bluuebunny/crossref_metadata_2025_split huggingface dataset:
Semiconductor Nanocrystal Quantum Dots
Authors: Hollingsworth Jennifer A. 
Published: December 2011

AbstractSemiconductor 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

AbstractThe 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

AbstractRecent 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

Abstract
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

Abstract

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

AbstractThe 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

AbstractMeasuring 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

Abstract
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

AbstractOne 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

AbstractX‐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

AbstractElectron‐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

AbstractRapid‐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

AbstractLiving 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

Abstract
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

AbstractThis 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

Abstract
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.