bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ruthenium: Inorganic & Coordination ChemistryBased in part on the article Ruthenium: Inorganic & Coordination Chemistry by Bruno Chaudret & Sylviane Sabo‐Etienne which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Sabo‐Etienne Sylviane , Grellier Mary 
Published: December 2011

AbstractThis article presents an overview of the inorganic and coordination chemistry of ruthenium. Since the first edition of the encyclopedia in 1994, the field has seen a huge growth. We have attempted to select the most useful data for the readers not familiar with this topic and to detail the most promising systems for future developments. Key data and recent highlights are thus presented for seven classes of compounds incorporating the following ligands: (1) Halides: RuCl3·xH2O is by far the most useful starting material in ruthenium chemistry. (2) Oxygen‐donor ligands: this area is dominated by the chemistry of oxo complexes, with many applications in catalysis. (3) Sulfur‐donor ligands: potential applications are found in medicinal chemistry as antitumor agents and as radiosensitizers. (4) Nitrogen‐donor ligands: they represent the most important class of compounds in ruthenium chemistry. Supramolecular chemistry dominates, with photo‐redox processes and a wide range of applications being investigated from solar energy conversion to bioapplications. Ammines and bipyridines (and related ligands) are key ligands in this area. A great variety of inorganic architectures have been designed to assemble molecular machines and to favor interactions with DNA. (5) Phosphorus‐donor ligands: this class of compounds is at the origin of a rich organometallic chemistry, and the resulting complexes are often used as precursors in homogeneous catalysis. The design of new ligands for the improvement of catalytic performances is an active area of research. (6) Group 14 ligands: this field is dominated by the reactivity with silanes. New bonding modes, concepts, and applications have been disclosed. (7) Hydride ligands: the most recent developments concern the chemistry of dihydrogen complexes. The formation of dihydrogen bonds should have important consequences on the selectivity and stereochemistry in many catalytic processes. Finally, the last section is devoted to polynuclear complexes, with the new developments in the field of nanoparticles.
Scandium, Yttrium & the Lanthanides: Inorganic & Coordination Chemistry
Authors: Cotton Simon A. 
Published: December 2011

AbstractThe lanthanides are a block of elements with atomic numbers 57–71, which exhibit subtle gradations in their chemical properties, since the ionic radii gradually decrease across the series (the ‘lanthanide contraction’). In reactivity, they resemble the group 2 elements, but are much more diverse; although the aqueous chemistry is essentially that of the +3 oxidation state, the +2 and +4 states are significant for certain metals. The 4f orbitals are well shielded and play little part in lanthanide chemistry, so lanthanides have virtually no chemistry in the zerovalent state and do not form multiple bonds to atoms like N and O. As with the transition metals, lanthanide ions usually have a partly filled subshell (4f), but, in contrast, crystal‐field splittings are weak compared with spin‐orbit coupling, and thus spectroscopic properties of lanthanide complexes strongly resemble those of the free ions; sharp f‐f‐transitions in both excitation and emission spectra confer valuable properties upon certain ions. Lanthanides form a full range of binary compounds with nonmetals, especially the group 16 and 17 elements. The halides LnX3, in particular, demonstrate both the high coordination numbers and the lanthanide contraction. The complex chemistry in aqueous solution is dominated by ‘hard’ donors, especially oxygen‐based ligands (lanthanide ions have very high hydration energies), but ligands with other donor atoms, such as nitrogen, form stable complexes in nonaqueous solvents. The lanthanide aqua ion has a coordination number of 9, decreasing to 8 for the later metals; higher coordination numbers of up to 12 are possible with ligands with a small ‘bite’, such as nitrate. Many complexes exist of oxygen‐donor ligands such as THF and phosphine oxides, with formulae of the type [La(THF)nCl3] (n, e.g. 3, 4) and [Ln(R3PO)n(NO3)3] (n, e.g. 2, 3). Diketonate complexes are important; stable adducts with molecules like polyethers are often volatile enough to be MOCVD precursors. Bi‐ and tridentate N‐donor ligands like bipy and terpy form high coordination number complexes that often exhibit subtle variations in structure with choice of lanthanide and solvent. Low‐coordination numbers are achieved using very bulky amide, alkoxide, and alkyl ligands, when values as low as 2 and 3 are possible. Polyaminepolycarboxylic acids such as EDTA and DTPA form very stable complexes that are highly important in separating mixtures of the lanthanides and also, in the case of [Gd(DTPA)(H2O)]3−, as a contrast enhancing agent in MRI, one of an increasing number of applications that rely upon their electronic and magnetic properties. Yttrium has very similar properties to the later lanthanides, but scandium is significantly smaller. Although the first 3d metal, scandium is not a transition metal, but has significantly different properties, partly on account of its slightly greater size, forming complexes with higher coordination numbers (e.g. the aqua ion [Sc(H2O)7]3+). Its developing chemistry is that of a slightly smaller version of lutetium.
Scandium, Yttrium & The Lanthanides: Organometallic ChemistryBased in part on the article Scandium, Yttrium & The Lanthanides: Organometallic Chemistry by R. D. Köhn, G. Kociok‐Köhn, & H. Schumann which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Schumann Herbert , Fedushkin Igor L. 
Published: December 2011

AbstractThe group 3 metals scandium and yttrium and the 4f elements lanthanum to lutetium build up a big variety of organometallic compounds, in general with the metal in the oxidation state +3. Most of them are sandwich complexes Cp3Ln, Cp2LnX, and CpLnX2containing unsubstituted or substituted cyclopentadienyl ligands. In addition, cyclopentadienyl‐free organo rare earth compounds, like alkyl or aryl derivatives, alkenyl, allyl, alkynyl, hydrido, and carbene complexes, and organolanthanide compounds with indenyl, fluorenyl, cyclooctatetraenyl, or with heterocyclic ligands are described. Samarium, europium, and ytterbium form reasonable stable organic compounds in the oxidation state +2, whereas only a few rare earth organometallics with the metal in the oxidation state 0, +1, and +4 are known. All organo rare earth complexes are extremely sensitive to oxygen and water. The development of various synthetic methods as well as intensive single‐crystal X‐ray structure investigations made these highly reactive organometallic compounds available for use as organic synthons, efficient catalysts for polymerization, hydrogenation, hydroamination, and hydrosilylation as well as precursors for Metal Organic Chemical Vapor Deposition (MOCVD) and other material science applications.
Selenium Proteins Containing Selenocysteine
Authors: Böck August 
Published: December 2011

AbstractSelenium 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.
Sol–Gel Synthesis of Solids
Authors: Coradin Thibaud , Livage Jacques 
Published: December 2011

Abstract
The synthesis of glasses and ceramics via the sol–gel route is based on the inorganic polymerization of molecular precursors such as metal alkoxides. Precursor structure and reactivity can be chemically controlled via complexation or acid–base catalysis. Sol‐gel chemistry allows the powderless processing of glasses and ceramics, at much lower temperatures than usual solid‐state reactions. It provides a convenient and flexible access to nanoparticles, films, and fibres. Moreover, precursors are mixed at the molecular level and multicomponent materials can be formed. Thus, hybrid organic–inorganic materials have been made via the sol–gel route. The organic component can be used as a network modifier during the sol–gel synthesis and then withdrawn, allowing the formation of structured porous materials. It can also remain entrapped in the mineral matrix via weak interactions. Alternatively, organoalkoxysilanes allow covalent binding of organic moieties to silica networks. Such composites fill the gap between polymers and glasses and open new fields in materials science such as ‘sol–gel optics’ or bioencapsulation in mineral hosts.
Titanium: Inorganic & Coordination ChemistryBased in part on the article Titanium: Inorganic & Coordination Chemistry by Charles A. McAuliffe & Neil Bricklebank which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Valentine Ann M. 
Published: December 2011

Abstract
This article describes the chemistry of titanium, with special focus on its inorganic coordination chemistry. This field has a rich history and has flourished in the years since the first industrial processes for isolation of titanium were introduced. Covered are the discovery of the metal, some of the physical properties of titanium and its complexes, and the unique coordination chemistry of titanium in its various oxidation states. The metal is commonly found in the +4 oxidation state, in which it behaves as a hard Lewis acid. Titanium complexes with formal oxidation states +3, and, much less commonly, +2, 0, and −1 are also known. The oxides, sulfides, halides, and complex halides are discussed. Complexes with carbon, nitrogen, oxygen, silicon, phosphorus, sulfur, and arsenic donor ligands are described. Structures and spectroscopic data are given for selected compounds. Interest in the coordination chemistry of titanium has been driven by important applications in materials chemistry and in catalysis.
Vanadium: Inorganic & Coordination ChemistryBased in part on the article Vanadium: Inorganic & Coordination Chemistry by Elizabeth M. Page & Sherilyn A. Wass which appeared in the
Encyclopedia of Inorganic Chemistry, First Edition
.
Authors: Richards Raymond L. 
Published: December 2011

Abstract
The chemistry of vanadium and its complexes with various ligands is reviewed, following the format used in the corresponding article in the first edition of this Encyclopedia. The article begins with an update of the element itself. This is followed by a description of the binary compounds formed with hydride, halide, oxide, chalcogenide, nitride, and phosphide ligands. Compounds formed with carbide ligands are briefly mentioned, but thereafter carbon‐donor ligands are not included in this article.

Then follows a review of the coordination chemistry of vanadium, which, after a brief introduction, is grouped into sections according to the oxidation state of vanadium in the compounds under discussion. The first section describes compounds in low oxidation states, [vanadium(−1), vanadium(0), and vanadium(1)], in which nitrogen‐donor ligands such as N
2
and NO and tertiary phosphine ligands are prominent. The second section describes the coordination chemistry of vanadium(II). This section is subdivided according to the donor atom of the various ligands that bind the metal, that is, oxygen, nitrogen, and phosphorus ligands and other ligand types, such as halides. Vanadium(III) coordination complexes comprise the next section, which is subdivided according to oxygen ligands, nitrogen ligands, sulfur ligands, and halide and other ligands. It is to be noted that in general the compounds that have thus far been described tend to be oxidized rather easily to compounds of higher oxidation states.

The coordination chemistry of vanadium(IV), which comprises the next section, is dominated by the very stable VO
2+
(vanadyl) group and a separate subsection is devoted to coordination compounds that contain this grouping. The other subsections describe nonoxo complexes and halide, nitrogen, and sulfur and selenium ligands; the thiovanadyl group, VS
2+
is included in the last subsection. Oxygen‐donor ligands are also prominent in the chemistry of the highest oxidation state of vanadium(V), whose coordination chemistry is covered in the final section. Thus, separate subsections describe the coordination chemistry of the VO
3+
group, the VO
2
+
unit, and peroxo‐complexes. The remaining subsections describe nonoxo complexes, nitrogen, sulfur, and selenium ligands.

A feature of the development of vanadium chemistry during the years since the original article appeared has been the very large increase in the number of coordination complexes that have been prepared and structurally characterized. The content and relative sizes of the subsections of this article and the figures that are included reflect this trend.
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: December 2011

AbstractThis review surveys the chemistry of organovanadium compounds. Their syntheses and reactivities are described depending on the coordination‐binding mode.
Water &O‐Donor Ligands
Authors: Ogden Mark I. , Beer Paul D. 
Published: December 2011

AbstractThe chemistry of a range of O‐donor ligands is described, with an emphasis on the various ligand coordination modes and different structural types of the complexes formed. Water as a ligand is discussed along with the related hydroxide and oxide species. The structure, preparation, and reactions of alkoxide and aryloxide complexes are described. Similar coverage is provided for the diketone ligands. The rich variety of coordination modes of oxoanions, carboxylates, and related ligands, is emphasized. Complexation and structural chemistry of macrocyclic O‐donor ligands are discussed, particularly focusing on crown ether and calixarene metal complexes. The final section provides an overview of the chemistry of other commonly encountered η1O‐donor ligands.
Zinc Enzymes
Authors: Auld David S. 
Published: December 2011

AbstractA 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.
Alkaline Earth Metals: Organometallic Chemistry
Authors: Alexander Jacob S. , Guino‐o Marites , Zuniga Maria Felisa , Hahn Roger C. , Ruhlandt‐Senge Karin 
Published: December 2011

Abstract
The organometallic chemistry of the alkaline earth metals has undergone a renaissance during the last decade with exciting novel uses of the organomagnesium reagents in synthetic chemistry to significantly extend the utility of these well‐developed reagents. With the development of the organometallic chemistry of the heavier metals significantly lagging behind, and past work mainly focusing on and establishing π‐bonded metal–ligand systems, intense research efforts during the last decade have contributed significantly to expand the understanding of the organometallic compounds of these metals, establishing σ‐bonded organometallic compounds for the heavy alkaline earth metals. This improved insight did not only provide the basis for a more detailed understanding of the metal–ligand bonding characteristics, but also paved the way towards the successful applications of the compounds as polymerization initiators and in organic synthetic chemistry. This article summarizes some of the recent, exciting developments in regards to alkaline earth organometallics.
Biomimetic Synthesis of Nanoparticles
Authors: Slocik Joseph M. , Knecht Marc R. , Wright David W. 
Published: December 2011

Abstract

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.
Long‐Range Electron Transfer in Biology
Authors: Winkler Jay R. 
Published: December 2011

AbstractElectron‐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 cytochromecoxidase 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‐Mediated Protein Modification
Authors: Whittaker James W. 
Published: December 2011

AbstractPosttranslational modification of proteins is a general mechanism for regulating biological activity and expanding the functionality in this family of biopolymers. Metal ions have been found to be intimately involved in many of these protein‐processing reactions, whether as cofactors of processing metalloenzymes, intrinsic cofactors for self‐processing proteins, or protein‐targeting solution complexes. A broad range of covalent modifications have been identified as the products of these metal‐mediated reactions. Novel amino acid residues resulting from oxygenation, oxidation, or cross‐linking side chains play important roles in the structure and reactivity of proteins. In a number of cases, the modified amino acids serve as built‐in catalytic cofactors. Reactions of certain metal complexes have been implicated in biomedically important protein modifications, and synthetic complexes have been developed as probes of macromolecular structure. These links underscore the close connections between inorganic and biological chemistry.
Multi‐Heme Cytochromes & Enzymes
Authors: Pereira Inês A. C. , Xavier António V. 
Published: December 2011

AbstractMultihemeccytochromes and enzymes are a diverse group of proteins having several hemesccovalently bound to the polypeptide chain that are either enzymes involved in redox chemistry or electron transfer proteins. Most known members of this group are associated with the respiratory chains of proteobacteria. These proteins are characterized by a low amino acid to heme ratio, bis‐histidinyl coordination (with a few exceptions), and low redox potentials of the hemes. The hemes are usually tightly packed in close contact, allowing very fast electron transfer. Despite the absence of overall sequence identity between proteins, the hemes are found in quite conserved structural motifs, which tend to be organized in diheme pairs that are either parallel or perpendicular to each other. From the structures available, two families can be recognized in terms of the heme structural arrangement: the cytochromec3family where the perpendicular motif is predominant, and the hydroxylamine oxidoreductase (HAO) family where the stacked parallel motif alternates with the perpendicular motifs. Other multiheme cytochromes for which the structure is not yet available may be part of novel structural families.
Carbon–Carbon & Carbon–Heteroatom Activation
Authors: Crabtree Robert H. 
Published: December 2011

AbstractActivation involves binding of the intact CC or CX bond to the metal followed by CC or CX bond cleavage. Both aspects are considered here. The activation of CC bonds is facilitated by an enforced close approach of the CC bond to the metal or by the presence of a strong driving force such as a strained ring starting material or aromatization during the reaction. The reactivity order is: sp–sp > sp2–sp2 > sp3–sp3. The activation of CX bonds occurs by a number of mechanistic pathways depending on the system. Halocarbon complexes of type RXM are often intermediates and can be isolated in favorable cases.