bluuebunny/crossref_metadata_2025_split huggingface dataset:
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 the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Winter Charles H. , Zheng Wenjun , El‐Kaderi Hani M. 
Published: March 2006

Abstract
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.
Molecular Orbital Theory
Authors: Czech Paul T. 
Published: March 2006

AbstractThis entry outlines the development of theoretical chemistry from its origins to the present highlighting important several theories, techniques, and applications to inorganic chemistry. The field has evolved from the series of postulates that provide the framework for quantum mechanics and which culminated in the Schrödinger equation proposed in 1926. Soon thereafter, the application to chemical systems began. Valence Bond Theory (VBT) and Molecular Orbital (MO) Theory were initial techniques for explaining what for chemists was of critical importance, that is, the nature of the chemical bond in molecules. Each approach is still useful today. Molecular Orbital Theory, however, has enjoyed wider applicability owing to being much more easily handled quantitatively. The explosive growth of digital computing capabilities over the last half‐century can no doubt be traced in part to the intensive number crunching requirements of this type. The article reviews the early work of VBT and MO theory, and the treatment of H2, homonuclear, and heteronuclear diatomic molecules in some detail. Sections concerning the important application of mathematical group theory conventions and several techniques that use the self‐consistent field approach define much of the terminology that is commonly used in the field. An up‐to‐date list of references and related articles provided interested readers with much more detail on the techniques and applications in this enormous field.
Molybdenum:MPT‐Containing Enzymes
Authors: Young Charles G. 
Published: March 2006

AbstractMolybdenum, an essential trace element for all forms of life, is found in a wide range of Mo‐MPT enzymes important in the metabolism of small molecules and anions of nitrogen, sulfur, carbon, chlorine, selenium, and arsenic, and in the global biogeochemical cycles of these elements. These enzymes feature active sites composed of a single (mononuclear) Mo atom coordinated by one or two MPT‐based ligands, L (MPT = ‘molybdopterin′ orMetal‐bindingPterin ene‐1,2‐diThiolate). These ligands contain a pyranopterin or simple pterin nucleus, an ene‐1,2‐dithiolate (dithiolene) unit, and a pendant phosphate group; in enzymes from prokaryotes, the phosphate is generally attached to a nucleotide, giving ‘dinucleotide’ forms of MPT. The dithiolene moiety functions as a bidentate S2‐donor ligand to Mo. The Mo‐MPT enzymes are classified into two broad functional types: oxotransferases and hydroxylases. The oxotransferases generally catalyze oxygen atom transfer reactions and fall into two families: the sulfite oxidase and dimethyl sulfoxide (DMSO) reductase families. Enzymes from these families contain square‐pyramidalcis‐[MoVIO2L(cysteinate)]−and distorted trigonal prismatic [MoVIO(AA)L2]−(AA = serinate, cysteinate, selenocysteinate, etc.) oxidized active sites, respectively. The hydroxylases all belong to the xanthine oxidase family and generally catalyze net insertion of oxygen into the CH bonds of heterocyclic aromatic compounds and aldehydes. They contain biologically unique, square‐pyramidal [MoVIOS(OH)L]−oxidized active sites featuring a catalytically essential terminal sulfido ligand. The sulfido ligand can act in a bridging capacity to Cu, as recently demonstrated for CO dehydrogenase. In most reactions catalyzed by Mo‐MPT enzymes, an oxygen atom is exchanged between substrate and water with concomitant consumption (for reductases) or production (for oxidases) of reducing equivalents (2e−, 2H+). Synthetic analogue (model) studies have produced complexes replicating or informing the composition, structures, spectroscopy, and chemistry of the enzymes. This account focuses on the Mo bioinorganic chemistry of the Mo‐MPT enzymes and selected synthetic analogues. It is divided into two main parts. Part 1 provides an overview of the enzyme systems, their distribution, roles, and essential chemistry, as well as a discussion of consensus structures and likely mechanisms. The genes and proteins involved in Mo trafficking and Mo‐cofactor biosynthesis are also briefly described. Part 2 summarizes important developments in the production of synthetic analogues, with a focus on new dithiolene, scorpionate, and other complexes sharing the structural, spectroscopic, or chemical attributes of the enzymes.
Nickel: Models of Protein Active SitesBased in part on the article Nickel: Models of Protein Active Sites by Michael J. Maroney which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Liaw Wen‐Feng 
Published: March 2006

AbstractDuring the past decade, structures and functions of the active sites have been established for the nickel‐based metalloenzymes present in the hydrogenases, ureases, carbon monoxide dehydrogenases/acetyl coenzyme A synthase, and methyl coenzyme M reductase. Roles of nickel in these Ni‐containing enzymes serve as catalytic or redox centers. Model compounds and various biophysical techniques have been lent to elucidate aspects of the structure and function (catalytic mechanism) of the Ni sites in these enzymes. Structures/functions of these Ni‐containing enzymes, biomimetic model compound studies, and the proposed catalytic mechanisms are presented.
Niobium & Tantalum: Organometallic ChemistryBased in part on the article Niobium & Tantalum: Organometallic Chemistry by David E. Wigley which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Wang Ruitao , Xue Ziling 
Published: March 2006

Abstract
This review highlights leading literature in syntheses, characterization, structures, and reactivities of organometallic complexes of niobium and tantalum between 1993 and early 2003. Such complexes include monometallic and bimetallic species. The applications of niobium and tantalum organometallic complexes in catalysis and metal‐mediated organic synthesis are discussed as well.
Nutritional Aspects of Metals & Trace ElementsBased in part on the article Nutritional Aspects of Metals & Trace Elements by Paul Saltman which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Yokoi Katsuhiko 
Published: March 2006

AbstractThe essential inorganic nutrients are dietary components that exert nutritional function when they are consumed as inorganic substances. Some essential inorganic nutrients such as selenium and iodine act as organic active constituents after metabolic conversionin vivowhen they are consumed as organic as well as inorganic substances. Inadequate intake of essential inorganic nutrients results in deficiency diseases and/or interruption of life cycles. The essential inorganic nutrients consist of the major elements (sodium, potassium, calcium, magnesium, chlorine, phosphorus, and sulfur) and the trace elements (iron, copper, zinc, manganese, cobalt, chromium, molybdenum, vanadium, nickel, arsenic, selenium, iodine, fluorine, silicon, boron, tin, cadmium, lead, rubidium, and lithium). Evidence of essentiality is limited for arsenic, boron, cadmium, fluorine, lead, lithium, nickel, rubidium, silicon, tin, and vanadium. If the requirement is less than 1 mg day−1for humans or 1 mg kg−1diet for animals, the inorganic nutrients are called ultratrace elements. Further investigation may increase the number of essential inorganic nutrients. Deficiencies of inorganic nutrients such as iodine, iron, and zinc occur worldwide. To prevent deficiencies and toxicosis, the US and other nations have established the Dietary Reference Intakes (DRIs) or the equivalents that are composed of reference values including Estimated Average Requirements (EARs), Recommended Dietary Allowances (RDAs), Adequate Intakes (AIs) and Tolerable Upper Intake Levels (ULs). Essential inorganic nutrients function in vivo through various modalities such as catalytic centers of enzymes, metabolic regulation, modulation of ion channels and receptors. The regulation and control of inorganic nutrients are a function of eight parameters: availability, solubility, permeability, ligand exchange, transport, assimilation, storage, and excretion. Excessive intakes, genetic abnormalities, and other etiologies cause pathologies of metal overload. Functions of selenium and nickel were reviewed. Selenium manifests antioxidant activity as an active site of glutathione peroxidase. Other important selenium‐containing proteins include thioredoxin reductase, iodothyronine deiodinases, selenoprotein P. Nickel occupies the metal centers of urease, carbon monoxide dehydrogenase, and other enzymes. Nickel deprivation results in impaired reproduction (rats and goats) and decreased spermatozoa motility and density (rats). It is our challenge to determine optimal intakes of inorganic nutrients for ensuring optimal health for all.
Organic Synthesis Using Transition Metal Complexes Containing π‐Bonded LigandsBased in part on the article Organic Synthesis using Transition Metal Complexes Containing π‐Bonded Ligands by Martin F. Semmelhack which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Morris W. H. , Sullivan Lisa M. , Wellons Matthew S. , Lukehart C. M. 
Published: March 2006

Abstract
A selective overview of reactions of transition metal π‐complexes pertaining to organic synthesis applications is provided. While reactions involving nucleophilic addition to pi‐coordinated ligands are emphasized, alkene insertion/elimination reactions and allyl coupling reactions are also discussed.
Osmium: Inorganic & Coordination Chemistry
Authors: Collinson Simon R. , Schröder Martin 
Published: March 2006

AbstractThe general features and coordination chemistry of Os are discussed in the context of the use of different ligand types to stabilize complexes of OsVIIIthrough to Os−II. The complexation chemistry with cyanide, N‐, P‐, O‐, S‐, and halide‐donor ligands is detailed. The asymmetric dihydroxylation and aminohydroxylation of alkenes, general coordination chemistry with macrocyclic and open chain ligands, porphyrin complexes, photophysical properties and electrochemistry of OsIIcomplexes of heterocyclic ligands and comparisons to their RuIIanalogues, and electron transfer in heterobimetallic and dendrimer complexes of OsIIare all highlighted.
Oxidation Catalysis by Transition Metal Complexes
Authors: Crabtree Robert H. 
Published: March 2006

AbstractOxidation catalysis is reviewed with emphasis on radical versus nonradical pathways, autoxidation, and mechanistic studies. Bioinorganic model catalysts are discussed, including the distinction between monooxygenase and dioxygenase pathways. Some organic synthetic applications as well as applications to green chemistry are discussed. Finally some organometallic oxidation catalysts are discussed.
Oxides: Solid‐State Chemistry
Authors: McCarroll William H. , Ramanujachary Kandalam V. 
Published: March 2006

AbstractThis 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.
Oxygen: Inorganic ChemistryBased in part on the article Oxygen: Inorganic Chemistry by Donald T. Sawyer which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Bharara Mohan S. , Atwood David A. 
Published: March 2006

AbstractThe present review will provide a systematic and complete coverage of the formation, chemical properties, and reactivity of a wide range of common oxygen‐containing species. These include dioxygen, ozone, hydrogen peroxide, oxide, superoxide, and hydroxide, as well as the radical forms of most of these species.
Palladium: Inorganic & Coordination Chemistry
Authors: Albéniz Ana C. , Espinet Pablo 
Published: March 2006

AbstractPalladium 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.
Paramagnetic Organometallic Complexes
Authors: Leznoff Daniel B. , Mund Garry 
Published: March 2006

AbstractThe synthesis, characterization, and reactivity of paramagnetic (or open‐shell) organometallic species are described. Many stable complexes featuring transition metals, lanthanides, and actinides have been reported. These systems, which are exceptions to the 18‐electron rule (or 16‐electron rule), are increasingly being used in the catalytic realm, and also have different reactivity patterns compared to their diamagnetic counterparts due to the presence of the unpaired electrons. The formation and subsequent stability of paramagnetic organometallic complexes in violation of the 18‐electron rule can be explained via molecular orbital theory in terms of (1) the use of π‐donor ligands (as opposed to the ubiquitous π‐acceptor ligands usually found in organometallic chemistry); (2) kinetic stabilization with sterically demanding ligands; (3) partially filled molecular orbitals being nonbonding or slightly antibonding/bonding. Although metallocene‐based complexes are probably the most well studied of all paramagnetic organometallic complexes, homoleptic σ‐alkyl complexes and other non‐Cp systems have also been explored. Such non‐Cp ancillary ligands include amido‐, alkoxo‐, and thiolato‐ligands, β‐diketiminate ligands, and tris(pyrazolylborate) ligands. f‐electron organometallic systems also utilize a similar range of ligands, but due to their larger size, they can accommodate more sterically congested coordination spheres; for example, Cp*3M complexes can be prepared, and they show unusual reactivity pathways.Open‐shell organometallic molecules are known to span a range of electron counts from 8–20. Nineteen‐electron organometallic complexes are of particular interest with respect to the location of the extra electron residing primarily on the metal or on the ligand (in this case, the complex is referred to as an 18 + δ system).The discussion of short‐lived paramagnetic organometallic systems revolves around 17‐ and 19‐electron radicals, and their use in catalytic processes and as ‘super reducing agents.’ Many reactivity pathways for such organometallic radicals (or ‘metalloradicals’) have been identified.Characterization tools for paramagnetic organometallic complexes, such as NMR and ESR spectroscopy, DFT calculations, and magnetic measurements are presented. Variable temperature NMR studies and2H NMR can be of significant use in interpreting paramagnetic NMR spectra. Solid‐state NMR spectroscopy of paramagnetic organometallic systems is still in its infancy. The applications of paramagnetic organometallic complexes span many areas including catalysis (e.g. olefin polymerization), synthetic organic chemistry, and the development of molecule‐based magnetic materials.
Phosphates: Solid‐State Chemistry
Authors: Attfield J. Paul 
Published: March 2006

Abstract

Phosphates contain oxyanions of phosphorus(V). The most common anion is the orthophosphate group PO
4
3−
, which is found in many solid phosphates including hydrated and acid phosphate salts. Oligomeric polyphosphate chains P

n

O

3
n
+1

(
n
+2)−

up to
n
= 6 and cyclophosphate rings P

n

O

3
n

n
−

up to
n
= 12 are also observed, and a unique cage ultraphosphate anion P
8
O
23
6−
is found in the Na
3
FeP
8
O
23
structure. Polymeric phosphate anions include the infinite chain catenaphosphate anion (PO
3
−
)
∞
and the ultraphosphate networks found in CaP
4
O
11
and the lanthanide MP
5
O
14
structures. Many compound anions and neutral frameworks such as silicophosphates, aluminophosphates, and molybdenum phosphates also exist. Phosphate species are characterized through PO stretching and bending vibrations in infrared and Raman spectroscopies, and by
31
P NMR. Phosphate structures are generally rigid, resistant to chemical attack, and (when anhydrous) insoluble and thermally stable. Some phosphate crystals have important physical properties such as ferrolectricity in KH
2
PO
4
(potassium dihydrogenphosphate, KDP). Diffusion of extra‐framework ions leads to potential uses of solid phosphates as ion exchangers and conductors, for example, NASICON based on NaZr
2
(PO
4
)
3
, and as cathode materials for lithium batteries. Vanadium phosphates are important selective oxidation catalysts. Large pore phosphates in which molecules can be adsorbed and undergo acid‐catalyzed reactions have been intensively studied. These materials are crystalline microporous solids such as aluminophosphates, or lamellar structures, typically based on α‐Zr(HPO
4
)
2
·H
2
O that can be pillared. This area of interest has led to the synthesis of many new organically templated metal phosphates in recent years, usually through hydrothermal reactions. Hydrated and acid orthophosphates can also be prepared in solution, and anhydrous phosphates are synthesized by direct high‐temperature reactions and from phosphate‐rich melts or fluxes. Slow cooling of melts is used to grow crystals, and quenching can result in many stable phosphate glasses. Phosphate anions do not absorb significantly in the UV‐visible region and so solid phosphates can also find use as optical materials such as phosphors, nonlinear crystals, for example, KTiOPO
4
, and lasers. Solid phosphates constitute many minerals, notably Apatites which are also found in living organisms as rigid components such as bones and teeth. Synthetic calcium phosphate biomaterials are used for bone implants.
Phosphides: Solid‐State Chemistry
Authors: Pöttgen Rainer , Hönle Wolfgang , von Schnering Hans Georg 
Published: March 2006

AbstractThe solid‐state chemistry of phosphides, phosphide oxides, and phosphide halides is reviewed. Phosphorus is outstanding, since no other element approaches phosphorus in the variety of homoatomic connected polyanions formed, as a result of its relatively low electronegativity and stereochemical features. The article covers the various synthesis techniques for solid‐state phosphides, the crystal chemistry, and chemical bonding. Besides the metal‐rich phosphides with pronounced metal–metal bonding, the large family of polyphosphides, which exhibits an unexpected wealth of chemical composition, is discussed. Furthermore, the largely varying magnetic, electronic, and catalytic properties are reviewed.