bluuebunny/crossref_metadata_2025 huggingface dataset:
Iron Transport: Siderophores
Authors: Matzanke Berthold F.
Published: December 2011

Siderophores (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.
Ligand Field Theory & Spectra
Authors: Smith Derek W.
Published: December 2011

In any chemical environment – traditionally represented as a crystal field (CF), in which the donor atoms are represented by point charges – an
n
d 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 called
ligand field theory
(LFT). CF/LFT is important in the interpretation of the d–d spectra of complexes; the d–d states arising from cubic d

n

systems 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: December 2011

This 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: December 2011

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: Inorganic & Coordination ChemistryBased in part on the article Manganese: Inorganic & Coordination Chemistry by Charles A. McAuliffe, Stephen M. Godfrey, & Michael Watkinson which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Collomb Marie‐Noëlle , Deronzier Alain
Published: December 2011

This article covers the last 10 years of the inorganic and coordination chemistry of manganese at oxidation states (II), (III), (IV), (V), (VI), and (VII), as well as multinuclear compounds having oxidation states (II)–(IV) with both unitary and mixed valencies. The common ligands for manganese compounds involve the donor atoms nitrogen, oxygen, and the halogens while only few are known with other group V and group VI donors. One of the major areas of expansion has been the multinuclear complexes that are relevant to such diverse fields as metalloenzymes and single‐molecule magnets. Besides the small clusters, comprising two to four metal ions synthesized to model the structures and functions of manganese metalloenzymes, a lot of interest has been invested in larger clusters, not only for their biological relevance, but also for the development of materials with novel magnetic properties. Significant advances have been also been made in the chemistry of higher oxidation state manganese complexes (V), (VI), and (VII).
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: December 2011

In 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.
Mechanisms of Reaction of Organometallic Complexes
Authors: Atwood Jim D. , Rosenberg Edward
Published: December 2011

An overview of the mechanistic features of organometallic reactions is presented. The primary mechanistic types discussed are ligand substitution, oxidative addition, reductive elimination, and electron transfer. Each reaction pathway is discussed within the context of the common electron counts encountered for most organometallic complexes. Examples of how these common reaction pathways extend to polynuclear complexes are also presented. Although reasonable generalizations with regard to overall reaction rates and stepwise mechanisms using the electron count formalism can be made, many recent reports point out that the details of ligand and metal center structure can override these general trends. A considerable amount of quantitative rate data is provided and computational methodologies for understanding the observed rates are discussed.
Mercury: Organometallic ChemistryBased in part on the article Mercury: Organometallic Chemistry by Richard C. Larock which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Rais Daniela , Vilar Ramón
Published: December 2011

Over the past 10 years, a wide range of new organomercury compounds have been prepared and their reactivity extensively studied, leading to interesting applications in organic synthesis. The solvomercuration of alkenes is still the most widely employed organometallic reaction of mercury, although there have been important advances in the use of the mercury‐mediated ring opening of cyclopropanes. Several structural investigations of organomercurials have been recently carried out providing detailed information on the connectivity of a wide range of mono‐ and polymercuric complexes. In this article, an overview of the most important advances on the organometallic chemistry of mercury between 1993 and 2003 will be provided.
Metal Ion Toxicity
Authors: Martin R. Bruce
Published: December 2011

General principles of metal ion toxicity in humans are discussed including comparative stabilities with a variety of ligands and interdependencies among metal ions. Short reviews are presented for cadmium, mercury, lead, and aluminum.
Metallic Materials Deposition: Metal‐Organic PrecursorsBased in part on the article Metallic Materials Deposition: Metal–Organic Precursors by Herbert D. Kaesz, Alfred Zinn, & Lutz Brandt which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Winter Charles H. , Zheng Wenjun , El‐Kaderi Hani M.
Published: December 2011

This review describes metal‐organic precursors for the growth of metal‐containing thin films by chemical vapor deposition methods. The major emphasis is on precursors that have been reported since 1994, and corresponds to a time of major growth in this field. Progress in the development of metal‐organic precursors is documented for the main group, lanthanide, and group 4–11 elements. In the main group elements, there has been considerable research activity directed toward the identification of strontium and barium precursors, due both to the technological importance of mixed oxide phases and the inherent difficulties in obtaining volatile, complexes of these large metal ions. Aluminum, gallium, and indium have also been the subject of intense investigation, owing to the importance of many phases containing these elements. The group 4 and 5 elements titanium, zirconium, hafnium, niobium, and tantalum have been the subject of considerable precursor development activity, owing to the importance of several mixed oxide phases and the importance of zirconium and hafnium oxide for high permittivity gate materials in microelectronics devices. Growth of metal nitride films of these elements has also been an active area of research for use as barrier materials in microelectronics devices. The deposition of copper metal films from metal‐organic precursors is driven by the urgent need for copper metallization procedures in microelectronics device manufacturing. The current state of metal‐organic precursor development is presented for each of the other metallic elements.
MetallothioneinsBased in part on the article Metallothioneins by Milan Vašák & Jeremias H. R. Kägi which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Vašák Milan , Romero‐Isart Núria
Published: December 2011

Metallothionein (MT) is a generic name for a superfamily of ubiquitous low molecular weight cysteine‐ and metal‐rich proteins or polypeptides possessing sulfur‐based metal clusters. In these compounds, clusters are usually formed through the preferential coordination of d10metal ions by an array of closely spaced cysteine thiolate ligands. Their preservation in an increasing number of three‐dimensional structures of these proteins signifies the importance of this structural motif. The versatile and striking chemical reactivity of clusters in MTs and their unprecedented dynamics make this class of proteins highly unusual. A primary role of MTs has not been identified, and remains elusive, as further functions continue to be discovered.
Molybdenum: Organometallic ChemistryBased in part on the article Molybdenum: Organometallic Chemistry by M. David Curtis which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Flower Kevin R.
Published: December 2011

This article considers only compounds that contain a direct molybdenum‐to‐carbon bond. Because of the size of the topic and the large number of publications each year, the article gives a general overview of major current areas of interest in molybdenum‐centered organometallic chemistry. The material is presented in three major sections: σ‐ligand‐containing complexes, which covers alkyl‐, carbonyl‐, halocarbonyl‐, alkylidenes‐, and alkylidyne complexes, heavier group 14 analogs of alkylidene and alkylidyne complexes; π‐ligand‐containing complexes, which covers alkene‐, polyene‐, alkyne‐, phosphaalkyne‐containing complexes, along with π‐bound cyclic organic systems such as cyclobutadiene, cyclopentadienyl, and arenes; polymetallic complexes and multiply bonded systems are also discussed. Each section considers the major methods of preparation of compounds containing that ligand class and surveys the major types of reaction they undergo, both metal‐ and ligand‐centered, along with the factors that influence the products that form. Where data is available, solid‐state structural data are presented to aid in the discussion of the material presented.
Nitrogenase: Metal Cluster Models
Authors: Barrière Frédéric
Published: December 2011

This article reviews the synthesis and properties of inorganic clusters that model the iron–sulfur centers found in the nitrogenase enzyme. These sites are of the Fe
4
S
4
, Fe
8
S
7
, and MoFe
7
S
9
stoichiometry. The enzyme [Fe
4
S
4
]
2+/1+
center is well modeled by synthetic clusters bearing thiolate ligands at iron. However, the [Fe
4
S
4
]
0
state is stabilized in the enzyme and has not been reproduced in the laboratory so far. Recent progress in synthetic models of the Fe
8
S
7
P‐cluster is reported. One of its known structures can be obtained by self‐assembly from basic constituents, or synthesized in a stepwise fashion from smaller clusters yielding topological analogues. The most challenging cluster to model is the FeMo‐cofactor. This MoFe
7
S
9
center is the site of dinitrogen reduction to ammonia. The cluster also exists with vanadium or iron in place of molybdenum in alternative nitrogenases. It was shown only recently that the FeMo‐cofactor is centered on a light atom that is probably a nitrogen atom. Structural modeling of this center is limited. Only its molybdenum or heterometal end has been accurately modeled. Functional chemistry of good structural models, those with sulfur ligands and metal–metal bonds, only concerns the reduction of already partially reduced diazo substrates such as diazene or hydrazine.
Nitrogenase Catalysis & AssemblyBased in part on the article Nitrogenases & the Iron–Molybdenum Cofactor by Paul W. Ludden which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Hu Yilin , Schmid Benedikt , Ribbe Markus W.
Published: December 2011

Nitrogenases are metalloenzymes that catalyze biological N2fixation, in which dinitrogen is reduced to ammonia. The best‐characterized molybdenum nitrogenase is composed of the iron (Fe) protein that contains a [4Fe–4S] cluster and the molybdenum–iron (MoFe) protein that contains an [8Fe–7S] cluster (P cluster) and a [Mo–7Fe–9S–homocitrate] cluster (FeMo cofactor).

The catalysis of molybdenum nitrogenase occurs in a series of steps. First, the reduced Fe protein binds 2MgATP, undergoes a conformational change, and forms a complex with the MoFe protein. Then, coupled with the hydrolysis of 2MgATP, one electron is transferred from the Fe protein to the MoFe protein within the complex. This is followed by complex dissociation, which allows the enzyme to start the next cycle of electron transfer. Once a sufficient amount of electrons is accumulated on the MoFe protein, substrate reduction takes place.

The assembly of the molybdenum nitrogenase Fe protein involves thenifHand at least thenifS, nifU, andnifMgene products that are implicated in the [4Fe–4S] cluster assembly, while the assembly of the MoFe protein requires at least 15nifgene products and involves the biosynthesis and insertion of the FeMo cofactor into the MoFe protein.
Nucleic Acid–Metal Ion Interactions
Authors: Kazakov Sergei A. , Hecht Sidney M.
Published: December 2011

Nucleic acids (DNA and RNA) are actually salts (or complexes) of metal ions from a chemical point of view. It is impossible to separate the behavior of DNA and RNA from their interactions with metal ions. Metal ions are usually required to promote and stabilize functionally active or native conformations of nucleic acids, as well as to mediate nucleic acid‐protein interactions. However, certain metal ions can also cause structural transformation of nucleic acids, and induce their chemical modification and cleavage. Metal‐nucleic acid interactions are involved in nucleotide biochemistry; genetic information storage and transfer, and control of gene expression, as well as in mutagenesis and carcinogenesis. However, in most cases, it is not currently clear whether the observed effects actually result from direct metal ion‐nucleic acid interaction, since other species, such as specific proteins, may be mediators between the metal ion and the nucleic acid in these processesin vivo. Interest in metal‐nucleic acid interactions is also enhanced by studies of the mechanisms of antitumor activity of certain platinum metal compounds, finding metal ions in crystal structure of natural RNA molecules, studies of the mechanism of RNA catalysis and possible involvement of metal ions in origin of life, as well as by the use of metal ions as structural probes of nucleic acids and as biotechnology tools. This article does not attempt to be comprehensive, but rather presents selected examples to illustrate key facets of metal ion‐nucleic acid interaction. The focus is on the chemical and structural properties of both nucleic acids and metal ions relevant to their interactions. Nucleic acid‐metal interactions can be either nonspecific or dependent on the chemical nature, sequence, and structure of nucleic acids. However, the specificity of these interactions is dependent on structural and chemical properties of both the nucleic acids and the metal ions. Both nucleic acids and metal ions exhibit considerable complexity in their interactions, and such interactions could affect the chemical and biochemical properties of both species.
Osmium: Organometallic Chemistry
Authors: Shapley Patricia A.
Published: December 2011

Organometallic complexes of osmium include those with sigma bonds between the metal and the organic moiety, such as metal–alkyl complexes, or π bonds, such as metal–alkene complexes. The osmium alkyl complexes include homoleptic alkyls and complexes with ancillary carbonyl, cyclopentadienyl, arene, or alkene ligands. Because osmium complexes are stable in higher oxidation states than either ruthenium or iron, oxidative addition of CH bonds to form alkylidene and alkylidyne complexes is very common. Metal–ligand bonds also tend to be stronger in osmium complexes than in complexes of the lighter elements of this group. Because of the stability of OsOs bonds, there are many bimetallic and cluster complexes of osmium and these species have an extensive reaction chemistry. Selective oxidation reactions of unsaturated organic molecules dominates the catalytic chemistry of this metal. Mechanistic studies on the activation of molecular oxygen and oxygen transfer reactions by organoosmium complexes have provided insights into catalytic oxidation chemistry.
Oxides: Solid‐State Chemistry
Authors: McCarroll William H. , Ramanujachary Kandalam V.
Published: December 2011

This article is an overview of the solid‐state chemistry of oxides. It starts with a brief description of the periodic trends associated with compounds of oxygen and is followed by a discussion of the principle of the closest packing of spheres that can be used to describe ionic structures. An in depth description of several structure types, important in solid‐state oxide chemistry, follows, and covers the important binary structures as well as several ternary structures including the Perovskite, Spinel, Garnet, Pyrochlore, and Scheelite structures.

Selected special topics in solid‐state oxide chemistry include a discussion of crystallographic shear structures, defect oxides, and tungsten and molybdenum bronzes, intergrowth structures of which the high‐temperature superconductor YBa2Cu3O7is an example. The importance of structure‐property relations in oxides is illustrated by a discussion of metal–metal bonds in oxides, electronic conduction in a variety of oxides, and the catalytic properties of defect scheelites.

A lengthy discussion is devoted to the various means used by solid‐state chemists to synthesize oxides not only as bulk polycrystalline phases but as single crystals and thin films as well that are so important to electronic applications. The article concludes with a discussion of several important practical applications of oxides including magnetic oxides, oxide sensors, luminescent materials, ferroelectrics, CMR oxides, optical materials, ceramics, and refractory materials as well as a brief overview of other important uses.

Because this is a survey article, in depth discussion of many properties of oxides is not possible. However, many of these topics are covered in depth in other parts of the Encyclopedia and the reader will find the cross references helpful. A substantial list of references also provides a gateway to the solid‐state literature.
Palladium: Inorganic & Coordination Chemistry
Authors: Albéniz Ana C. , Espinet Pablo
Published: December 2011

Palladium is a group 10 metal used in the manufacture of exhaust autocatalysts in the automobile industry, in dental palladium alloys, in the electronics industry, in jewelry alloys, and in the manufacture of industrial catalysts. Although the latter represents only about 5% of Pd use, it is extremely important. A remarkable property of metallic palladium is its ability to absorb considerable amounts of hydrogen. The inorganic and coordination chemistry of palladium is mostly that of their oxidation states 0 and +2, but the oxidation states +1 and +4 are also well represented. Only in a few examples Pd can be guaranteed as Pd +3, while in others the ligands of Pd are noninnocent and the apparent oxidation state assigned to Pd can be deceptive. Only one Pd(V) and one Pd(VI) compound have been reported but not confirmed by independent research groups. The Pd(0) complexes reported include compounds with many possible ligands, which are known in [PdL4], [PdL3], and [PdL2] stoichiometries. The former are formed with conventional ligands and have the tendency to dissociate at least one ligand in solution, while the latter are formed with bulky ligands and are more reactive toward oxidative addition. In addition to Pd on carbon, colloids and polymer‐stabilized forms of Pd are catalytically important. All Pd(I) compounds reported feature PdPd or PdM bonds, with or without supporting bridges, displaying quite a large range of distances. Pd(II) compounds are commonly four‐coordinated square planar, but there are a considerable number of five‐coordinated compounds. Three‐coordinated Pd(II) compounds are not known. One doubtless case of a four‐coordinated tetrahedral (and accordingly paramagnetic) complex has been reported. Pdf2is a rare example of six‐coordinated Pd(II). Square‐planar Pd(II) fragments are building blocks in the construction of extended self‐assembled structures. Coordination tocis‐‘PdL2’ fragments can be used to define corners, whiletrans‐‘PdL2’ moieties can help build linear edges. Mononuclear complexes of Pd(III) can be stabilized by some tridentate macrocyclic ligands containing S and N as donors. A binuclear Pd(III) compound, displaying the shortest PdPd bond is also known. In both cases, the coordination number for Pd is six. Pd(IV) is not an uncommon oxidation state, although it is quite oxidant. Complexes with many different ligands, which show octahedral coordination are known.
Phosphorus: Inorganic ChemistryBased in part on the article Phosphorus: Inorganic Chemistry by Josef Novosad which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Kelly Paul F.
Published: December 2011

The element phosphorus was first discovered in 1669, and some measure of the growth of its uses and importance since then is evident from the fact that approximately half a million tons of the element are now produced annually; in addition, phosphorus‐based materials may be generated from naturally occurring phosphates, and for this reason over 130 million tons of such material are utilized per annum. Its importance to life means that natural phosphorus cycles occur; in addition, utilization of the element and its compounds is key to many industrial processes (producing products varying from pesticides to oil additives). In the laboratory, work has shown that many ‘naked’ phosphide anions can be prepared – these can even mimic organic systems, as in the case of the cyclo [P5]−ligand, which binds face on to metals in the manner of the cylcopentadienyl ligand. In addition, there are many examples of transition metal complexes of ligands containing only phosphorus; these range in size from just a single phosphorus atom to complex structures containing up to 14 atoms. Away from transition metal chemistry, phosphorus forms compounds with elements from all groups of the periodic table barring the noble gases; this article provides an overview of such compounds, with special interest in compounds that have an industrial use, that stabilize unusual bonding arrangements, or that are of current interest. In the process, it highlights the ability of the element to become involved in catenation and to form small cluster units, often with many PP bonds present. Thus, group 13 compounds of the element include the industrially important phosphides and a recently prepared new class of boron–phosphorus polymer. Silicon compounds of the element often exhibit unusual structures and some of these are illustrated and reference is made to multiple‐bonded systems, including the first example of a phosphabismuthene. Sulfides such as P4S10and halides such as PCl3and POCl3are of immense industrial importance and details of such processes and the consumption levels are provided. References to recent reviews on a range of pertinent topics are provided, including PSi chemistry, phosphides, phosphorus‐based polymers, phosphorus complexes of transition metals, phosphorus‐borane chemistry, phosphane ligands, organophosphorus chemistry, and phosphorus hydrides.
Photosynthesis
Authors: Staples Christopher R. , Blankenship Robert E.
Published: December 2011

Photosynthesis is a biological process in which light energy is captured and stored as chemical energy by organisms such as plants, algae and certain bacteria. The stored energy is then used to power cellular processes. Most organisms that perform photosynthesis utilize chlorophylls or bacteriochlorophylls, in conjunction with other pigments such as carotenoids, pheophytins, and bilins. The emphasis in this article will be on the aspects of photosynthesis that relate most directly to the subject of inorganic chemistry. The aspects presented include excited states, photochemical reactions, the role of metal ions in photosynthesis, the structures of pigments, electron transfer pathways, reduction potentials of components, chromophore absorption and fluorescence spectra, energetics, and kinetics. Recent crystal structures of photosystems I and II, the important enzyme cytochromeb6f, and antenna complexes and supercomplexes are presented and discussed.
Platinum‐Based Anticancer DrugsBased in part on the article Platinum‐Based Anticancer Drugs by Steven J. Brown, Christine S. Chow & Stephen J. Lippard which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Robillard Marc S. , Reedijk Jan
Published: December 2011

The chemotherapeutic agent cisplatin enjoys the status of one of the world's best‐selling anticancer drugs. As is the case with other chemotherapeutic drugs, however, cisplatin has its drawbacks, including intrinsic or acquired resistance and toxicity. Efforts to mitigate cisplatin's drawbacks have inspired the synthesis of myriad analogs, but with only a handful that have been shown to be acceptable for clinical application. Increased understanding of the mechanism of the action of cisplatin, as a result of decades of research, is leading to a more rational design of new platinum drugs. However, the incomplete puzzle of cisplatin's ways and the lack of a single decisive biological target for anticancer treatment still complicate the search for improved platinum drugs. This article gives a brief introduction to cisplatin, and subsequently summarizes and evaluates the development of cisplatin derivatives and possible new approaches.
Rhodium: Organometallic Chemistry
Authors: Mague Joel T.
Published: December 2011

A review of the major advances in the organometallic chemistry of rhodium covering the period 1993–2003 is presented. Highlighted are complexes containing N‐donor ligands such as triazacyclononanes and tris‐(pyrazolyl)borates, those containing vinylidene and allenylidene ligands, and the formation of metallamacrocyclic complexes. Also featured are results of detailed computational studies on the activation of CH bonds and the course of olefin hydroformylation and hydrogenation processes. Classes of organorhodium compounds covered include alkyl, aryl, vinylidene, allenylidene, alkynyl, and carbene complexes. Also reviewed are alkene, alkyne, isocyanide, and arene complexes, as well as carbonyl cluster compounds together with significant coverage of dinuclear complexes stabilized by bis(diphenylphosphino)methane ligands.
S
‐Donor Ligands
Authors: Collinson Simon R. , Schröder Martin
Published: December 2011

The chemistry of S‐donor ligands with metal centres is reviewed with emphasis placed on the structures and redox activity of the resultant complexes. Sulfides and thiolates bind to a wide range of metal ions. The oxidation of thiolates to sulfones and sulfoxides and the structures and chemistry of metal‐thiolene complexes are detailed. Thioethers are generally poor ligands for transition metal ions but macrocylic ligands afford stable complexes. Many metalloproteins contain metal–sulfur bonds and the structures of many of these have now been elucidated. This has sparked a renaissance in the synthesis of low‐molecular weight metal complex mimics.
Selenium: Inorganic ChemistryBased in part on the article Selenium: Inorganic Chemistry by Bernt Krebs, Stefan Bonmann, & Illenora Eidenschink which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Atwood David A.
Published: December 2011

Selenium is the first member of the group 16 elements O, S, Se, Te, and Po that shows some metallic character. The increasing metallic character in the series O, S, Se, Te, Po is reflected also in the lower electronegativity, in the less acid character of the oxides, and in the lower stability of the oxidation number +VI for selenium compared to sulfur. There is a large variety of compounds of SeII, SeIV, and SeVI with the electronegative elements N, O, F, Cl, and Br. Thus, there are six general types of compounds, and these will comprise the main sections in the article. They are cations, halides, oxides, haloselenates, oxohaloselenates, and the related compounds that form when both selenium and nitrogen are present in the molecule.
Silver: Organometallic Chemistry
Authors: Fackler John P.
Published: December 2011

The organometallic chemistry of silver and copper are in many ways similar. Simple alkyls are not thermally stable but fluorination of the hydrocarbon imparts considerable stability to the silver(I) products. Except for the special anion, [Ag(CF
3
)
4
]
−
, and derivatives such as Ag(CF
3
)
3
L, L = phosphine, which are stable, the fluorocarbon products generally are light and air sensitive, but less so than the nonfluorinated alkyls. Organometallic stability is increased when the silver is bonded to alkenes, alkynes, and other unsaturated species. Alkynylsilver compounds are generally polymeric solids. Alkenes π‐bond to the silver in Ag(I) salts. This feature has led to the well‐established use of silver catalysts for olefin epoxidation.
Solids: Characterization by Powder DiffractionBased in part on the article Solids: Characterization by Powder Diffraction by Anthony K. Cheetham which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Vogt Tom
Published: December 2011

This review article covers recent developments in X‐ray and neutron powder diffraction with an emphasis on the complementary nature of these two condensed matter probes. After a short summary of the basics of X‐ray and neutron scattering, examples of ‘mesoscopic’ structure investigations (i.e. particle size, strain) are presented followed by state‐of‐the‐art combined neutron and X‐ray high‐resolution powder diffraction studies of ‘real’ catalysts. Neutron and X‐ray powder diffraction studies in magnetic fields are highlighted and the reemergence of the total scattering approach using pair‐distribution function (PDF) analysis within the context of ‘nanocrystallography’ is discussed. Modern examples of high‐pressure crystallography using X‐ray and neutrons are given. A short outlook considers future directions in light of nanoscience and new X‐ray and neutron sources.
Solids: Computer Modeling
Authors: Catlow Richard
Published: December 2011

We review the role of computer modeling techniques in solid state chemistry. The basic aims and objectives of the field are summarised. We then describe basic aspects of the methodologies both of techniques based on interatomic potentials and electronic structure methods. We consider the range of applicability of each technique. Later sections of the chapter describe recent topical examples including modeling and prediction of crystal structures, simulation of nano‐cluster structures and energies and modeling of reaction mechanisms in heterogeneously catalysed reactions.
Stability Constants & Their DeterminationBased in part on the article Stability Constants & Their Determination by Harry M. N. H. Irving which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Hutton Alan T. , Linder Peter W.
Published: December 2011

This article is concerned with quantitative aspects of reactions in solution between metal ions and ligands to form complexes. The equilibrium constants of these reactions are usually calledstability constantsorformation constants. Formal definitions are presented of stability constants and a distinction is made between thermodynamic constants (activity quotients) and stoichiometric constants (concentration quotients). The practical difficulties of determining thermodynamic constants are discussed and the general resort to measuring stoichiometric constants and its implications are rationalized. The important idea and usefulness of formation curves for a given metal–ligand system are described. Mention is made of old‐fashioned curve‐fitting procedures for processing the relevant experimental data and references are given to the currently more important computer programs that have been developed for the purpose. Brief descriptions, especially of the underlying principles, are given of a selection of the experimental methods that have been developed for determining stability constants, that is, potentiometry, voltammetric methods (polarography and anodic stripping voltammetry), pH‐metry, competitive equilibria, use of cation exchange resins, liquid–liquid partition, spectophotometric methods, and nuclear magnetic resonance spectroscopy. Mention is made of a few other methods. pH‐metry is by far the most widely used and arguably the most sensitive and accurate of all the methods that have been developed. Justification for the considerable effort that has been, and continues to be, put into determining stability constants is presented in a section that summarizes the uses of stability constants. In particular, applications considered are to extraction metallurgy, the nuclear energy industry, analytical methods, and to medical, environmental, and industrial research. These applications all require stability constant values of high reliability and sources of critically evaluated published constants are referenced. Finally, a summary is presented of contributions that have been made to some fundamental ideas of chemistry arising from consideration of stability constant values.
SuperconductivityBased in part on the article Superconductivity by Jeremy K. Burdett which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Poole Charles P. , Farach Horacio A.
Published: December 2011

Superconductivity occurs in a material below its characteristic transition temperature. It is defined in terms of its two significant properties, that is, zero electrical resistance, and perfect diamagnetism. There are two characteristic lengths, the penetration depth for magnetic field penetration, and the coherence length, which measures the size of the supercurrent carriers called Cooper pairs. Supercurrents or persistent currents can flow indefinitely without loss. Elements are Type I superconductors, which totally exclude magnetic fields from their interior, and compounds are Type II superconductors, which partially exclude these fields. The application of an applied magnetic field greater than a critical field, and an applied electric current density exceeding a critical density, converts a superconductor to the normal state. Superconducting elements, alloys, and compounds are discussed, including borocarbides, Chevrel compounds, Laves phases, heavy fermions, A‐15 compounds, organics, alkali doped fullerenes, and cuprates or high‐temperature superconductors.
Supported Organotransition Metal Compounds
Authors: Hanson Brian E.
Published: December 2011

Supported transition metal complexes were first prepared in the 1960s as a potential method for the immobilization of homogeneous catalysts. Although this goal is yet to be commercially realized, the chemistry of supported complexes has given insight to the preparation of heterogeneous catalysts as, for example, in the use of discrete metal complexes as precursors to heterogeneous polymerization catalysts. The purpose of this article is to review the general methods for the immobilization of transition metals with examples of each type of immobilization technique.
Technetium & Rhenium: Inorganic & Coordination Chemistry
Authors: Pombeiro Armando J. L. , Guedes da Silva M. Fátima C. , Crabtree Robert H.
Published: December 2011

The inorganic and coordination chemistry of both rhenium and technetium is described in a condensed way with presentation of significant and typical compounds and reactions and applications in nuclear medicine and catalysis. After an Introduction, with properties of those elements and their sources, a description of binary compounds (for example oxides, sulfides, halides, and nitrides), their syntheses, structures, and selected reactions are given. This is followed by a treatment of the coordination chemistry of those metals, comprising hydrides, metal–metal bonded species and complexes with ligands coordinated by donor‐atoms mainly of the following periodic groups: 15 (commonly nitrogen and phosphorus, including dinitrogen, nitrile, nitric oxide and related ligands, hydrazides, diazenides, nitride, imides, pyrazolylborates, and phosphine ligands), 16 (mainly oxo, thio, and other O‐ or S‐ligands), and 17 (halide ligands); the metal–carbon (group 14) bond complexes are usually not covered since they are dealt with separately. Preparative methods, structures, and reactivities are illustrated for those types of complexes.

Selected complexes of
99 m
Tc and
186
Re (or
188
Re) are described and their applications in nuclear medicine illustrated, as radiopharmaceuticals normally for clinical diagnosis. The application of inorganic rhenium complexes in catalysis constitutes a currently expanding area of high potential and their use as catalysts for the following reactions is reviewed: oxygen atom transfer (OAT) and related reactions; isomerization or etherification of allylic or propargylic alcohols; Beckmann rearrangement of oximes; dehydration of primary amides and aldoximes; dehydrogenation of alkanes, unconventional reduction of aldehydes and ketones; aldol‐type reactions; and photo‐ and electrocatalytic reduction of carbon dioxide. A few catalytic applications of technetium compounds are also indicated.
Tellurium: Organotellurium ChemistryBased in part on the article Tellurium: Organotellurium Chemistry by William R. McWhinnie which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Laitinen Risto S. , Oilunkaniemi Raija
Published: December 2011

Chemistry of organotellurium compounds has developed very rapidly during the recent decades. Tellurium reagents find uses in synthetic organic chemistry. Organometallic complexes with tellurolato or telluroether ligands show potential application in the fabrication of new materials for electronic devices. The present review emphasizes the preparation and structural characterization of some main classes of organic tellurium compounds and their organometallic complexes that are deemed of interest for inorganic chemists.
Thallium: Inorganic Chemistry
Authors: Tóth Imre , Győri Béla
Published: December 2011

Classical knowledge of thallium inorganic chemistry is summarized in the article. The introduction consists of the history, occurrence and distribution, production, and use of this trace element. The properties of thallium(I) and thallium(III) are discussed by the short description of the most important inorganic compounds: hydrides, halides and pseudohalides, oxides, hydroxides, ternary, and more complex oxides, chalcogenides, salts with oxoanions, complexes with multidentate organic ligands, metal–metal bonded Tl‐complexes. The toxicity and the analytical methods are also shortly discussed.
Tin: Inorganic Chemistry
Authors: Wardell James L.
Published: December 2011

The alloying of copper with tin to produce bronze led to the formation of tools and weapons in what was later called the ‘Bronze Age’ from ≈2600–1500 BC. Since that time tin, in both the +2 and +4 oxidation states has figured prominently in inorganic compounds. This article will provide a summary of the types of inorganic compounds that tin forms, their spectroscopic characterization, and industrial uses.
Titanium: Organometallic Chemistry
Authors: Mintz Eric A.
Published: December 2011

The majority of titanium organometallic chemistry involves complexes in which the titanium is in its highest oxidation state (+4) with cyclopentadienyl derivatives as ancillary ligands. However, considerable chemistry has also been developed for complexes with titanium in the +3 and +2 oxidation state, with lesser amounts of chemistry developed for titanium in lower oxidation states (+1, 0). Since the early 1980s, chemists have placed considerable emphasis on the fine‐tuning of the structure and reactivity of titanium organometallic complexes. Particular emphasis has been devoted to tailoring the structure and reactivity of bis(cyclopentadienyl)titanium derivatives by incorporating electron‐donating, electron‐withdrawing, sterically demanding, or chiral substituents on the cyclopentadienyl ring. Considerable effort has gone into preparing ansa‐metallocenes with a wide variety of bridging groups and substituents to fine‐tune the reactivity catalysts prepared from them. In a similar manner, considerable effort has gone into the development of constrained geometry complexes. Several types of chiral substituted cyclopentadienyl, annulated cyclopentadienyl,ansa‐metallocenes, and constrained geometry complexes have been prepared and applied to olefin polymerization and organic synthesis. Additional efforts at modifying the structure and reactivity by focusing on varying the oxidation state or coordination geometry at the titanium center have expanded over the past decade.
Tungsten: Inorganic & Coordination Chemistry
Authors: McCleverty Jon A.
Published: December 2011

The inorganic and coordination chemistry of tungsten is described, being presented according to ligands and/or donor atom sets (halides, cyanides, and other ligands containing group IV atoms, ligands containing O, S, Se, Te, N, P, Sb, Bi, or, As donor atoms, hydrides, and borohydrido ligands) and are discussed in relation to the oxidation state. Special mention is made of metal–metal bonded dinuclear species, a brief description of polyoxoanionic species is given, and tri‐ and tetranuclear cluster compounds and some species of higher nuclearity, containing chalcogenide atoms, are described.