocycles such as pyridine or thiophene. In contrast, boracycles are good ligands for cobalt in a sandwich complex because an electropositive atom such as boron incorporated in a π‐cyclic ring stabilizes the electron‐rich central metal. The cyclopentadienyl ligand is found extensively throughout organocobalt chemistry – not only in cobaltocenes, but also in half‐sandwich complexes of the type (C5H5)CoL2, where L is CO, alkene, alkyne, or phosphine. The (C5H5)CoL2complexes are useful in alkyne dimerization and trimerization. Cobaltocene itself ((C5H5)2Co) is easily oxidized to the extraordinarily stable 18‐electron cobaltocenium cation, [(C5H5)2Co]+. Cobalt can be incorporated into carborane cages, which have been found to be efficient extractors of radioactive metal ions such as90Sr and137Cs in water at low pH. Cobalamins, which consist of a cobalt central atom in a substituted corrin ring, are examples of naturally occurring organometallic compounds, and coenzyme B12was the first recognized example of a biological organometallic compound. Methylcobalamins play a role in biology, where they are found in microorganisms and can methylate mercury in the environment.
Coordination Numbers & Geometries
Authors: Clare Brian W. , Kepert David L.
Published: December 2011

The principles governing the adoption of specific coordination geometries by transition metal complexes is discussed with emphasis on monodentate and bidentate ligands. Geometric parameters describing the structures are noted as well as polyhedral rearrangements of such structures.
Electrochemistry: Applications in Inorganic ChemistryBased in part on the article Electrochemistry: Applications in Inorganic Chemistry by Robert H. Crabtree which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Holden Thorp H.
Published: December 2011

Because of the redox versatility of many transition metal complexes, electrochemical methods are an important part of the inorganic chemist's experimental repertoire. This article centers mostly on the use of cyclic voltammetry, where current is measured as the potential is varied linearly with time. Cyclic voltammetry is the primary method used by inorganic chemists, but many pulsed voltammetric provide complementary, and often useful, information. Theoretical methods now offer the means to calculate redox potentials of metal complexes, which can be correlated with values determined by cyclic voltammetry. Digital simulation techniques also now provide the ability to determine mechanistic information from voltammograms by directly calculating expected responses based on input mechanisms. Frontier applications of electrochemistry in inorganic chemistry involve the application of redox cycling to molecular memory.
Electron Transfer in Coordination Compounds
Authors: Endicott John F.
Published: December 2011

The transfer of an electron between a transition metal donor and a transition metal acceptor can be promoted by the absorption of either thermal or light energy. The thermal processes have been experimentally determined to span a range of about 1020in their ambient rates of electron transfer. The same molecular properties that determine the electron‐transfer reactivity also determine the correlated electron‐transfer absorption or emission band energy, band shape, and absorptivity. The relationships between the thermal‐kinetic and the spectroscopic observations are relatively simple when there is very little electron delocalization between the donor and acceptor, the weak‐coupling limit. This limit applies to most bimolecular electron‐transfer reactions of transition metals and to the spectroscopy of transition metal ion pairs; this is the limit treated well by Marcus theory. When the donor and acceptor are covalently linked, interactions of the donor and acceptor with the linker often increase the coupling in such a way as to enhance the reactivity and to alter the spectroscopy. Most of these linker‐induced changes of reactivity and spectroscopy can be treated in terms of perturbation theory‐based alterations of the behavior in the weak‐coupling limit. Reactivity in some very strongly coupled complexes seems to fall outside the standard theoretical framework; many such systems seem to implicate nuclear motions of the linker in facilitating the donor–acceptor electronic coupling. Extensions to biological, multicentered, and heterogeneous systems containing transition metal complexes are briefly considered.
Germanium: Inorganic ChemistryBased in part on the article Germanium: Inorganic Chemistry by Frank Glockling which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Qin Chao , Gao Lei , Wang Enbo
Published: December 2011

In this article, the basic physical and chemical properties, preparation, and applications of germanium and its related compounds are all described in detail. The whole chapter is divided into 12 sections, namely, introduction, analysis, the element, hydrides, boron derivatives, nitrogen compounds, phosphorus and arsenic compounds, oxygen‐bonded compounds, sulfides, selenides and tellurides, halides, metalloid‐ and metal‐bonded compounds, and polyoxometalates of germanium. In each section, some new development in the synthesis and applications of new compounds are included following the fundamental information.

In the introduction section, the discovery, distribution, effect on organisms, basic chemistry, and application of germanium are given briefly.

The analysis section gives a concise description of the main analysis processes.

The preparation, basic physical and chemical properties of metal germanium, and anionic germanium clusters are included in the element section.

In the following sections, different germanium compounds are described mainly according to the different valence germanium exhibits. Their fundamental synthetic routes, discovery and synthesis of new compounds, and the new development in the related fields are emphasized. In particular, contents concerning the construction of framework materials, the synthesis of polyoxometalates, which represent the tendency of development in inorganic chemistry, are presented comprehensively.

More than seventy equations are used to illustrate certain reactions, and detailed information of some important compounds and their synthetic routes are also given in the form of structures, schemes, and figures. Certain data, properties and structure information of germanium, and its compounds are listed in some tables.

Related articles are also given following the main content with the details explained in the text.

This article containing extensive contents about germanium should provide a basic resource for reference of the related studies. An explanation of the development of the recent germanium chemistry may provide insight into the exploration of new fields.
Halides: Solid‐State ChemistryBased in part on the article Halides: Solid State Chemistry by Gordon J. Miller which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Köhler J.
Published: December 2011

This review on binary metal halides demonstrates their enormous richness of structural topologies as well as compositions. It emphasizes thermodynamic stabilities, influences of size and electronegativity effects, the intricate balance of ionic and covalent metal–halide and metal–metal interactions, and effects of excess valence electrons of atoms with nonclosed shells, in order to outline relationships of structure and bonding. The most important structure types of the main group metal halides are given and pressure effects are discussed. Selected examples show the influence of the stereochemical activity of lone pairs of electrons in reduced halides. Halides of the transition elements are discussed according to their empirical formulas in order to correlate structure and properties with d electron concentration at the metal atoms, which are based on typical Jahn‐Teller distortions or the formation of metal–metal bonded units. Finally, a summary of the rare earth element halides is given.
Hydrodesulfurization & Hydrodenitrogenation
Authors: Angelici Robert J.
Published: December 2011

Hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) are large‐scale commercial processes that occur when petroleum feedstocks are treated with hydrogen (H2) at moderately high pressures and temperatures. During the reactions, the organosulfur and organonitrogen molecules liberate H2S and NH3. The process results in the production of hydrocarbon fuels with low levels of sulfur and nitrogen. Such fuels are necessary in order to prevent pollution of the atmosphere by sulfur and nitrogen oxides. The HDS and HDN processes are catalyzed by heterogeneous catalysts consisting of molybdenum and cobalt sulfides supported on alumina. Because it is experimentally impossible to determine details of the HDS and HDN processes as they occur on catalyst surfaces, detailed transformations that may occur on the catalyst are modeled by reactions that occur in transition metal complexes that can be fully characterized. As models for the adsorption of thiophenes, benzothiophenes, indoles, and quinolines on metal sites of the catalyst surface, these organosulfur and organonitrogen compounds are coordinated to metals in a variety of complexes. This coordination occurs through the sulfur or nitrogen atom or through π‐bonds in the hydrocarbon portion of the molecules and depends on the electronic state of the metal center. Once coordinated to a metal center, the organosulfur or organonitrogen compound is activated in ways that lead to the cleavage of CS and CN bonds, which are also reactions that occur in the heterogeneous HDS and HDN reactions. Patterns of reactivity of organosulfur and organonitrogen compounds in their metal complexes are used to propose detailed mechanisms for the steps that lead to the formation of H2S and NH3in the catalytic processes. The validity of these mechanisms has been tested in a range of isotopic labeling, spectroscopic, and reactivity investigations on the heterogeneous catalysts. Not only have the studies of organosulfur and organonitrogen complexes provided a basis for understanding and potentially improving the HDS and HDN processes, they have led to new approaches to the removal of sulfur and nitrogen and to new transformations of organosulfur and organonitrogen compounds.
Hydrogen: Inorganic Chemistry
Authors: Kakiuchi Masahisa
Published: December 2011

The properties of behavior of hydrogen and its isotopes, and the various applications of hydrogen are presented and discussed. The natural occurrence, preparation, use, and analysis of hydrogen are described. The atomic properties of protium (H), deuterium (D), and tritium (T) and the major physical properties of isotopic molecular hydrogen and isotopic water molecules are compared, and the distribution of deuterium and tritium in nature is geochemically discussed. Isotope effects concerning the vapor pressure and the fractionation factor of hydrogen and water molecules in equilibrium are explained, and are expanded in aqueous solutions. The chemical properties of atomic and ionized hydrogen, the reactions of molecular hydrogen, and the absorption and adsorption of hydrogen are compiled. The topics of the hydrogen spectroscopy, the ortho‐ and para‐hydrogen, the hydrogen in semiconductor, and the hydrogen energy are also compiled.
Iridium: Inorganic & Coordination Chemistry
Authors: Housecroft Catherine E.
Published: December 2011

This 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: 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: December 2011

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 Porphyrin Chemistry
Authors: Walker F. Ann , Simonis Ursula
Published: December 2011

This article reviews most aspects of the chemistry of iron porphyrins, from Fe(0) to Fe(V), including occurrence and roles of natural iron porphyrins (hemes) and their synthetic analogs, structures and electron configurations of iron porphyrins of all oxidation and spin states, π electron configuration of the porphyrin ring, synthesis of metal‐free porphyrins and other related macrocycles, insertion of iron into free‐base porphyrins and related macrocycles, the properties, reactions, uses and biological relevance of iron(0), ‐(I), ‐(II) porphyrins (the latter withS = 0, 1, and 2 spin state possibilities), of iron(II) porphyrin π‐cation radicals, of iron(III) porphyrins (withS = 1/2, 3/2, and 5/2 spin state possibilities), of iron(III) porphyrin and corrole π‐cation radicals, of iron(IV) porphyrins (including five‐ and six‐coordinate ferryl (FeO)2+, iron(IV) phenyl, carbene and hydrazine complexes, and the bis‐methoxide complex) and a comparison of iron(IV) porphyrins to iron(III) porphyrin π‐cation radicals, of iron(IV) porphyrin π‐cation radicals, and of the possible existence of iron(V) porphyrins. Included in the Fe(II) part are sections on addition of ligands to four‐coordinate iron(II) porphyrins, including equilibrium binding constants, photodissociation of ligands from PFeL2complexes, binding of small molecules (O2, CO, NO, HNO) to 5‐coordinate iron(II) porphyrins and design of porphyrin ligands that will mimic the active sites of heme proteins such as myoglobin and hemoglobin, the cytochromes P450 and nitric oxide synthases, and the nitrophorins and guanylyl cyclases. Included in the iron(III) part are sections on both 5‐ and 6‐coordinate high‐spin complexes and their similarities and differences, bridged or through‐space magnetically coupled complexes of high‐spin iron(III) porphyrins with other metal complexes as possible models for cytochrome oxidase and the assimilatory sulfite reductases, coupled oxidation of hemes by hydrogen peroxide or its equivalent, and the relationship of this reactivity to the reactions of heme oxygenase, iron(III) porphyrins as reduction catalysts, and photochemistry of iron(III) porphyrins, possible electron configurations of low‐spin iron(III) porphyrins, the phenomenon and possible electronic consequences of ruffling of the porphinato core in iron(III) porphyrins, the preferred orientation of planar axial ligands bound to low‐spin iron(III) porphyrins, NO complexes of iron(III) porphyrins, reduction potentials, equilibrium constants and rates of axial‐ligand addition and exchange, kinetics of axial‐ligand rotation and porphyrin ring inversion, kinetics of reduction and autoreduction of iron(III) porphyrins, electron self‐exchange between low‐spin iron(III) and iron(II) porphyrins, synthetic ferriheme proteins, and synthesis of five‐coordinate low‐spin iron(III) porphyrins having σ‐alkyl or σ‐aryl groups as axial ligands. The iron(IV) and iron(IV) cation radical sections discuss the high‐valent states of cytochromes P450 and related enzymes.
Iron Proteins for Storage & Transport & Their Synthetic Analogs
Authors: Lewin Allison , Le Brun Nick E. , Moore Geoffrey R.
Published: December 2011

This article reviews proteins involved in iron metabolism. Brief descriptions are given of the biological contexts for the proteins discussed but the main emphasis is on chemical and structural aspects of them.

Iron is essential to almost all forms of life, but its low bioavailability and toxicity mean that they require sophisticated mechanisms to transport it. Mammals acquire heme and nonheme iron via proteins in the gut wall, and transport it around the body using serum transferrin, for ferric iron, and hemopexin, for heme. Microbes have an active iron uptake mechanism involving small iron chelators called siderophores, for example, ferrichrome inEscherichia coli. Ferrichrome enters the cell via FhuA, a β‐barrel in the outer membrane. The periplasmic protein FhuD then transfers it to the FhuBC complex in the cytoplasmic membrane. FhuB forms a channel through which the ferric siderophore passes using energy supplied by FhuC. Once inside the cytoplasm the iron is removed from the ligand, possibly via reduction by FhuF. Some pathogenic bacteria have a similar system for heme uptake, secreting hemophores such as HasA, which can remove heme from hemoglobin. Other pathogens have outer membrane receptors that remove ferric iron from transferrin and transport it into the periplasm, where it is bound by ferric binding proteins that closely resemble a single lobe of transferrin.

Following its acquisition, iron needs to be stored safely. The most widespread form of iron storage is the ferritin superfamily, which includes ferritin, bacterioferritin, and Dps. Ferritin is found in bacteria, plants, and animals and is a large shell made up of 24 subunits within which up to 4,500 ferric ions can be stored as a ferrihydrite mineral core. Bacterioferritin is found in bacteria and is closely related to ferritin, but contains up to 12 heme groups bound between pairs of subunits, which may play a role in iron release or electron storage. The bacterial protein Dps is smaller than ferritin, with 12 subunits forming the protein shell, and can hold up to 500 ferric ions. All of these proteins contain dinuclear iron sites that catalyze the oxidation of ferrous iron. An alternative form of iron storage is frataxin, found in mitochondria. Although not related to ferritin, this protein has the ability to form large aggregates that can store up to 50 ferric ions per monomer in a mineral core resembling those of ferritins.
Iron–Sulfur Models of Protein Active SitesBased in part on the article Iron–Sulfur Models of Protein Active Sites by Akira Nakamura & Norikazu Ueyama which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Collins David J. , Zhou Hong‐Cai
Published: December 2011

In pervasiveness of occurrence and multiplicity of function, iron–sulfur clusters rival biological prosthetic groups such as hemes and flavins. The development of iron–sulfur cluster chemistry paralleled the founding and maturation of the field of bioinorganic chemistry. Starting from the first spontaneous self‐assembly of the [Fe
4
S
4
(SR)
4
]
2−
cluster in 1972, and the identification of the protein‐bound Fe
4
S
4
in the same year, the study of iron–sulfur models of protein active sites has evolved into a unique field in which synthetic inorganic chemistry now resembles the total synthesis of natural products in organic chemistry. Some of the models had been built before the crystal structure of the protein was determined. Almost all the models successfully replicated the topology and the electronic properties of the protein active sites. In this article, the models will be discussed in the order of their complexity, from single iron rubredoxin models to Fe
2
S
2
, Fe
3
S
4
, Fe
4
S
4
, and Fe
8
S
7
model compounds. In each section, the chemical synthesis of the model compound will be discussed first, followed by structure comparison and contrast, electrochemical properties, and biochemical activities. Since the major function of iron–sulfur proteins is electron transfer, and the oxidation state of the iron atom determines its reactivity, electrochemical and Mössbauer data will be tabulated in detail. Some of the recent developments in site‐differentiated, peptide, and all‐ferrous Fe
4
S
4
clusters will be reviewed. Recent studies in modeling the topology of the P‐cluster of nitrogenase will also be covered. The challenge posed by iron–sulfur proteins has inspired new iron–sulfur cluster chemistry. No other metal–nonmetal combination has produced more structural types than the iron–sulfur system; the majority of them have yet to be found in biological systems. However, the modeling of the P‐cluster and the FeMoco center of nitrogenase have posed a daunting challenge to the analog chemists.
Iron–Sulfur Proteins
Authors: Johnson Michael K. , Smith Archer D.
Published: December 2011

Iron–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.