bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus: Inorganic ChemistryBased in part on the article Phosphorus: Inorganic Chemistry by Josef Novosad which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Kelly Paul F.
Published: March 2006

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 [P
5
]
−
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 P
4
S
10
and halides such as PCl
3
and POCl
3
are 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.
Phosphorus–Nitrogen CompoundsBased in part on the article Phosphorus–Nitrogen Compounds by Robert H. Neilson which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Haiduc Ionel
Published: March 2006

Phosphorus displays several oxidation states (+II,+III, +IV, and+V) and coordination numbers (from one to six), and with nitrogen (also two‐, three‐, and four‐coordinate) can form a broad variety of compounds (purely inorganic or organo‐N‐ or ‐P‐substituted). In addition to mononuclear PN compounds, many short‐chain, polymeric, and cyclic compounds based on molecular skeletons formed by PN alternation are known. There are numerous classes of phosphorus–nitrogen compounds, and this article makes an attempt to introduce the most important ones in the limited space available by selecting what seem to be the most illustrative examples from a very rich chapter of chemistry.
Phosphorus: Organophosphorus Chemistry
Authors: Engel Robert , Cohen JaimeLee Iolani
Published: March 2006

The chemistry associated with compounds bearing at least one carbon–phosphorus bond has been surveyed. This survey has been organized on the basis of the coordination about the phosphorus center, beginning with monocoordinated phosphorus and continuing through hexacoordinated phosphorus. Preparations, stereochemistry, and reactivity are principal topics considered.
Photochemistry of Transition Metal ComplexesBased in part on the article Photochemistry of Transition Metal Complexes by Lisa McElwee‐White which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Bitterwolf Tom
Published: March 2006

Photochemistry has evolved into a powerful tool for the highly selective generation of reactive intermediates in inorganic and organometallic chemistry. This review examines the state of the art in the examination of mechanisms of photochemical reactions utilizing techniques such as frozen matrices and fast time‐resolved methods. The application of photochemistry to the preparation of dihydrogen, alkane, and noble gas intermediates is reviewed along with the significance of these intermediates in the understanding of the mechanism of oxidative addition processes. Experiment and theory of charge transfer phenomena are extensively discussed along with the application of these processes to semiconductor and biochemical studies. Applications of photocrystallography to the examination of linkage isomers and very short‐lived excited state species are reviewed. Finally, a number of examples of the application of photochemical reactions, such as the photolysis of Fisher carbene species to generate ketenelike intermediates, to synthesis are discussed. The literature is reviewed to the end of 2003.
Photochemistry of Transition Metal Complexes: TheoryBased in part on the article Photochemistry of Transition Metal Complexes: Theory by Jeffrey I. Zink which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Daniel Chantal
Published: March 2006

The most significant developments in quantum chemistry and wave packet dynamics that provide the theoretical tools to study the electronic spectroscopy and photoreactivity of transition metal complexes are presented. The difficulties inherent to this class of molecules as well as the degree of maturity of the theoretical approaches are discussed. Recent applications in the chemistry of transition metal complexes are selected to outline and to illustrate the necessity for a strong interplay between theory and experiments.
Photoelectron Spectroscopy of Transition Metal Systems
Authors: Green Jennifer C.
Published: March 2006

Photoelectron spectroscopy measures the binding energies of electrons in molecules and solids. The article briefly considers experimental methods. A photoelectron spectrum is related to the molecular orbital structure of a system. Variation of the band intensities with photon energy gives information on the atomic orbital content of the originating molecular orbital. Band splitting may have a number of origins such as vibrational states, Jahn–Teller distortions, exchange splittings, and spin–orbit coupling. All of these provide additional information on electronic structure. Density functional calculations of ionization energies give good agreement with experiment. All these points are exemplified throughout and the article concludes with a number of case studies.
Photosynthesis
Authors: Staples Christopher R. , Blankenship Robert E.
Published: March 2006

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 the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Robillard Marc S. , Reedijk Jan
Published: March 2006

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.
Platinum: Inorganic & Coordination Chemistry
Authors: Crabtree Robert H. , Torrens Hugo
Published: March 2006

The article
Platinum: Inorganic & Coordination Chemistry
includes some historical highlights related to this metal as well as some properties and uses of platinum. Its inorganic and coordination chemistry is illustrated briefly through some specific chemical compounds and reactions. Binary compounds with halides, chalcogen, and related ligands are described. Platinum oxidation states 0 to IV are deal with on separated headings: compounds of Pt(0) predominantly with phosphine ligands; complexes of ‘monovalent’ platinum with PtPt bonds; Pt(II) with a large range of ligands; ‘trivalent’ platinum compounds and finally Pt(IV) bound to a variety of donor atoms. Nearly 70 references help the reader to follow specific topics.
Platinum: Organometallic ChemistryBased in part on the article Platinum: Organometallic Chemistry by Charles M. Lukehart which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Chen Jwu‐Ting
Published: March 2006

This article aims to describe the prominent advances of organoplatinum chemistry in the latest decade. Recent development in this field has been much advanced with the design of new ancillary ligands as well as new organic ligands. For the former, the polydentate cyclometallated ligands, tridentate pincer ligands, nitrogen‐donor ligands, and aminocarbenes are discussed. For the latter, in addition to the synthesis and structure of new organoplatinum compounds, a noteworthy growth is to exploit some of these compounds for luminescent materials. The content in this regard is brief since it has been covered as an independent article of this volume. Organoplatinum species with unprecedented bonding modes or new organometallic functionalities are discussed separately. The progress of nano sciences prompts the conceptual revolution in the whole frontier line of chemical research. Organoplatinum chemistry has been contributing in a profound way to construction of the new substances of large skeletons. Exploration starting from clusters and molecular assemblies to organometallic polymers, particularly with rational design, is addressed. Reactions involving the SiH, SiSi, CH, and CC bond formation or cleavage are crucial to hydrosilylation and alkane functionalization respectively. Platinum‐silylene chemistry accounts for a major breakthrough in synthetic chemistry. As to platinum‐hydrides that are mainly concerned in Pt(IV)‐state and are key intermediates in alkane activation, their syntheses and structures are discussed in Section 5. Platinum(IV)‐alkyls are the theme of Section 6. The reaction mechanisms of Pt(II)/Pt(IV) involving aqueous CH activation and other reactions or catalysis involving organoplatinum are summarized at the end.
Polonium: Organometallic Chemistry
Authors: Zingaro Ralph A.
Published: March 2006

The organometallic chemistry of polonium has received limited research effort. The element is very rare, and all of its isotopes are radioactive. Radioactivity causes rupture of the bonds between carbon and polonium. Also, because polonium is a heavy metal, chemical bonding to carbon is thermodynamically very weak. It is rare for an organometallic compound of polonium to be isolated in weighable quantities and characterized using the conventional techniques of organic chemistry. The identification of organopolonium compounds relies largely on chromatographic behavior and on the use of tellurium compounds having analogous chemical structures as reference compounds.
Rhodium: Inorganic & Coordination Chemistry
Authors: Jardine Fred H.
Published: March 2006

The element and its binary compounds are discussed, including specific discussions of the range of available oxidation states. Complexes of Rhodium(I), (II), and (III) receive attention, together with a discussion of nitrosyl complexes.
Ruthenium: Organometallic ChemistryBased in part on the article Ruthenium: Organometallic Chemistry by Ulrich Koelle which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: White Rosemary E. , Hanusa Timothy P.
Published: March 2006

In the slightly more than half a century that the organometallic chemistry of ruthenium has had time to develop, it has become clear that the metal's position as the ‘middle child’ of the Group 8 metals is richly reflected in its organometallic derivatives. That is, despite many similarities in the compounds of the iron–ruthenium–osmium triad, addition and elimination reactions of ruthenium, for example, are slower than those of iron but are more facile than those of osmium. Similarly, complexes with hydride and alkyl bonds are generally more stable for ruthenium than for iron, but the ruthenium compounds are often unstable or highly fluxional compared to analogous osmium species. Carbonyl cluster complexes are an important feature of organoruthenium chemistry, and mixed‐ligand carbonyl species with high nuclearity are known, in some cases with more than 10 ruthenium atoms. Interstitial carbides and nitrides are often encountered in ruthenium clusters, and carbonyl hydrides are of interest as hydroformylation catalysts (conversion of alkenes to aldehydes). The cyclopentadienyl ligand is found extensively throughout organoruthenium chemistry, and with a decomposition temperature around 600°C, the sandwich complex ruthenocene Ru(C
5
H
5
)
2
is among the most stable organometallic compounds known. The stability of ruthenocene and its derivatives allow them to be incorporated as labels into biomolecules such as peptides. Ruthenocene derivatives have also been studied as potential second‐order nonlinear optical materials, and they have played a central role in the development of 30 valence electron triple‐decker cations of the iron group. The high ligand field stabilization of Ru
II
enables combinations of π‐acceptor ligands together with even the hardest σ‐donors, such as carbonate, sulfate, or nitrate, and hence Ru
II
carbonyl and phosphine complexes are known with myriad coligand combinations having O, N, or S binding functionalities. In particular, the ability of the (η‐arene)Ru moiety to bind N‐ and O‐ligands has been used to complex various amines, imines, Schiff bases, and amino acids to generate diastereomeric salts, which can serve as chiral catalysts; they are valuable in stereoselective organic syntheses and in the production of biologically active compounds.
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: March 2006

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.
Selenium Proteins Containing Selenocysteine
Authors: Böck August
Published: March 2006

Selenium is incorporated in the form of the nonstandard amino acid selenocysteine into selected proteins of organisms belonging to all three lines of descent. The majority of these proteins, which contain selenocysteine in the active site, catalyze oxidation–reduction reactions and are involved in numerous biochemical and regulatory processes, which are indispensable for the organism. Because of the higher chemical reactivity of selenocysteine in comparison to cysteine, selenoenzymes display a greatly increased rate of catalysis. Apart from its biochemical function, selenocysteine is also unique since its incorporation is DNA‐encoded and its cotranslational insertion follows a route independent in many features from the path of insertion of the 20 classical amino acids. Selenocysteine, therefore, can be considered the 21st amino acid.
Short‐Lived Intermediates
Authors: Almond Matthew J. , Jenkins Samantha L.
Published: March 2006

Methods for the generation and detection of short‐lived intermediates are discussed. These include flow systems (where a steady‐state concentration of the intermediate is monitored), flash photolysis (where the intermediate is studied in real time using a very fast detection method), and matrix isolation (where the intermediate is preserved by trapping in a solid, inert host at low temperature and where conventional spectroscopic methods are used for detection). Many of the classical experiments utilizing these methods are described, but the relevance to modern chemical studies is also emphasized. The spectroscopic methods used to detect short‐lived intermediates are considered. These include nuclear magnetic resonance (NMR), electron spin resonance (ESR), microwave, infrared (IR), Raman, and ultraviolet‐visible absorption and emission spectroscopies. It is shown that IR remains the method of choice for matrix‐isolation experiments whereas flash photolysis work tends to rely mainly upon electronic spectroscopic techniques. The use of IR spectroscopy, using tunable lasers, for flash photolysis work (at least for slightly longer‐lived intermediates) is discussed. Finally two case studies are considered in detail. These are the photolysis of metal carbonyls and the formation of unusual main group compounds at high temperatures. These studies exemplify the procedures that have been used to investigate short‐lived intermediates in inorganic chemistry.
Silver: Inorganic & Coordination ChemistryBased in part on the article Silver: Inorganic & Coordination Chemistry by W. Ewen Smith which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Mak Thomas C. W. , Zhao Xiao‐Li
Published: March 2006

The present review is a complete rewrite of the original article in the first edition. The new version provides concise and up‐to‐date information on the inorganic and coordination compounds of silver in oxidation states ranging from subvalent to Ag(IV). Literature coverage is extended to October 2004, and pertinent references are listed for the convenience of the interested reader.

The presentation is organized under the following headings: 1. Introduction; 2. Subvalent silver compounds; 3. Silver(I) compounds (under subheadings: 3.1 Halides and pseudohalides; 3.2 Phosphorus donor ligands; 3.3 Nitrogen donor ligands; 3.4 Oxygen donor ligands; 3.5 Chalcogen donor ligands; 3.6 Silver‐rich compounds); 4. Silver(II) compounds; 5. Silver(III) and silver(IV) compounds; 6. Catalysis. The structural features of the compounds are described, and specific examples are illustrated with five figures.

For the most important +1 oxidation state of silver, particular emphasis is placed on recent highlights and advances in new areas such as double and multiple salts of silver, silver(I) polyhedra with encapsulated acetylenediide (C
2
2−
) species (symbolized as C
2
@Ag

n

), argentophilic Ag(I)⋯Ag(I) interaction in supramolecular assembly, halide‐centered Ag

n

cages, mixed‐metal clusters, and silver‐rich chalcogenide supercluster complexes. Modern application of inorganic silver catalysts, of both achiral and chiral types, to organic synthesis is presented with selected examples from the recent literature.
Solids: Characterization by Powder DiffractionBased in part on the article Solids: Characterization by Powder Diffraction by Anthony K. Cheetham which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Vogt Tom
Published: March 2006

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.
Stability Constants & Their DeterminationBased in part on the article Stability Constants & Their Determination by Harry M. N. H. Irving which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Hutton Alan T. , Linder Peter W.
Published: March 2006

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 called
stability constants
or
formation 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.
Sulfur: Inorganic Chemistry
Authors: Woollins J. Derek
Published: March 2006

The inorganic chemistry of sulfur is described. Oxides and oxy‐anions, halides are reviewed.
Sulfur: Organic PolysulfanesBased in part on the article Sulfur: Organic Polysulfanes by Ralf Steudel & Monika Kustos which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Atwood David A. , Zaman M. Kamruz
Published: March 2006

Organic polysulfanes are compounds of the type RSnR with n > 2. They may be chain‐like or cyclic. The organic residues (alkyl or aryl) are linked to the sulfur atoms via carbon atoms. In the literature these compounds are often termed as organic polysulfides, but the IUPAC recommended nomenclature is polysulfanes. Sulfur‐rich organic polysulfanes can be viewed as intermediates between organic and inorganic compounds. On one hand, they are characterized by organic substituents R, which terminate the sulfur chain or close this chain to form a ring. On the other hand, compounds with sulfur chains of three or more sulfur atoms are ‘inorganic’ enough to attract the interest of inorganic chemists who have contributed much to this area. Organic polysulfanes with up to 16 sulfur atoms in the molecules have so far been obtained as pure substances, but species with up to 35 sulfur atoms in a chain or ring have been prepared in mixtures. Organic polysulfanes play an important role not only in basic research and industry, they are also found as natural products in organisms and occur in the inanimate nature. The main importance of organic polysulfanes comes, however, from their role in the large scale industrial vulcanization of natural and synthetic rubber. In this article, the preparation, structure, modern analysis, basic reactions, natural occurrence, biological activity, and practical importance of organic polysulfanes with three or more neighboring sulfur atoms in a chain or ring have been presented.
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: March 2006

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.
Symmetry Point Groups
Authors: Bruce King R.
Published: March 2006

The symmetry of a molecule can be described by its symmetry point group, which is a mathematical group consisting of the symmetry operations of the molecule. This symmetry point group thus consists of the identity plus proper rotations, reflections, an inversion, and/or improper rotations.
Tellurium: Organotellurium ChemistryBased in part on the article Tellurium: Organotellurium Chemistry by William R. McWhinnie which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Laitinen Risto S. , Oilunkaniemi Raija
Published: March 2006

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: March 2006

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.
Thallium: Organometallic ChemistryBased in part on the article Thallium: Organometallic Chemistry by William S. Rees, Jr. & Gertrud Kräuter which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Pike Robert D.
Published: March 2006

The organometallic chemistry of thallium(I) is dominated by cyclopentadienyl complexes. These may be polymeric through bridging Cp arrangements or oligomeric as a result of Tl⋯Tl contacts. ThCp complexes are easily prepared and are highly useful Cp‐transfer agents. There are two known Tl(I) organometallics with direct TlC σ‐bonds; one is monomeric and the other is tetrameric due to Tl⋯Tl contact. A variety of Tl(I) π‐complexes are recognized. Bonding in the latter tends to be fairly weak.

Two R2TlTlR2dimers (R = silyl group) are known, but no such Tl(II) complexes are known for carbon ligands. The chemistry of organothallium(III) compounds is more extensive, encompassing such species as R3Tl, R2TlX, RTlX2(X = anionic ligand), and complexes of these species with additional ligands. A wide array of X‐ray crystal structures for Tl(III) complexes reveals monomeric, oligomeric, and polymeric arrangements, with bridging ligands being very common.

Thallium compounds are highly toxic and should be handled with great care. Volatile Tl species are of use in the chemical‐vapor deposition of superconducting phases. Finally, Tl(III) salts are fairly important reagents in organic syntheses, especially in oxidations and in ring expansion and contraction reactions.
Transition Metal Carbonyls: Infrared Spectra
Authors: Timney John A.
Published: March 2006

The number, pattern, and position of the CO‐stretching absorptions (ν(CO)) of transition metal carbonyls gives considerable information about molecular structure, symmetry, and bonding. This article deals with the processing of the basic data (number, frequency, and intensity of ν(CO) bands) to give useful information about carbonyl‐containing organometallic compounds via an ‘energy factored force field’ (EFFF). The reasons why the EFFF works so well and the relationships between different types of force constant within the EFFF are examined. The application of these force constants in elucidating molecular structure is discussed, together with the very successful ligand effect model that enables chemists to predict ν(CO) frequencies with remarkable accuracy.
Tungsten: Inorganic & Coordination Chemistry
Authors: McCleverty Jon A.
Published: March 2006

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.
Vanadium: Organometallic ChemistryBased in part on the article Vanadium: Organometallic Chemistry by Dieter Rehder which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Hirao Toshikazu
Published: March 2006

This review surveys the chemistry of organovanadium compounds. Their syntheses and reactivities are described depending on the coordination‐binding mode.
Zinc:DNA‐Binding Proteins
Authors: Pennella Mario A. , Giedroc David P.
Published: March 2006

Zinc‐containing nucleic acid‐binding proteins are ubiquitous in nature and interact with all types of nucleic acids, including ssDNA, duplex DNA, and RNA. The primary role played by these Zn(II) coordination complexes is to provide local or global stability to these proteins that function in transcriptional regulation, DNA metabolism, and nucleic acid packaging. These proteins are now broadly designated as zinc finger (zf) proteins. Six structural classes of zf proteins are discussed here that are distinguished from one another on the basis of the secondary and tertiary structure of the zf domain, the nature of the ligating side chains (Cys and/or His), and the linear spacing of amino acid ligands in the primary structure. These structural zinc sites are compared with metalloregulatory zinc coordination complexes found in metal‐sensing transcriptional regulatory proteins that control zinc homeostasis in bacteria (e.g.E. coliZurR and ZntR;S. aureusCzrA;SynechococcusSmtB), lower eukaryotes (S. cerevisiaeZap1), and mammalian cells (MTF‐1). Structural and functional comparisons of the bacterial zinc sensors with homologous sensors specific for other transition metal ions (e.g. Cu, Ni, Mn) and xenobiotics (e.g. Cd, Pb, and Hg) suggest that coordination number and therefore geometry are primary determinants of metal selectivity of metal sensor proteins in vivo.
Zinc Enzymes
Authors: Auld David S.
Published: March 2006

A remarkable mosaic of zinc‐binding motifs influence the function of proteins involved in all aspects of metabolism, providing evidence on the molecular level for the indispensability of zinc to growth and development and transmission of the genetic message. There are now about 400 three‐dimensional structures for zinc proteins, representing all six classes of enzymes and covering a wide range of phyla and species. These structures provide standards of reference for the identity and nature of zinc ligands in other proteins for which only the primary structure is known. Three primary types of zinc sites are apparent from examination of these structures: structural, catalytic, and cocatalytic. The most common amino acids that supply ligands to these sites are His, Glu, Asp, and Cys. In catalytic sites, zinc generally forms complexes with water and any three nitrogen, oxygen, and sulfur donors with His being the predominant amino acid chosen. Water is always a ligand to such sites. Structural zinc sites have four protein ligands and no bound water molecule. Twelve of the twenty‐two permutations of four Cys, His, Glu, and Asp ligands have been observed. Cys is the preferred ligand in such sites. Cocatalytic sites contain two or three metals in close proximity with two of the metals bridged by a side‐chain moiety of a single amino acid residue, such as Asp, Glu, or His and sometimes a water molecule. Asp and His are the preferred amino acids for these sites. The properties of both H‐bonding and hydrophobic amino acid ‘outer shell ligands’ and the secondary support structure of the zinc sites is important to the function, stability, and reactivity of the bound metal. The influence of zinc on quaternary protein structure has led to the identification of a fourth type of zinc‐binding site, protein interface. In this case, zinc sites are formed from ligands supplied from amino acid residues residing in the binding surface of two proteins. The resulting zinc site usually has the coordination properties of a catalytic or structural zinc‐binding site.
Zinc: Organometallic ChemistryBased in part on the article Zinc: Organometallic Chemistry by Gerard Parkin which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Grévy Jean‐Michel
Published: March 2006

Since the discovery of the first organozinc compounds by Sir Edward Frankland in 1849, the organometallic chemistry of zinc made remarkable advances and organozinc species have become essential tools for organic chemists. During the past decade, numerous new and modified procedures for the preparation of the title compounds have been published, rendering their synthesis easier, faster, and less expensive and giving higher yields. The coordination chemistry of organozinc derivatives has been subject of further interest and various intra‐ and intermolecular complexes with different donor ligands have been structurally characterized by X‐ray crystallography and spectroscopic methods. The accumulation of molecular structures, physicochemical studies, and computational calculations has led to a better understanding of the organozinc chemistry, and consequently to the design of new derivatives for specific applications. Even if the development of areas like the chemistry of organozinc anions and cations is still in its early stage, these compounds, which exhibit properties different than those of the parent organometallic species, appear to have promising applications in synthesis and catalytic reactions. During the past ten years, the chemistry of organo‐
gem
‐dizincio derivatives has also been the subject of much interest and progress. These reagents can form two carbon–carbon bonds in a one‐pot reaction and with high stereoselectivity. They became key reagents for organic chemists who want to combine multiple transformations in one operation. The importance of organometallic compounds of zinc can be seen in the growing number of their applications in synthesis. They are used in many reactions such as substitutions, additions to carbonyl compounds and unsaturated systems, cyclopropanations, and polymerizations. Furthermore, as a result of their low reactivity, they tolerate a wide variety of functionalities and perform most of the transformations with high regio‐ and enantioselectivity. After spending more than half a century in the shade of Grignard and organolithium reagents, organozinc reagents are becoming more and more important in modern chemistry.
Zirconium & Hafnium: Inorganic & Coordination ChemistryBased in part on the article Zirconium & Hafnium: Inorganic & Coordination Chemistry by Grigorii L. Soloveichik which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Kozak Christopher M. , Mountford Philip
Published: March 2006

The inorganic and coordination chemistry of zirconium and hafnium is described. The physical properties of the metals, as well as their isolation, purification, and commercial and industrial uses are discussed. A section on the binary compounds of zirconium and hafnium containing hydride and main group elements follows. Oxoacid salts of the two metals are described, as well as aqueous chemistry. Examples of zirconium and hafnium coordination chemistry are presented according to ligand type: molecular and silica‐supported hydride complexes; ionic and neutral halide complexes; complexes with oxygen donor ligands; complexes with nitrogen donor ligands; dinitrogen complexes; complexes with phosphorus and sulphur donors ligands; complexes with mixed‐donor ligands. Lastly, lower oxidation state inorganic, coordination, and cluster compounds are discussed.
Biomimetic Synthesis of Nanoparticles
Authors: Slocik Joseph M. , Knecht Marc R. , Wright David W.
Published: March 2006

Biological systems provide numerous examples of highly controlled biomineralization processes that result in stabilized nanoparticles with superior optical properties, crystallinity, dispersity, and morphology. This is best exemplified by the selective mineralization of ferrihydrite (FeOOH·3H
2
O) as a labile source of iron within the iron storage protein ferritin. Consequently, these processes have inspired the use of biomolecular templates to mediate and mimic the synthesis of nano‐materials with a remarkable degree of success. Biomimetic approaches to nanoparticle synthesis include the use of single amino acids, small synthetic peptides (3–18 residues), phage displayed peptides, combinatorial libraries, native proteins, and plant viruses. In the following, we present these biologically inspired templates and methodologies; in addition to describing nanoparticle characterization, resultant properties, and implications for the nanoscale synthesis of materials.
Metal‐Related Diseases of Genetic Origin
Authors: Sarkar Bibudhendra
Published: March 2006

In humans, there are several genetic disorders of metal metabolism. Wilson and Menkes diseases are genetic disorders of copper transport. The genes from these two diseases encode copper‐transporting ATPases. Mutations in Wilson disease gene cause toxic accumulation of copper in the cells whereas mutations in Menkes disease gene cause copper deficiency and lack of its incorporation in important copper enzymes. Wilson disease is treated by chelating agents such asD‐penicillamine and trientine and zinc, which inhibits absorption of copper from the intestine. Current treatment for Menkes disease is subcutaneous injection of copper‐histidine. Hereditary hemochromatosis, thalassemia, and aceruloplasminemia are major disorders of iron metabolism. The gene responsible for hereditary hemochromatosis encodes a protein, which is very similar to major histocompatibility complex on chromosome 6, that has been proposed to down‐regulate iron absorption. The disease is treated by weekly venesection of approximately 0.5 L of blood. Thalassemia causes severe iron accumulation as a result of disturbances in the synthesis of one or more of the globin chains of hemoglobin. The chelating agent used for the treatment is deferoxamine administered subcutaneously. The search for an orally administered iron chelator has been intensified in recent years leading to chemical trials of chelator such as deferiprone (L1). Aceruloplasminemia is caused by mutations in the ceruloplasmin gene resulting in iron accumulation in various tissues. Deferoxamine has been used to treat this disease. Acrodermatitis enteropathica is a genetic disorder of zinc metabolism. Mutations in the gene responsible for zinc transport result in insufficient absorption of zinc in this disease, which can be ameliorated by zinc supplementation. Several less common genetic disorders of metal metabolism are discussed briefly.
Long‐Range Electron Transfer in Biology
Authors: Winkler Jay R.
Published: March 2006

Electron‐transfer processes are vital elements of energy transduction pathways in living cells. A unique synergy between theory and experiment has produced an extraordinarily detailed understanding of the factors that regulate this ‘current of life’. Studies of Ru‐modified proteins have provided insights into the distance‐ and driving‐force dependences of intraprotein electron transfer rates. Electron transfer across protein–protein interfaces has been probed both in solution and in structurally characterized crystals. It is now clear that electrons tunnel between sites in biological redox chains, and that protein structures tune thermodynamic properties and electronic coupling interactions to facilitate these reactions. This research has produced an experimentally validated, electron tunneling timetable that predicts the time required for an electron to transfer across a specified distance in a protein. Many of the electron tunneling rates measured in cytochrome
c
oxidase and photosynthetic reaction centers agree well with timetable predictions, indicating that the natural reactions are highly optimized, both in terms of thermodynamics and electronic coupling.
Metal‐Based Drugs
Authors: Shaw C. Frank
Published: March 2006

Metallopharmaceuticals have a long history in the development of chemotherapy. The more recent success of cisplatin and six related Pt‐based antitumor drugs, and longer histories of chrysotherapy (gold treatments) for arthritis, bismuth antiulcer agents, and silver‐, antimony‐ and arsenic‐based antimicrobial agents demonstrate that the periodic table represents a potential wealth of medicinal agents to be explored and developed in the future. This article reviews the use of twelve elements (Ag, As, Au, Bi, Ga, Li, Pt, Ru, Sb, Sn, Ti, V) for a wide variety of diseases and disorders. The current state of research on particular applications varies widely – from promising treatments that have not yet reached the clinic to those that are well established empirically despite uncertain mechanisms of action. The array of antitumor agents licensed or in clinical trials includes compounds of As, Ga, Ru, and Ti, in addition to platinum. There are also exciting efforts to apply known treatments or biological properties to new diseases by taking advantage of extensive databases, for example, developing antitumor agents from organotin complexes that have long been used as fungicides and antifouling agents, and antimicrobial agents from gold complexes. The ability to modulate the properties of metal complexes by choice of the oxidation state (AuIvs AuIII; PtIIvs PtIV; VIII, VIV& VV, etc.) and design of the medical carrier ligands (e.g. 1,2‐diaminocyclohexane vs two ammine ligands for Pt antitumor agents) allows targeting of particular tissues or cells and balancing of lipophilicity, solubility, and reactivity to balance therapeutic activity against toxicity. Many, if not most, metallopharmaceuticals are prodrugs that undergo redox changes and/or ligand exchange reactions in vivo to generate the active species. Hence, research on metallodrug metabolism and pharmacology is as important as the initial medicinal screening of the agents.
Metallocenter Biosynthesis & Assembly
Authors: Mulrooney Scott B. , Hausinger Robert P.
Published: March 2006

Metalloproteins have been characterized intensively for decades, yet only recently has progress been made in characterizing the mechanisms of biological metallocenter biosynthesis and assembly. Here, we describe how cellular synthesis of metal sites makes use of several recurring themes, often with multiple themes combined into a single pathway. In the simplest situation, binding of a metal ion to a biological ligand occurs by reversible thermodynamic control. However, the prevalence of metallocenters deeply buried within macromolecules, the exceedingly low concentrations of free metal ions within cells, and the sophisticated structures of many metal‐containing active sites and cofactors provide evidence that alternative and more complex approaches also must exist. In some cases, metallochaperones are used to deliver the metal of interest to an apoprotein. In other cases the target protein undergoes posttranslational modification at the metal‐binding site, either prior to or after the metal is bound. Many metallocenters contain additional components that are added along with the metal ion or used to form a preassembled metal‐containing cofactor. Scaffolding proteins may be used to provide a framework for construction of the cofactor. Electron transfer reactions involving the metal, an added compound, or the protein ligand can participate in activation. Finally, molecular chaperones that bind to and alter the conformation of the target apoprotein may be utilized. In many cases, the function of the molecular chaperone is coupled to nucleotide triphosphate hydrolysis.