bluuebunny/crossref_metadata_2025 huggingface dataset:
Tungsten Proteins
Authors: Adams Michael W. W. , Roy Roopali
Published: December 2011

Tungsten (W, atomic number 74) and molybdenum (Mo, atomic number 42) are very similar metals chemically, and are equally abundant elements on this planet. Molybdenum has been known for decades to play an essential role in biology, and molybdenum‐containing enzymes are ubiquitous in both prokaryotes and eukaryotes. In contrast, tungsten appears to play a much more limited role in biological systems, and one that was established relatively recently. So far, tungsten‐containing enzymes have been found only in prokaryotes. The best‐characterized organisms with regard to their metabolism of tungsten are certain species of anaerobic archaea that grow at extreme temperatures (the hyperthermophiles) or produce methane gas (the methanogens), and anaerobic bacteria that produce acetate (the acetogens) or utilize acetylene. Of these, only the hyperthermophilic archaea appear to be obligately tungsten‐dependent. That is, they do not synthesize molybdenum‐containing homologs of key tungstoenzymes when grown on molybdenum rather than tungsten. Three fundamentally different types of tungstoenzyme have been characterized so far. The best characterized is the Aldehyde ferredoxin oxidoreductase (AOR) family, represented by aldehyde ferredoxin oxidoreductase. Hyperthermophilic archaea such asPyrococcus furiosuscontain at least four members of the AOR family of tungstoenzymes. These appear to play key roles in the metabolism of sugar and peptides. The second family, termed F(M)DH, contains two types of tungstoenzyme, formate dehydrogenase and formyl methanofuran dehydrogenase. These are involved in CO2metabolism in acetogens and methanogens, respectively. The F(M)DH members are much more complex enzymes than the AOR family and show no amino acid sequence similarity to them. The third family is represented by the enzyme acetylene hydratase (AH). It catalyzes the hydration of acetylene and is found in acetylene‐utilizing bacteria. Members of the AOR and F(M)DH family catalyze redox reactions of very low potential (≤−420 mV), in which tungsten undergoes a two‐electron redox reaction [W(IV) to W(VI)]. Crystal structures are available for two members of the AOR family and reveal that each subunit of the proteins contains a single W atom coordinated to two organic pterin molecules, which are bridged by a magnesium ion. An iron–sulfur cluster is situated near the W atom and is thought to be involved in electron transfer to it. The geochemical, ecological, and biochemical basis for tungsten‐ rather than molybdenum‐dependent organisms is discussed.
ZeolitesBased in part on the article Zeolites by Alan Dyer which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.
Authors: Williams Craig D.
Published: December 2011

This work looks at the natural formation of zeolites in our environment. It details the steps required in the laboratory to successfully manufacture zeolites, producing both novel and nature identical crystal forms. The classification of zeolites based on their aluminium content, pore/channel size is also covered in some detail. Finally the various physical and chemical properties that make zeolites so useful to everyday life are examined. These include their absorptive properties, ion‐exchange properties, desiccant properties, and catalytic properties.
Zintl Compounds
Authors: Kauzlarich Susan M.
Published: December 2011

The term Zintl phases was originally used to recognize contributions to the field of solid‐state inorganic compounds by Eduard Zintl. They were defined as a subgroup of intermetallic phases where the anions or anionic network could be considered formally to be valence satisfied. These compounds are made up of electropositive elements from groups 1, 2 that, in a formal sense, donate their electrons to the electronegative elements from groups 13, 14, and 15, which use them to form the correct number of bonds such that each element has a filled shell. The historical definition has been expanded from binary to ternary phases and enlarged to include transition metals and rare earth elements in some cases. The compounds that make up this class are described along with the corresponding Zintl anions arising from solution chemistry. Recent results in the field such as the use of Zintl phases for novel materials is also described.
Luminescence Behavior & Photochemistry of Organotransition Metal Compounds
Authors: Yam Vivian Wing‐Wah , Lo Kenneth Kam‐Wing
Published: December 2011

In this article, the luminescence and photochemical properties of a selection of organotransition metal compounds are reviewed and discussed. The examples are classified according to the identity of the carbon‐containing ligands, which include the carbonyl, isocyanide, cyanide, alkynyl, alkenyl, arene, aryl, alkylidene, alkylidyne, cyclometalating, and alkyl ligands. The luminescence and photochemistry of selected tungsten, molybdenum, and rhenium carbonyl compounds are described in this article, followed by some examples with the analogous isocyanide and cyanide ligands. The luminescence properties and potential applications of these systems are discussed. Transition metal complexes containing alkynyl ligands display a very wide structural diversity and catalytic properties, and many systems also show intriguing photoluminescence properties, especially those of rhenium(I), platinum(II), palladium(II), and the coinage metals. Studies focused on the photophysical studies and the excited‐state chemistry of selected alkynyl systems and related alkenyl, arene, and aryl complexes are outlined and discussed. Luminescent metal–carbon multiple bonded systems including the alkylidene and alkylidyne compounds have received relatively little attention, and examples have been confined to the complexes of molybdenum and tungsten. However, much effort has recently been devoted to exploring the interesting emission properties of alkylidene and alkylidyne systems with other metal centers such as rhenium, ruthenium, osmium, platinum, and coinage metals, which are outlined in this article. Some recent examples in the areas of cyclometalated complexes, especially those of rhodium(III), iridium(III), platinum(II), and gold(III) centers are highlighted in this article as many examples display impressive photophysical and photochemical behavior. Metal alkyl systems represent a special class of luminescent organometallic system due to their strong σ‐donating properties of the alkyl ligands, and the photophysical and excited‐state properties of some selected examples are described. Finally, luminescent organotransition metal compounds with application potentials in the development of new materials, photodevices, and sensory systems are summarized in various parts of this article.
Metallochaperones & Metal Ion Homeostasis
Authors: Culotta Valeria C.
Published: December 2011

There exists a large array of proteins that rely on metal ions such as copper and manganese for function and these so‐called metalloproteins are housed in diverse locations throughout the cell. It is imperative that each metalloprotein connects with the proper metal ion and also at the right time. How does this meeting of protein and metal occur in a specific and regulated fashion? The problem seems paramount when one considers the potentially toxic nature of metals. With the harm that metals can impose on biomolecules, these ions are never allowed to roam freely in the reactive form and, as such, the bioavailability of metals within cells is very limited. To overcome this problem, eukaryote cells have evolved with specific ‘metal trafficking pathways’ or designated routes a metal ion can follow once inside the cell. On one hand, the bulk of the metal may be subject to a dead fate involving sequestration by metal detoxification systems. On the other hand, a fraction of the metal destined for metalloproteins enters a trafficking pathway that involves both membrane transporters and ‘metal chaperones’ that directly insert the metal into the target metalloprotein. The bulk of current knowledge on metal chaperones and metal trafficking pathways has emerged from studies on copper and to a lesser degree on manganese. The work described herein focuses on paradigms developed for copper and manganese, with possible implications for other essential metals as well.
Semiconductor Nanocrystal Quantum Dots
Authors: Hollingsworth Jennifer A.
Published: December 2011

Semiconductor quantum dots (QDs) bridge the gap between cluster molecules and bulk materials. The boundaries between molecular, QD, and bulk regimes are not well defined and are strongly material dependent. However, a range from ∼100 to ∼10 000 atoms per particle can be considered as a rough estimate of sizes for which the nanocrystal regime occurs. The lower limit of this range is determined by the stability of the bulk crystalline structure with respect to isomerization into molecular structures. The upper limit corresponds to sizes for which energy level spacings approach thermal energy, kT. In this nanosize regime, the semiconductor energy‐ or band gap is dependent upon the particle size. This phenomenon is known as thequantum‐size effect, and it allows band‐gap‐dependent material properties to be tuned with particle size. Specifically, semiconductor absorption and emission wavelengths can be controllably blueshifted from their bulk semiconductor values over hundreds of nanometers.

Semiconductor quantum dots (QDs) have been prepared by a variety of ‘physical’ and ‘chemical’ methods. Here, we review the synthetic chemistry of QDs prepared by colloidal chemical routes. These QDs, known as nanocrystal quantum dots (NQDs), comprise an inorganic core overcoated with a layer of organic ligand molecules. The organic capping provides electronic and chemical passivation of surface dangling bonds, prevents uncontrolled growth and agglomeration of the nanoparticles, and allows NQDs to be chemically manipulated like large molecules with solubility and reactivity determined by the identity of the surface ligand. In contrast, with substrate‐bound epitaxial QDs prepared by physical deposition methods (e.g. molecular beam epitaxy and metal‐organic chemical vapor deposition), NQDs are ‘freestanding.’ In this discussion, we concentrate on the most successful synthesis methods, where success is determined by high crystallinity, adequate surface passivation, solubility in nonpolar or polar solvents, and good size monodispersity. Size monodispersity is critical as it permits the study and, ultimately, the use of materials‐size‐effects to define novel electronic, optical, and structural materials properties. Further, we examine many of the most significant contributions in the areas of NQD chemical surface modification (organic and inorganic), particle shape control, and phase control.
Periodic Table: Historical Aspects
Authors: Rouvray Dennis H.
Published: December 2011

The periodic table effectively embodies a summary of the entire realm of chemistry. Because of this, the table is one of the most important classifications of the natural world. However, the table could not be constructed before the concept of the chemical element had been clarified in the mid‐seventeenth century. Additionally, an ordering of the elements was not possible until a method had been devised of associating a number with each element, that is, the atomic weight or, nowadays, the atomic number. The periodic table evolved gradually over half a century, starting with the ordered triads of elements of Döbereiner in 1817 and culminating in the publication of the 63‐element table of Mendeleev in 1869. After its appearance, the table was confronted with several problems, including the accommodation of the noble gases, allowance for the existence of elemental isotopes, and the placement of the lanthanide and actinide elements. In spite of many such challenges, the periodic table has stood the test of time and is now widely viewed as one of the greatest achievements of the human intellect.
Low Coordinated Group 13 Chelates
Authors: Dagorne Samuel
Published: December 2011

Recent developments in the area of low‐coordinate group 13 chelates are the focus of this article. Emphasis is placed on the synthesis and reactivity of two new classes of compounds, that is, tri‐coordinate cationic chelates and monovalent two/three‐coordinate chelate species.

Unknown 10 years ago, tri‐coordinate chelate cations {L‐X}MR+(M = Al, Ga, In; R = Me, Et, Pr) could be obtained by reaction of the neutral precursors {L‐X}MR2with a strong Lewis acid such as [Ph3C][B(C6F5)4], provided an extremely crowded L‐X−bidentate ligand and an inert counterion are used. Reactivity studies on the Al derivatives show that these highly electrophilic species are potent Lewis acids as expected by the combination of the cationic charge and a low‐coordination number, but are less reactive than neutral AlR3compounds with regard to insertion of unsaturated substrates into the AlC bond.

The use of bulky tri‐ and bidentate ligands has also allowed access to unprecedented monovalent and monomeric low‐coordinate group 13 compounds. Tri‐coordinate Ga(I) and In(I) complexes incorporating a sterically encumbered HB(PzR, R′)−tridentate ligand were obtained and are quite stable. Similarly, the use of the very crowded HC(CMeNAr)2−andtBuNCCNtBu2−dinitrogen ligands with an appropriate synthetic methodology has opened the way to stable two‐coordinate and monovalent species: {HC(CMeNAr)2}M (M = Al, Ga) and the {tBuNCCNtBu}Ga−anion, respectively. Such species may behave either as Lewis acids or as Lewis bases due to the intrinsic properties of the metal center (a sextet configuration and the presence of a lone pair of electrons). Reactivity studies on these two‐coordinate complexes have just begun but have already permitted the synthesis of the first monomeric Al and Ga imide complexes {HC(CMeNAr)2}M(N‐Trip) (M = Al, Ga).

Finally, representative examples of recent new catalytic applications of tri‐coordinate Al(III) neutral species containing a chiral or achiral X22−‐type chelating ligand, used as catalysts, are mentioned.
Main Group: Multiple Bonding
Authors: Robinson Gregory H.
Published: December 2011

This chapter summarizes the many quite remarkable discoveries that have been made in recent years regarding multiple bonding of the heavier main group elements. While the general concept of multiple bonding is well established and easily embraced in organic chemistry, this is not the case for much of organometallic chemistry. The criteria that are routinely employed to assign double and triple bond character in organic compounds, that is, bond distance and bond strength, are of little significance in many cases involving the heavier main group elements. For example, the EE (E = Sn or Pb) double bond is both longer and weaker than the corresponding EE single bond. This chapter will discuss such seminal discoveries as the syntheses of the first digallyne (GaGa), dibismuthene (BiBi), and disilyne (SiSi). Central to these breakthroughs is the incorporation of sterically demanding ligand systems, which both stabilize and inhibit decomposition pathways of the heavier main group atoms.
Group 14 Multiple Bonding
Authors: Sasamori Takahiro , Tokitoh Norihiro
Published: December 2011

Multiply bonded compounds between heavier group 14 elements cannot exist as monomers under normal conditions owing to their inherent high reactivity, that is, they readily undergo oligomerization, oxidation, hydrolysis, and so on. The bulkiness of substituents on the reactive sites shows a great effect on the stabilization of such highly reactive compounds. Since the synthesis and isolation of the first stable disilene, Mes
2
SiSiMes
2
(Mes = mesityl), by R. West
et al.
in 1981, the idea of kinetic stabilization using bulky substituents have led to the successful isolation of several types of unsaturated compounds of group 14 elements, such as
heavy alkenes
(double bonds between heavier group 14 elements),
heavy ketones
(heavier group 14–16 double bonds),
heavy imines
(heavier group 14–15 double bonds),
heavy aromatics
(aromatic systems containing heavier group 14 elements),
heavy butadienes
, and triply bonded systems containing heavier group 14 elements, and so on. Now, unsaturated compounds containing heavier group 14 elements are no more imaginary species but are those of real existence even in the case of lead, the heaviest group 14 element, when they are appropriately protected by bulky substituents. The synthesis and properties of the kinetically stabilized unsaturated compounds containing heavier group 14 elements will be described in this section. Although a number of multiple bondings between heavier group 14 elements and transition metal elements have been reported so far, only unsaturated compounds containing main group elements should be considered here from the viewpoint of comparisons with carbon chemistry.
Metal Nanoparticles, Organization & Applications of
Authors: Schmid Günter
Published: December 2011

The need to organize metal nanoparticles in three, two, or one dimension(s) is linked with their properties, the use of which is only possible if they are organized. The most important properties of nonmagnetic and magnetic metal nanoparticles are therefore briefly discussed. Organization in three dimensions (3D) may happen by naturally happening crystallization processes or by linking the particles with the help of spacer molecules of various length and composition. 3D organized metal particles are quite well investigated and electron transport between the building blocks is satisfyingly understood. 2D arrangements result either by spontaneous self‐assembly from solution on appropriate supports, by guided self‐assembly, supporting the organization process, for instance, by means of pressure (Langmuir–Blodgett) or pre‐prepared surfaces, or the most attractive kind of organization, the aimed one, since it results in artificial structures that would be necessary if nanoparticles should find application in future nanodevices. Two routes to aimed structures have become known up to now: the dip‐pen nanolithography and the nanoelectrical modification of surfaces. Dip‐pen nanolithography uses the transport of special molecules from a moving AFM tip to suited surfaces. Chemical modifications of as‐prepared structures end up with formation of aimed patterns of metal nanoparticles. Nanoelectrical modification of CH3‐terminated surfaces, also using an AFM tip, give COOH functions that can further be modified to bind metal nanoparticles. Architectures performed by one of these methods simply depend on the software the AFM is moving on the surfaces.
Metal Analysis
Authors: Wrobel Katarzyna , Wrobel Kazimierz , Caruso Joseph A.
Published: December 2011

Measuring the concentration levels of trace and ultratrace elements in different samples is an important analytical task in environmental, biological, clinical, as well as industrial studies. Furthermore, the increasing recognition of species‐dependent behavior of elements in a given system has imposed the need for speciation analysis. Thus, the identification and/or quantification of individual compounds is required for elements in their naturally occurring forms, those produced and/or emitted from different anthropogenic activities, as well as the products of species degradation or biotransformation. The two most commonly used tools to deal with such analyses are plasma‐spectrometry techniques, namely inductively coupled plasma optical emission spectrometry (ICP‐OES) and inductively coupled plasma mass spectrometry (ICP‐MS). The suitability of these two techniques relies on their multielemental capabilities, high selectivity, wide dynamic range, high sample throughput, absence of chemical interferences, and easy coupling with different separation techniques. Consequently, applications of these techniques encompass both the determination of total element concentration and the specific detection of elements in different speciation schemes. In this article, the technical background of ICP‐OES and ICP‐MS is introduced, highlighting the capabilities and limitations of each technique. Different sample introduction systems are briefly presented and some applications for element analysis in inorganic and organometallic chemistry are reviewed.
Photoluminescence and Electroluminescence, Solid State
Authors: Deye Joel R. , Walters Keith A.
Published: December 2011

The measurement of photoluminescence or electroluminescence on solid samples can provide details on the electronic nature of the material in question. The majority of these measurements involve the examination of the electronic structure of semiconductors, especially those under consideration for use as light‐emitting diodes or photoelectric cells. The presence of defects in these materials (in the form of excitons and acceptor/donor centers) can dramatically alter the observed spectral properties. However, the technique is largely limited to electronic profiling, so significant structural information and sample morphology must be probed with complementary techniques. Basic instrumentation and techniques for recording these spectra are presented, along with special considerations for solid‐state samples. Numerous examples of recent literature reports utilizing this technique are also presented.
Rapid Scan, Stopped‐Flow Kinetics
Authors: Wang Rui‐Yong
Published: December 2011

One of the most frequently used rapid kinetics techniques is the stopped‐flow method. A major strength of rapid mixing methods is that they can be readily combined with a wide range of detection methods. Applications of stopped‐flow techniques, mainly stopped‐flow absorbance and fluorescence spectrometry, in the fields of inorganic and bioinorganic chemistry include kinetic measurement of ligand substitution, ligand binding and dissociation, redox reactions, and so on. The kinetic and thermodynamic parameters can be calculated with the aid of stopped‐flow methods. The general procedures for kinetic and thermodynamic studies by using stopped‐flow techniques are also discussed.
X‐Ray Crystallography
Authors: Guss Jules Mitchell
Published: December 2011

X‐ray crystallography is the most extensively practised and widely applicable technique for determining molecular structures. These may be relatively small coordination complexes or metalloproteins with masses exceeding 1000 kda. The accuracy of the structures may range from a few thousands of Ǻngstrom for a small molecules to a few tenths of an Ǻngstrom for a protein. The major limitation of the technique is the requirement for well‐diffracting crystals.
Electron‐Nuclear Double Resonance (ENDOR) Spectroscopy
Authors: Telser Joshua
Published: December 2011

Electron‐nuclear double resonance (ENDOR) spectroscopy is a magnetic resonance technique that was invented in the mid 1950s by George Feher, then at Bell Telephone Laboratories. The first applications of ENDOR were to problems in solid state physics, but beginning in the 1970s, and particularly since the late 1980s, ENDOR has been widely applied to bioinorganic systems. ENDOR is fundamentally an electron paramagnetic resonance (EPR) technique, however, it also has aspects of nuclear magnetic resonance (NMR) spectroscopy. Essentially, ENDOR consists of the monitoring of an EPR signal, while effecting NMR transitions. The EPR signal can be either a continuous wave (CW) signal or a pulsed, electron spin echo (ESE) signal, in both cases caused by the application of microwave energy to a sample in an external magnetic field. As with EPR itself, ENDOR can thus be either a CW or pulsed (time‐domain) spectroscopic technique. The NMR transitions are caused by the application of radiofrequency (rf) energy, as with NMR itself. NMR transitions only of nuclei magnetically (hyperfine) coupled to the paramagnetic center (i.e., the center giving rise to the EPR signal) affect the intensity of this EPR signal, whether CW or pulsed, and provide characteristic ENDOR spectra. As a consequence of its double resonance nature, ENDOR has a great deal of flexibility in spectroscopic parameters. The parameters that affect EPR signals, e.g., microwave power, can also play a role in ENDOR spectral appearance. Additionally, there are parameters relevant to the NMR aspects of ENDOR that affect ENDOR spectra. In both CW and pulsed ENDOR there is experimental flexibility, which is described here. As a result, ENDOR spectroscopy can provide detailed information on multiple, magnetically active nuclei that comprise a paramagnetic center in a bioinorganic system. This information includes identification of such nuclei and metrical information on their relation to the paramagnetic center. This article uses a multifaceted case study to illustrate the application of ENDOR spectroscopy in bioinorganic chemistry. Specifically, the case study describes the application of multinuclear (1, 2H,13C,57Fe,95Mo) CW and pulsed ENDOR to enhance our understanding of the iron–molybdenum cofactor in nitrogenase. ENDOR allows identification of the constituent metal ions and their formal oxidation states, and identifies the nature of the substrate analog or inhibitor binding to the cluster. In combination with resting state structural information, and computational and model system studies, ENDOR can provide a structural picture of the intermediates in nitrogen fixation.
Freeze‐Quench Kinetics
Authors: de Vries Simon
Published: December 2011

Rapid‐mixing, rapid‐freezing techniques are employed for the study of enzyme or chemical catalytic mechanisms. The techniques aim to provide electronic and molecular structures of transient intermediates formed during the reaction by means of spectroscopic analyses of the rapidly frozen samples. Briefly, the mixing‐sampling procedure consists of the rapid mixing of two reactants, for example, enzyme and substrate, followed by rapid freezing of the mixture in a liquid cryo‐medium or on a cold plate to quench the reaction progress. The resulting frozen powder is subsequently sampled and made available for further low‐temperature spectroscopic analyses such as UV‐Vis spectroscopy, multifrequency Electron Paramagnetic Resonance (EPR) spectroscopy, Electron Nuclear Double Resonance (ENDOR) spectroscopy, Electron Spin Echo Envelope Modulation (ESEEM), Magnetic Circular Dichroïsm (MCD) spectroscopy, Mössbauer spectroscopy, resonance Raman spectroscopy, or X‐ray Absorption Spectroscopy. By preparing a series of samples freeze‐quenched after various times, a full kinetic profile of the catalytic cycle of an enzyme or any other chemical reaction is obtained. The structures of intermediates are assigned in conjunction with (a selection of) the spectroscopic techniques listed above.

This article details various aspects of continuous‐flow and stopped‐flow rapid‐mixing techniques, considering mixer design, freeze‐quenching methodology, and sampling. The scope and limitations to (bio)chemical research of the well‐established rapid freeze‐quench (RFQ) and the recently developed microsecond freeze‐hyperquenching (MHQ) technologies are specifically highlighted.
Biologically Templated Nanostructure Assemblies
Authors: Behrens Silke S.
Published: December 2011

Living organisms are able to manufacture a variety of sophisticated inorganic materials with precise control over chemical composition, crystal structure, and shape. Biomolecules offer unique functionalities such as specific recognition capabilities or catalytic activity. On the basis of these recognition capabilities, biological subunits are able to self‐assemble into defined superstructures with unique shapes. Furthermore, they may respond to multiple physical, chemical, or biological stimuli, and therefore provide a potential means for manufacturing nanomachines. However, naturally occurring inorganic materials are typically based on protein scaffolds with inorganic minerals, e.g., iron oxide or calcium carbonate, which limits their technical application. Hence, the knowledge of biological concepts, functions, and design features has recently been exploited for manufacturing new, technologically important, and functional inorganic nanomaterials that have no isomorphous complement in nature.

One major challenge in manufacturing nanostructures by biotemplating has been the need to either modify traditional methodologies derived from chemistry or microelectronics, or to develop new synthetic pathways, in order to make the material synthesis compatible with the relatively labile biotemplates. Various chemical procedures illustrated by selected examples have been elaborated to direct the nucleation and deposition of inorganic materials (e.g., metals, alloys, or semiconductors) on bioassemblies or to link preformed inorganic building blocks to functional biomolecules. Bioassemblies template complex, multidimensional, and inorganic nanoarchitectures that are typically not available by conventional material synthesis. Recently, the templating ability of natural bioassemblies has been improved by means of genetic engineering. Moreover, it has been demonstrated that the biological functionality of the system may be retained under appropriate conditions, which allows the manufacturing of inorganic nanostructures with motility functions. The use of diverse nanostructured bioassemblies based on both proteins (e.g., cell components such as microtubules, microfilaments, S‐layers) or microorganisms (i.e., viruses, diatoms) and deoxyribonucleic acid (DNA) is discussed for their potential of templating of inorganic nanoarchitectures.
Fullerenes: Metal Complexes
Authors: Balch Alan L. , Chancellor Christopher J.
Published: December 2011

This article reviews recent developments regarding the binding of metal centers to the outer surface of fullerenes and to the construction of nanoscale materials utilizing externally bound metal complexes. Developments in the coordination of single metal centers and metal clusters are discussed with particular emphasis placed on crystallographic characterization of the resulting assemblies. Electrochemical work on redox‐active films prepared by reduction of fullerenes and metal complexes is reviewed. The formation of metal containing heterofullerenes—cages of carbon atoms and metal atoms—is examined. Finally, the formation of new crystalline phases by cocrystallization of fullerenes and various metal complexes is examined.
Nano/Microporous Materials: Crystalline Metal‐Chalcogenide Superlattices
Authors: Lin Zhien , Feng Pingyun , Bu Xianhui
Published: December 2011

This article describes the recent research progress in the field of crystalline metal‐chalcogenide superlattices containing tetrahedron‐shaped nanoclusters as building units. With the development of new synthetic strategies and structural concepts, new clusters that are members of three series of tetrahedral clusters (i.e., supertetrahedral clusters, pentasupertetrahedral clusters, and capped supertetrahedral clusters) have been prepared and organized into extended frameworks with a variety of topologies, such as single diamond, double diamond, ABW, CrB4, SOD, cubic C3N4, UCR‐1, ICF‐24, ICF‐25, α‐ and β‐quartz, moganite, and boracite. These materials show rich compositional diversities with tunable optical properties, microporosity, and ion‐exchange properties, suggesting their potential applications in photocatalysis, fast‐ion conductors, solar cells, etc.
Nano/Microporous Materials: Hydrogen‐Storage Materials
Authors: Collins David J. , Zhou Hong‐Cai
Published: December 2011

Both traditional and newly synthesized microporous materials, including activated carbons, carbon nanotubes, zeolites, inorganic nanotubes, and hybrid organic–inorganic materials have been investigated for their ability to adsorb hydrogen. Uptake by these materials is physisorptive, with relatively weak interactions between the material and the hydrogen molecule. Many are able to uptake 1–3 wt% hydrogen at 77 K and 1 atm, and several can adsorb up to 6 wt% under high pressure, but none are currently able to meet hydrogen‐storage goals at near‐ambient temperatures. This review examines the accomplishments, challenges, and future directions in this nascent field.
Nano‐Microporous Materials: Hydrothermal Synthesis of Zeolites
Authors: Valtchev Valentin , Mintova Svetlana
Published: December 2011

This review focuses on the synthesis, crystallization mechanism, and crystal engineering of silica‐based zeolites. The introduction section provides a brief historical overview of zeolite synthesis and points out the main families of microporous solids. The main body of the article comprises two interrelated parts. The first presents basic information related to the zeolite crystallization, namely, (i) the key constituents of a zeolite‐yielding system; (ii) the reactions upon the action of mineralizing agent (OH−and F−); and (iii) the fundamentals of zeolite crystallogenesis. Emphasis is laid on the nucleation process, which is still not well understood. New insights into the zeolite nucleation gained by using colloidal and dense gel systems are discussed. The second part of the survey deals with in situ zeolite crystal engineering. Initially, the synthesis of nanosized particles is considered and then methods for the growth of large, at least 50 µm, zeolite crystals are presented. Further, the control of the crystal morphology via fine tuning of the synthesis variables is discussed. Hybrid zeolites obtained by grafting of organic functionalities during the crystallization reaction are also reviewed. Finally, methods for the synthesis of zeolites with hierarchical porosity are illustrated. This part is subdivided into two sections presenting polycrystalline hierarchical porous structures and single mesopore–containing zeolite crystals.
Periodic Mesoporous Organosilicas
Authors: Yao Baodian , Zhao Dongyuan
Published: December 2011

Periodic mesoporous organosilicas (PMOs) represent a promising new class of organic–inorganic nanocomposite materials in which the organic and inorganic moieties are covalently linked and homogeneously distributed at molecular level. This review retrospected the discovery and development of PMOs in terms of rational synthesis based on the concept of supramolecular self‐assembly. The main focus is on precursors and crystal‐like PMOs. We also highlight the recent achievements regarding compositions and mesostructures, morphologies, and applications in the field. Furthermore, we present an outlook about the promising future perspectives of PMOs that result from the latest developments.
Semiconductor Nanocrystals: Doped Compositions
Authors: Vela Javier , Hollingsworth Jennifer A.
Published: December 2011

We review the state of the art in the field of semiconductor nanocrystal (SC NC) doping, with emphasis on cationic doping for modified optical and magnetic properties. Doping has the potential to greatly expand the already vast technological promise of SC NCs by allowing for the introduction of dopant‐specific or dopant‐modified properties. In the last several years, tremendous progress has been made with respect to both the understanding and implementation of SC NC–doping strategies. Here, we review the prevailing theoretical models (the “dopant extrusion model” and the “sticky surface model”) underpinning the current understanding of the process of dopant ion incorporation during NC growth. Further, we review the general synthetic approaches that have been developed in the context of this understanding, as well as many specific examples of SC NC–dopant systems, revealing both the successes and those that have fallen short in either achieving doping or fully demonstrating that doping was achieved. In support of this aim, we also provide a summary of the characterization methods (spectroscopic, structural, and chemical) that are critical for critiquing the doped system. We have necessarily focused on cationic doping as anionic doping has yet to be realized in a similar fashion. Further, the topic of electronic doping is only briefly addressed. While examples are reasonably abundant with respect to transition metal and lanthanide doping for modified magnetic/optical and optical properties respectively, permanent electronic doping of SC NCs has yet to be demonstrated. Finally, we identify (in addition to anionic and electronic doping) the topic areas that remain to be explored in this field of SC NC doping.
Supramolecular Materials: Metal–Quinonoid Complexes
Authors: Kim Sang Bok , Sweigart Dwight A. , Lotz Simon
Published: December 2011

Simple quinones such as hydroquinone, resorcinol, and catechol can be complexed to a transition metal through the aromatic π‐system. This review focuses on the manganese and rhodium complexes of hydroquinone (H
2
Q), which bind to the metal fragment through all six aromatic carbons (η
6
) to afford (H
2
Q)Mn(CO)
3
+
and (H
2
Q)Rh(COD)
+
. Both of these undergo facile deprotonation to give hydrogen‐bonded semiquinone complexes, which can be deposited on HOPG surfaces. A second deprotonation occurs with concomitant electron transfer to the metal to give anionic η
4
‐benzoquinone complexes that bind to other metals through the quinonoid oxygens. In this way, self‐assembly to metal–organic framework polymer materials results with the (benzoquinone)ML

n

−
moiety serving as the spacer. The resultant polymers are porous and can have tetrahedral, octahedral, and square pyramidal geometries. In the case of rhodium as the metal, the quinonoid complexes are excellent catalysts for carbon–carbon coupling from aryl boronic acids, and activated olefins and aldehydes. The rhodium species also forms self‐supporting coordination networks in the presence of main group alkoxides, and these function as catalysts for acetylene polymerization. The catalysts can also be deposited strongly on silica gel supports. An exciting application of this chemistry is the derivatization of the surfaces of magnetic nanoparticles (MNPs). In the case of superparamagnetic FePt and ferrite nanoparticles (NPs), the quinonoid–metal complexes bind to the surface and function as centers for the growth of coordination polymers. This provides multiple catalytic centers that are subject to magnetic decantation, and constitutes the first generalized methodology for the combination of organometallics with NP surfaces.
Functional Supramolecular Hybrid Materials
Authors: Rurack Knut , Martínez‐Máñez Ramón
Published: December 2011

The combination of suitable nanoscopic inorganic supports with supramolecular concepts and bioconjugation strategies opens up exciting perspectives for the development of bioinorganic and organic–inorganic hybrid materials with improved functionalities. Many of the examples from the period 2004 to mid‐2007 reviewed here bridge the gap between molecules, materials sciences, biochemistry, and nanotechnology. The synergistic use of these approaches has led to the advancement of various functions such as enhanced recognition, amplified signaling, the controlled assembly and disassembly of aggregates and 3‐D architectures. Many of the implemented active functions can be carried out in a reversible and directed fashion on purpose by triggering with an external stimulus. These ideas bring tunability to properties of inorganic solids and new perspectives of application to biochemical and supramolecular concepts. Classic inorganic chemistries such as metal or semiconductor nanoparticles, silica or carbon materials, and coordination chemistry are thus elevated to another level of sophistication and contribute significantly to frontier research areas in directed transport and delivery, nanoelectronics and mechanics, chip technology, smart materials, memory devices, and bioanalytics.
Nano/Microporous Materials: Mesoporous and Surface‐Functionalized Mesoporous Carbon
Authors: Wang Xiqing , Liang Chengdu , Dai Sheng
Published: December 2011

Mesoporous carbon materials, a category of porous carbons with pore size between 2 and 50 nm, have attracted considerable attention owing to their wide applications. There are many conventional methods available for the preparation of mesoporous carbons. Generally, the resulting mesoporous carbon materials have a broad pore size distribution. Carbon materials with uniform pore size can be prepared using porous silica gels or colloidal silica nanoparticles as hard templates. Periodically ordered mesoporous carbons are a recent addition to this category. Ordered mesoporous carbons can be made by a hard template method using ordered mesoporous silicas with three‐dimensionally connected pore structures (e.g., SBA‐15) as the templates. Self‐assembly of thermal decomposable block copolymers with thermosetting resol or novalac resin into mesostructured nanocomposites provides an alternative approach for the synthesis of ordered mesoporous carbons. The carbon materials obtained exhibit high Brunauer–Emett–Teller (BET) surface areas, controllable pore diameters with narrow pore size distribution, and large pore volumes. Efforts aimed toward surface modification of mesoporous carbons that integrate unique mesoporosity with other functionalities have led to many interesting materials and some promising results for applications. With the development of mesoporous and surface‐functionalized mesoporous carbon materials, numerous applications are awaiting the exploration of materials research scientists. Herein we summarize the recent progress in the synthesis and surface modification of mesoporous carbons, mainly on the carbon materials with uniform pore size and/or ordered structures.
Semiconductor/Ceramic Nanocomposites: Synthesis, Characterization, and Properties
Authors: Moore Joshua T.
Published: December 2011

A survey of the preparation of semiconductor nanocrystal‐ceramic nanocomposite materials and related nanostructured materials is provided. Nanocomposite materials described here contain elemental semiconductors (Si and Ge), II–VI and IV–VI semiconductors (ZnE, CdE, and PbE where E = S, Se, Te), and III–V semiconductors (GaE, AlE, and InE where E = N, P, As) embedded in various ceramic matrices. Semiconductor nanocrystals and nanoparticles were prepared using a variety of physical, chemical, and electrochemical synthesis strategies. Sol‐gel processing, and single‐ or multiple‐source precursors were used to prepare semiconductor nanoparticles with diameters as small as 2–4 nm or as large as 50–200 nm. Formation of the semiconductor nanophase was carried out by reduction of mixed‐metal oxides, pyrolysis of well‐characterized precursor molecules or in situ generated precursor complexes, chemical vapor deposition (CVD), and electrochemical reduction.
Semiconductor Nanowires
Authors: Korgel Brian A.
Published: December 2011

This review provides an overview of the synthesis, structural and chemical properties, and assembly and processing strategies of semiconductor nanowires. Vapor–liquid–solid (VLS), solution–liquid–solid (SLS), supercritical fluid–liquid–solid (SFLS) approaches that rely on the formation of a liquid metal–semiconductor eutectic to seed nanowire growth are covered. Nanowire growth from metal seed particles in the solid phase are also discussed, as well as chemical methods that rely on surfactants, self‐assembly, and directed crystallization processes. Structural details about the nanowires, including the crystallographic growth direction, common extended defects, and surface faceting are discussed. Routes to surface passivation by organic monolayers and compositional control of impurity doping and heterostructures—radial and axial—are presented, as well as more structurally complicated branched nanowire structures. Finally, an overview of nanowire processing and manipulation is offered, with a discussion about positioned growth, self‐assembly, and the potential impact of impurities on applications.
Monodisperse Magnetic Nanoparticles: Chemical Synthesis and Surface Modification
Authors: Xie Jin , Sun Shouheng
Published: December 2011

Magnetic nanoparticles, due to their prospective applications in data storage, drug delivery, hyperthermia, and magnetic resonance imaging, have attracted considerable attention in the past decade. From aqueous‐phase condensation to organic‐phase thermal decomposition, the synthesis of magnetic nanoparticles has been greatly improved. Nowadays, one can readily synthesize monodisperse magnetic nanoparticles with controlled sizes, shapes, and magnetic properties. In this article, we first briefly describe the general synthesis of monodisperse nanoparticles, and then focus on the synthesis of magnetic nanoparticles via thermal decomposition of metal precursors. The nanoparticles are grouped into ferrite, metallic, alloy, and multicomponent categories, and the mechanism for the formation of nanoparticles with critical parameters in determining size, shape, and multifunctionality is discussed. We further summarize the chemistry used for nanoparticle surface functionalization and briefly discuss the potential applications of these magnetic nanoparticles in biomedicine.
Inorganic Nanomaterials Synthesis Using Alkalide Reduction
Authors: Wagner Michael J.
Published: December 2011

Chemical (solution) methods of nanomaterial synthesis offer the advantages of simplicity, stoichiometric control, ease of scale‐up, and the possibilities of size control and narrow size distributions. Of the many solution methods of making nanoparticles, the reduction of metal salts by alkalides or electrides, generally referred to asalkalide reduction, is particularly promising due to its ability to protect highly oxyphilic elements and its use of the most power reductants possible in any given solvent. This makes it general across the periodic table including the early transition metals and rare earth elements. In fact, to date, it is the only solution method shown to be capable of synthesizing lanthanide metal nanoparticles. Binary and higher order phase nanomaterials are also possible by the simultaneous alkalide reduction of multiple elements. Nanoscale oxides and nitrides can be formed by reacting nanomaterials made by alkalide reduction with the appropriate gas. Spheroidal nanoparticles as small as ∼1 nm in diameter can be synthesized by this method as can rods up to ∼1 µm in length. The current practice and capabilities of highly versatile synthetic routes to nanomaterials are outlined in this article.
Gold in Homogeneous Catalysis
Authors: Jiménez‐Núñez Eloása , Echavarren Antonio M.
Published: December 2011

The important types of transformations catalyzed by homogeneous Au(I) and Au(III) complexes or salts are reviewed. The reactions are organized mechanistically on the basis of the main functional group being activated by the gold catalyst. Particular emphasis is given on the most general reactions for the formation of CC bonds.