bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐Performance Silicon Nitride Materials
Authors: Boberski Cornelia , Hamminger Rainer , Peuckert Marcell , Aldinger Fritz , Dillinger Reinhard , Heinrich Jürgen , Huber Jürgen
Published: December 2003

The past decade has seen greatly increased interest in ceramic materials with special combinations of properties. Their hardness, high resistance to abrasive and erosive wear, and their good corrosion resistance when used under extreme mechanical and thermal conditions have made ceramics increasingly attractive for applications in mechanical and apparatus engineering. Silicon nitride (Si3N4) in particular, is suitable for the development of a high‐performance, high‐temperature material for vehicle engine construction. Although the properties of Si3N4 materials have been consistently improved in the last few years, they are still not adequate to allow these materials to be used in series production parts, for example as valves in automotive engines. One of the main reasons for this is the wide scatter and low reproducibility of the property parameters, which means that component reliability does not yet meet market requirements. Hence, one aim of Si3N4 materials development is to reduce the structural flaws resulting from physical and chemical inhomogeneity. This objective can only be achieved through a fundamental understanding of all the processing steps, from powder production to the final processing of the components.
Low Temperature Deposition of a CaF2 Insulator Layer on GaAs*
Authors: Vere A. W. , Mackey K. J. , Rodway D. C. , Smith P. C. , Frigo D. M. , Bradley D. C.
Published: December 2003

Research News: Multilayer semiconductor–insulator structures composed of epitaxially grown layers of, for example, GaAs and CaF2 have been the subject of widespread interest in recent years. The methods used to overcome lattice mismatch problems in order to obtain high quality insulator thin films are discussed along with photochemical decomposition methods for their production at low temperatures.
Synthesis, Structure and Reactivity of Sulfur‐Rich Cyclopentadienyl‐Transition Metal Complexes: Sulfur Chemistry from an Organometallic Point of View
Authors: Wachter Joachim
Published: December 2003

Metal‐sulfur centers play an important role in the activity of metalloproteins in enzymatic catalysis and the activity of metal sulfides as heterogeneous catalysts. The systematic search for MS model compounds led to the discovery of an interesting and novel structural chemistry, which stems from the numerous coordination possibilities of sulfur ligands. The intention of this review article is to present and outline new approaches to sulfur chemistry from the organometallic point of view. Reactive cyclopentadienyl‐transition metal fragments incorporate elemental sulfur to give polynuclear sulfur‐rich complexes, which can contain either mono‐, di‐ or polysulfido ligands or several such ligands in combined form. The versatile structural chemistry of the complexes formed and their reactivity towards organic, inorganic and organometallic compounds are discussed, and examples of some simple and rational procedures for their synthesis starting from cyclopentadienylcarbonyl‐ and cyclopentadienylhydrido‐complexes are outlined. Their reactivity is manifested in numerous metal‐ and ligandcentered reactions. Finally the, albeit far less extensive, complex chemistry of the other chalcogens (O, Se, Te) is also considered for comparison, thus providing a more detailed survey of particular aspects of this area of chemistry.
Structural Characterization of Non‐Oxide Chalcogenide Glasses using Solid State NMR
Authors: Eckert Hellmut
Published: December 2003

In spite of the long‐standing importance of non‐oxide chalcogenide glasses in infrared optics and semiconductor technology, concepts describing the structural principles governing glass formation in these systems are just emerging. Most recently, modern quantitative solid state NMR techniques have offered new unique insights into the structural organization of these systems. In this review, we discuss the basic principles of various experimental approaches and their application to boron‐silicon, ‐and phosphorus chalcogenide glasses.
Starburst Dendrimers: Molecular‐Level Control of Size, Shape, Surface Chemistry, Topology, and Flexibility from Atoms to Macroscopic Matter
Authors: Tomalia Donald A. , Naylor Adel M. , Goddard William A.
Published: December 2003

Starburst dendrimers are three‐dimensional, highly ordered oligomeric and polymeric compounds formed by reiterative reaction sequences starting from smaller molecules—“initiator cores” such as ammonia or pentaerythritol. Protecting group strategies are crucial in these syntheses, which proceed via discrete “Aufbau” stages referred to as generations. Critical molecular design parameters (CMDPs) such as size, shape, and surface chemistry may be controlled by the reactions and synthetic building blocks used. Starburst dendrimers can mimic certain properties of micelles and liposomes and even those of biomolecules and the still more complicated, but highly organized, building blocks of biological systems. Numerous applications of these compounds are conceivable, particularly in mimicking the functions of large biomolecules as drug carriers and immunogens. This new branch of “supramolecular chemistry” should spark new developments in both organic and macromolecular chemistry.
The Preparation of Finely Divided Metal and Alloy Powders
Authors: Bönnemann Helmut , Brijoux Werner , Joussen Thomas
Published: December 2003

Finely divided metal and alloy powders can be prepared by reduction or co‐reduction of metal salts in organic solvents. By means of this novel “cold powder technology”, microcrystalline to amorphous metals and alloys are obtained (particle size according to SEM photographs 10–100 nm) which can also be generated on support materials. This is of interest for catalytic applications.
Ketenimine Complexes from Metal Isocyanides and Diazoalkanes
Authors: Strecker Beate , Werner Helmut
Published: December 2003

Free ketenimines can be synthesized in two steps from the readily accessible cobalt isocyanide complexes 1 and diaryldiazoalkanes 2. Thus, ketenimines cannot only be prepared at a metal center from a carbene ligand and an isocyanide but also from an isocyanide ligand and a carbene source, e.g. a diazoalkane. The complexes 3–6 are obtained in 54–68% yield, and the corresponding ketenimines 7–10 can be liberated from these with iodine at room temperature (3/7, 4/8, 5/9: R  Me, CR  CPh2, C(p‐Tol)2, fluorenylides; 6/10: R  CHMePh. CR  fluorenylides).
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Chemiluminescence Techniques for the Characterization of Materials [New Analytical Methods (41)]
Authors: Mendenhall G. David
Published: December 2003

Photons are emitted at low levels from a wide variety of organic materials at wavelengths ranging from the visible to infrared. This light emission accompanies free‐radical autoxidation and charge‐recombination processes and is particulary useful in assessing thermal oxidation and radiation damage as well as polymer curing reactions. IR chemiluminescence, which offers advantages because of reduced self‐absorption, has been shown to mark the end of induction periods in inhibited systems. With the introduction of sensitive solid‐state devices, the chemiluminescence technique has been extended to two‐dimensional imaging and presentation.
Ionic Isomer Distinction by Neutralization‐Reionization Mass Spectrometry (NRMS): Carbonic Acid Radical Cations, (HO)2CO˙⊕ versus (H2O/CO2)˙⊕ Clusters
Authors: Terlouw Johan K. , Sülzle Detlev , Schwarz Helmut
Published: December 2003

Reactions between CO2, and H2O or the corresponding radical cations are easily investigated with the aid of mass spectrometry. Whereas CO2 reacts with H2O to give the weakly bonded van der Waals cluster 1, reaction of H2O.⊕ with CO2 leads exclusively to the proton‐bridged isomer 2.⊕. Attempts with a mass spectrometer to prepare the so far unknown neutral cluster 2 from 2.⊕ under neutralization/reionization conditions were unsuccessful. This is presumably a consequence of the considerable difference between the (calculated) bond lengths and bond angles in the two species 2.⊕ and 2. The formation of (HO)2CO was not observed under these conditions.
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Organometallic Macrocycles: Synthesis and Molecular Structure of Trimeric Tartratodiruthenium Complexes
Authors: Süss‐Fink Georg , Wolfender Jean‐Luc , Neuman Frank , Stoeckli‐Evans Helen
Published: December 2003

A ring containing six Ru atoms, six O atoms, and 12 C atoms occurs in the structure of compound 1, which is characterized by dinuclear metallic units joined through tartrato ligands. 1 is remarkably easy to prepare from Ru3(CO)12 and (R,R)‐, (S,S)‐ or (R,S)‐tartaric acid, with configuration being maintained in the course of the reaction. Observed yields are of the order of 80% The compounds 1 are to be regarded as organometallic macrocycles with chiral structural units.
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Two‐Dimensional Model Networks
Authors: Rehage Heinz , Veyssié Madeleine
Published: December 2003

This article is concerned with the structure and dynamic properties of thin films that have been chemically stabilized by polymerization and cross‐linking reactions. By using different types of monomers it is possible to construct networks with rubber‐like elasticity or with glassy properties, or temporary networks, in the interfacial region between oil and water. The systematic study of these ultrathin membrances offers new insights into aspects of current research, and opens up a wide range of potential new applications.
Stereocontrolled Construction of Complex Cyclic Ketones via Oxy‐Cope Rearrangement
Authors: Paquette Leo A.
Published: December 2003

Convergency is a highly serviceable aspect of organic synthesis, particularly when its application is accompanied by high levels of chirality transfer and regiocontrol. A reaction that is notably well suited to these objectives is the oxy‐Cope rearrangement. In addition, the benefits that can accrue from suitable condensation of β γ‐unsaturated ketones with a vinyl organometallic and subsequent [3,3] sigmatropic shift are substantive enhancement in structural complexity and the ability to generate a myriad of polycyclic frameworks. Another profitable feature is the complementary regeneration of the carbonyl group in a new structural context. In view of the pivotal role played by the carbonyl functionality in synthetic transformations, reacquisition of such a reaction site translates into heightened chemical versatility. The trajectories followed by vinyl organometallics as they engage in 1,2 addition to ketones are gradually being understood. Proper diastereoselective control of this bond‐making process, when coupled with full awareness of the chair or boat topography adopted during the ensuing oxy‐Cope electronic reorganization, provides for exciting new strategy‐level dimensions not often available in other contexts. The use of this two‐step sequence as a prelude to a third chemical event clearly serves to expand the possibilities for molecular construction still more. While a considerable amount of the work to date has focused on the preparation of rather elaborate carbocyclic molecules, principally with a view to gaining access to complex natural products, the possibilities for heterocyclic synthesis are currently being accorded increased attention.
Asymmetric Heterodinuclear [L′Ru(μ‐O)(μ‐CH3CO2)2ML]2⊕ Complexes (M  Fe, Mn, V): Electronic Structure and Magnetic Properties
Authors: Hotzelmann Rainer , Wieghardt Karl , Flörke Ulrich , Haupt Hans‐Jürgen
Published: December 2003

Strong antiferromagnetic coupling or intramolecular electron transfer is found in the products of the reactions of L′RuIIICl3 with LMIIICl3 in aqueous, acetate‐containing solution. Electronic and ESR spectra, susceptibility measurements, as well as the results of X‐ray structure analyses are consistent with the formulation of 1 and 2 as RuIIIMIII complexes with s = 2 and 3/2, respectively, and of 3 as RuIIVIV complex with S = 1/2. L = 1,4,7‐triazacyclononane, L′ = N,N′N″‐trimethyl‐1,4,7‐triazacyclononane.
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The Monofluorooxonium(0) Hexafluorometalate(VI)S H2OF⊕MF (M = As,Sb)
Authors: Minkwitz Rolf , Nowicki Gabriele
Published: December 2003

Oxidative fluorination of H2O with monofluoroxenonium metalates in anhydrous HF [Eq. (a)] afforded access to the monofluorooxonium salts 1, M = As, Sb. The pale red salts can be stored without decomposition for a few weeks at temperatures below 233 K and for up to 2 h at room temperature.
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Base‐Free Cationic 14‐Electron Titanium and Zirconium Alkyls: In situ Generation, Solution Structures, and Olefin Polymerization Activity
Authors: Bochmann Manfred , Jagger Andrew J. , Nicholls Julian C.
Published: December 2003

Multiple insertion of ethylene into the TiCH3 bond, the first direct evidence for the role of cationic intermediates in polymerization reactions, is observed upon reaction of the cationic Ti and Zr complexes 3 at low temperatures. Complexes 3 are formed from 1 and 2 in a reaction involving elimination of methane. Under the same conditions, ethylene in excess undergoes polymerization (M = Ti, Zr).
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Na10{Li2[MnO4]4}, a Compound in Which LiO4 and MnO4 Tetrahedra Form Chains Consisting of Six‐ and Eight‐Membered Rings
Authors: Fischer Dieter , Hoppe Rudolf
Published: December 2003

Annealing thoroughly mixed amounts of the oxides Na2O2 and LiMnO4 (Na:Mn = 2.8:1; Ag bomb, 580°C, 30d) results in formation of Na10 {Li2[MnvO4]4} as blue‐green, orthorhombic crystals. Structure analysis revealed that the MnO4 and LiO4 tetrahedra are linked in a way previously unknown for metal oxides: chain‐shaped anions made up of six‐ and eight‐membered rings are linked through sodium ions.
13C‐MAS‐NMR Spectra of Technical Calcium Carbide and Barium Carbide—Are the C Ions in Ionic Carbides Surrounded Symmetrically?
Authors: Wrackmeyer Bernd , Horchler Klaus , Sebald Angelika , Merwin Lawrence H. , Ross Charles
Published: December 2003

The answer to the question posed by the title is no. Whereas δ(13C) ≈ 140 for a “free” C ion, values of 206.2 and 232.1 are found for the ionic carbides CaC2 and BaC2, respectively, in the solid state. Furthermore, simulation of the 13C MAS NMR spectra shows unambiguously that the C2 units deviate from axial symmetry. For CaC2, the presence of a second phase, identified from X‐ray powder patterns, was confirmed by NMR spectroscopy.
Complexes of Carbon Monoxide and Its Relatives: An Organometallic Family Celebrates Its Birthday
Authors: Werner Helmut
Published: December 2003

Nickel tetracarbonyl was discovered one hundred years ago. Its hundredth birthday deserves to be celebrated not only by metal carbonyl chemists. The pioneering work of Mond, Langer, and Quincke has led to developments which, particularly in the last 30 years, have had consequences in many areas outside that of metal carbonyl chemistry. The parent ligand of the family, CO, has been joined by a series of relatives which are isoelectronic with it and which in some cases are even more effective as π acceptors. These are in the main extremely reactive molecules such as CS, CNH, and C= CH2, which, though very short‐lived in the free state, form very stable complexes with transition metals. This article documents the family relationships by structure and reactivity comparisons; attention is also drawn to the synthetic potential of the metal carbonyl analogues, which is still virtually untapped. The final section ventures a look towards the next 100 years, which promise to be just as exciting as the past century.
Electrostatic Control of the Molecular and Crystal Structure of an Olefinic Double Betaine
Authors: Weiss Robert , Roth Reinhardt , Lowack Rainer H. , Bremer Matthias
Published: December 2003

No Absract.
[(Ph3P)2N]2[Os18Hg2C2(CO)42] a Photochemically Generated High‐Nuclearity Cluster Which Reversibly Incorporates Metallic Mercury into Its Metal Core
Authors: Charalambous Eleni , Gade Lutz H. , Johnson Brian F. G. , Kotch Thomas , Lees Alistair J. , Lewis Jack , McPartlin Mary
Published: December 2003

No Absract.
Selective Deamidation of Peptide Amides
Authors: Steinke Dörte , Kula Maria‐Regina
Published: December 2003

No Absract.
2,3,4,5‐Tetramethyl‐1‐sodiopyrrole: An Azacyclopentadienyl Ligand in a Novel Bridging Function
Authors: Kuhn Norbert , Henkel Gerald , Kreutzberg Jörg
Published: December 2003

No Absract.
A Novel Palladium‐Catalyzed Carbonylation of Aromatic N‐Chlorosulfonamidates to Arylsulfonyl Isocyanates
Authors: Besenyei Gábor , Németh Sándor , Simándi Lászlò I.
Published: December 2003

No Absract.
Stable Azirinimines? A Structural Corrigendum
Authors: Banert Klaus , Reissaus Elisabeth , Deiseroth Hans‐Jörg , Kluge Claus Peter , Peters Eva‐Maria
Published: December 2003

No Absract.
Misconceptions on Pollution and the Causes of Cancer
Authors: Ames Bruce N. , Gold Lois Swirsky
Published: December 2003

The public has numerous misconceptions about the relationship between environmental pollution and human cancer. Underlying these misconceptions is an erroneous belief that nature is benign. In this article we highlight eight of these misconceptions and describe the scientific information that undermines each one.
What Does the Chemical Industry Expect from Physical and Industrial Chemistry?
Authors: Jentzsch Wolfgang
Published: December 2003

Process innovation—the systematic optimization of raw materials, energy consumption and product yields—is a constant challenge for those operating plants producing vital basic and intermediate chemicals. The production processes, rather than the products themselves, exhibit life cycles and determine the profitability of downstream manufacturing. The ongoing task of interdisciplinary teams of experts is not just to develop new process routes, but, more commonly, to improve individual process steps. The impulse for this innovation arises from changes in the price and availability of raw materials, economic and environmental considerations and, last but not least, scientific and technological progress. This paper illustrates the opportunities available using examples which have already been put into practice as well as problems not yet resolved. Questions such as the use of alternative feedstocks and the switch to catalytic processes arc addressed and used to suggest novel ideals for basic research. Worthwhile projects are identified in the area of industrial oxidation, both catalytic and non‐catalytic. A highly developed, systematic, computer‐based method for optimizing the integration of energy flows within a plant is presented and novel measurement techniques for efficient production control and product quality are. discussed. The successful realization of such concepts requires the ability and the willingness to think in terms of new approaches to problem solving, making this an important objective for university education geared to future needs.
Specific Interactions of Proteins with Functional Lipid Monolayers—Ways of Simulating Biomembrane Processes
Authors: Ahlers Michael , Müller Wolfgang , Reichert Anke , Ringsdorf Helmut , Venzmer Joachim
Published: December 2003

The interplay between molecular self‐organization and molecular recognition leads to the construction of functional supramolecular systems in which order and mobility are combined and whose function is based on their organization. These fascinating phenomena, for which the living cell is a perfect example, can be understood only if a wide range of scientific disciplines work together. For this purpose, synthetic supramolecular systems can be used to simulate natural biomembrane processes. One example of this is the specific recognition and interaction between membrane‐bound ligands and receptor proteins. Thus, the specific interaction of vitamin H (biotin) with the tetrafunctional protein streptavidin in the monolayer leads to 2D crystallization of the protein. Structural analysis shows that the protein is attached to the lipid membrane by two biotin‐binding sites, leaving two still free. The opportunity this allows for biotinylated molecules to dock to the protein leads to interesting possibilities for constructing protein‐containing functional multilayers. Another example for the simulation of biomembrane processes is the function of enzymes which is coupled to the recognition process. In the interaction of phospholipase A2 with lecithin monolayers, specific recognition between enzyme and substrate is followed by an active phase of lipid cleavage and then by aggregation of the enzyme to give domains of regular morphology. Fluorescence microscopy can be used to follow this process directly: an enzyme caught in action. Der Witz ist der Finder und der Verstand der Beobachter. Georg Christoph Lichtenberg

“Wit is the finder and intelligence the observer” [1a].
Synthesis and Structure of [Et2OZn(SC6H2tBu3)2], the First T‐Shaped Zinc Complex
Authors: Power Philip P. , Shoner Steven C.
Published: December 2003

The stacking of aryl groups once again appears to be structure‐determining. The title complex, which is accessible by reaction of [Zn(CH2SiMe3)2] with two equivalents of 2,4,6‐tBuC6H2SH in the presence of Et2O, has an SZnS angle of ca. 160° and ZnS distances of only 2.196 Å. In contrast, the ZnO distance is relatively large and explains the ready cleavability of the ether ligands. Zinc thiolates are of interest as model complexes for zinc‐containing proteins.
Thermodynamic Aldehyde Enantioface Binding Selectivities in Complexes of Chiral Metal Fragments; Mechanism of Interconversion of Diastereomeric π‐Aldehyde Complexes [(η5‐C5H5)Re(NO)(PPh3)(η2‐OCHAr)]BF4
Authors: Méndez N. Quirós , Mayne Charles L. , Gladysz J. A.
Published: December 2003

The higher the π‐acidity of the aldehyde ligand the more pronounced the chiral recognition in its bonding to the chiral complex 1. This emerges from low‐temperature NMR spectroscopic investigations on reactions of the complex 1 with the aromatic aldehydes 2, which, in addition, showed that the diastereomeric π‐aldehyde complexes of 1 and 2 interconvert intramolecularly via a σ‐aldehyde complex.
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Polyoxometalate Chemistry: An Old Field with New Dimensions in Several Disciplines
Authors: Pope Michael T. , Müller Achim
Published: December 2003

Inorganic metal–oxygen cluster anions form a class of compounds that is unique in its topological and electronic versatility and is important in several disciplines. Names such as Berzelius, Werner, and Pauling appear in the early literature of the field. These clusters (so‐called isopoly‐ and heteropolyanions) contain highly symmetrical core assemblies of MOx units (M = V, Mo, W) and often adopt quasi‐spherical structures based on Archimedean and Platonic solids of considerable topological interest. Understanding the driving force for the formation of high‐nuclearity clusters is still a formidable challenge. Polyoxoanions are important models for elucidating the biological and catalytic action of metal–chalcogenide clusters, since metal–metal interactions in the oxo clusters range from very weak (virtually none) to strong (metal–metal bonding) and can be controlled by choice of metal (3d, 4d, 5d), electron population (degree of reduction), and extent of protonation. Mixed‐valence vanadates, in particular, show novel capacities for unpaired electrons, and the magnetic properties of these complexes may be tuned in a stepwise manner. Many vanadates also act as cryptands and clathrate hosts not only for neutral molecules and cations but also for anions, whereby a remarkable “induced self‐assembly process” often occurs. Polyoxometalates have found applications in analytical and clinical chemistry, catalysis (including photocatalysis), biochemistry (electron transport inhibition), medicine (antitumoral, antiviral, and even anti‐HIV activity), and solid‐state devices. These fields are the focus of much current research. Metal–oxygen clusters are also present in the geosphere and possibly in the biosphere. The mixed–valence vanadates contribute to an understanding of the extremely versatile geochemistry of the metal. The significant differences between the chemistry of the polyoxoanions and that of the thioanions of the same elements is of relevance to heterogeneous catalysis, bioinorganic chemistry, and veterinary medicine.
Pulsed Electron Spin Resonance Spectroscopy: Basic Principles, Techniques, and Examples of Applications [New Analytical Methods (43)]
Authors: Schweiger Arthur
Published: December 2003

Electron spin resonance (ESR) Spectroscopy has recently undergone a major innovative advance, which is described by the magical phrase pulsed ESR. To the spectroscopist who rubs this Aladdin's lamp there now opens up the mysterious world of spin acrobatics with its many novel and surprising phenomena. The use of pulse techniques makes it possible to reduce measurement times, increase sensitivity, improve resolution and simplify spectra. This article describes the most important pulse techniques used in ESR spectroscopy. Mathematical descriptions are kept to a minimum, space being devoted instead to examples of applications in various areas of chemical research.
Monovalency of the Third Main‐Group Elements: News from EX‐Type Compounds
Authors: Paetzold Peter
Published: December 2003

Boranediyls, alanediyls, and gallanediyls, :EX, are enfants terribles because of their unorthodox reactivity and structural diversity. For this very reason, however, their chemistry is more promising than that of the analogous species :E'X2 of the fourth main group. H. Schnöckel et al. have made an important contribution to the chemistry of these monovalent substances by synthesizing and structurally characterizing the cluster [{Al(C6Me5)}4] (see page 564).
Blocking of Acidic Centers upon Hydrothermal Dealumination of ZSM‐5 Zeolites
Authors: Richter Manfred
Published: December 2003

The effect of insoluble extralattice aluminum species on material transport is presumably the reason for the changes in activity and selectivity observed for m‐xylene isomerization on dealuminated ZSM‐5 catalysts. This conclusion resulted from determinations of catalytic activity for a related test reaction, the rearrangement of ethylbenzene. Thus, the oft‐repeated suggestion that a modification of the activity is due to a blocking or freeing of acidic centers in the zeolite is invalid.
Synthesis and Characterization of P‐containing ZSM‐5 Zeolites
Authors: Reschetilowski Wladimir , Meier Brit , Hunger Michael , Unger Baldur , Wendlandt Klaus‐Peter
Published: December 2003

The hydrothermal crystallization of a mixture of water glass and aluminum sulfate after addition of phosphoric acid and n‐propylamine enables the preparation of ZSM‐5 zeolites with variable P content. When the P content is increased the distribution of acid strength of the acidic OH groups is shifted in favor of the weakly acidic Brønsted acidic centers. This is of fundamental importance for the preparation of tailor‐made catalysts for proton‐catalyzed reactions.
Bonding Patterns in Intermetallic Compounds
Authors: Nesper Reinhard
Published: December 2003

Intermetallic phases have long been among the black sheep in the family of chemical compounds. Their chemical bonding has eluded description by the valence rules, which otherwise are extremely effective. As a result, understanding of the structure–bonding relationships in these phases to date has remained nebulous, even though they form the largest group of inorganic compounds. Their broad industrial applicability and richly varied structural chemistry call for new approaches for explaining their structures, electronic structures, and physical properties. A combination of new experimental and theoretical investigations has revealed interesting local aspects of chemical bonding in metals and thereby pointed to a route from the valence compounds, through the cluster and electron‐deficient compounds, to the intermetallic phases.
Between Stars and Metals: Phosphorus Monoxide, PO
Authors: Herrmann Wolfgang A.
Published: December 2003

The search for “heavy brothers”, the homologues of the ubiquitous CO and NO ligands in organometallic chemistry, presses ahead and not without success. Although the stabilization of SiO by a metal complex is still not possible, O. J. Scherer et al. achieved the breakthrough by synthesizing a complex containing PO, [(Cp′Ni)2W(CO)4(PO)2] (Cp′ = η5‐C5iPr4H). (See also the communication on p. 852). Seen in the context of the other homologues, this development promises to be the forerunner of many such exciting possibilities.
On the Electrochemical Oxidation of Cs⊕ and Other Alkali‐Metal Ions in Liquid Sulfur Dioxide and Acetonitrile
Authors: Jehoulet Christophe , Bard Allen J.
Published: December 2003

The electrochemical oxidation of the alkali‐metal ions Cs⊕, Rb⊕, K⊕, and Na⊕ appears to occur in liquid sulfur dioxide, but only at about + 4.7 V vs. SCE, as shown by studies on their AsF and PF salts for which other sources of the observed oxidation waves could be excluded. No evidence for the oxidation, previously reported by Seppelt et al., of Cs⊕ in acetonitrile at less positive potentials could be found. It is astounding that all four alkali‐metal ions studied are oxidized at the same potential.
LiClO4 in Ether—an Unusual Solvent
Authors: Waldmann Herbert
Published: December 2003

Ionic reactions with polarized transition states are favored by the solvent system LiClO4/Et2O (3–5M). This is demonstrated by (hetero) Diels–Alder reactions and by the sigmatropic rearrangement of ally1 vinyl ethers in this medium. The former react even faster and with higher endo selectivity than in water; the latter are not [3,3] but [1,3] sigmatropic rearrangements, which yield aldehydes. An important advantage of the LiClO4/Et2O system is it that may also be used for acceleration of reactions sensitive to hydrolysis.
Laser Flash Photolysis Generation, Spectra, and Lifetimes of Phenylcarbenium Ions in Trifluoroethanol and Hexafluoroisopropyl Alcohol. On the UV Spectrum of the Benzyl Cation
Authors: McClelland Robert A. , Chan Christopher , Cozens Frances , Modro Agnieszka , Steenken Steen
Published: December 2003

What UV/VIS properties are anticipated for the benzyl cation? Studies on substituted benzyl cations created by laser flash photolysis predict a strong band at λ = 300–310 nm and a (ca. 90%) weaker band at λ = 430–460 nm for PhCH2. This indicates that the transient formed by pulse radiolysis and described in the literature as a benzyl cation with λmax = 363 nm is probably another carbenium ion, perhaps a cyclohexadienyl cation. The lifetime for PhCh in (CF3)2CHOH is probably only 2–20 ns.
Chemistry and Biology of the Enediyne Anticancer Antibiotics
Authors: Nicolaou K. C. , Dai W.‐M.
Published: December 2003

Novel, biologically active substances from nature often provide excitement, stimulation, challenges, and opportunities for the scientific and medical communities. Experience and wisdom dictate investigation of their chemistry and pursuit of their chemical synthesis for more often than not, the rewards for both chemistry and medicine are great. The enediyne anticancer antibiotics are a rapidly emerging class of such compounds derived from bacterial sources. Combining unprecedented and highly unusual molecular architecture, phenomenal biological activities and fascinating modes of action, these DNA cleaving compounds burst onto the scene in the latter half of the 1980s when their structures became known, and they rapidly moved to center stage. Today the enediyne family includes the neocarzinostatin chromophore, the calicheamicins, the esperamicins, and the dynemicins, and soon the number of family members is certain to increase. These molecules elicited extensive research activities in chemical, biological, and biomedical circles and inspired the design of a number of novel molecular assemblies to probe and mimic their chemical and biological actions. A new body of synthetic technology and several novel synthetic strategies have already been devised to address the challenges posed by these molecules, and several new DNA cleaving agents have been designed and synthesized. This article summarizes the chemistry and biology of the enediynes and discusses mechanistic, synthetic, molecular design, and DNA cleavage aspects associated with the field.
[FCNF]+[AsF6]−, a Salt of the Linear 22‐Valence Electron Cation [FCNF]+
Authors: Tornieporth‐Oetting Inis C. , Gowik Petra , Klapötke Thomas M.
Published: December 2003

Fluorination of the [HCNH]+ ion of 1 in hydrogen fluoride produces the 30‐electron cation [FCNF]+ of 2. According to 19F NMR and vibrational spectra this ion has a linear structure, which is in agreement with the predictions made by ab initio calculations.
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New Forms and Functions of Tellurium: From Polycations to Metal Halide Tellurides
Authors: Beck Johannes
Published: December 2003

Metal chalcogenides and metal chalcogenide halides are distinguished by their structural diversity and by their very different physical properties. Therefore, the synthesis of novel compounds from this class is always a rewarding goal for the preparatively oriented solid‐state chemist. Over the past few years, many syntheses and structural investigations have stimulated the field. The emphasis of the research has been placed on selenium‐rich and tellurium‐rich compounds, which are characterized by directed covalent bonds between the chalcogen atoms. Compounds with novel chalcogen polycations have also become accessible during the past few years by reacting the chalcogen elements with transition metal halides, or from chemical vapor deposition in the sense of chemical transport reactions. In these compounds, tellurium differs from its lighter homologues by a pronounced tendency towards greater covalence. This article attmepts to provide an overview of new developments in the field of compounds with chalcogen polycations and of metal chalcogenide halides, with an emphasis on compounds containing molybdenum and tungsten as the transition metals and tellurium as the chalcogen.
Protein Structure Determination with Three‐ and Four‐Dimensional NMR Spectroscopy
Authors: Oschkinat Hartmut , Müller Thomas , Dieckmann Thorsten
Published: December 2003

Structural biology has made important contributions to the understanding of biological processes. In recent years an increasing amount of structural information has also been derived from NMR spectroscopic studies, often with special emphasis on dynamic aspects. The introduction of three‐ and four‐dimensional techniques has greatly simplified protein structure determination by NMR Spectroscopy, which has in fact become routine. In the past it was more of an art to interpret the complicated NOESY spectra of proteins, but the application of three‐dimensional techniques now makes the interpretation of protein spectra straightforward.

In this review we discuss the most important multidimensional NMR techniques along with suitable applications. The emphasis is put less on the discussion of individual pulse sequences than on their application to the structure determination of proteins.
Reply
Authors: Schlögl Robert
Published: December 2003

“Catalysis research is not black magic!” maintain proponents of rational design in catalysis research, in response to the assertion made by R. Schlögl (Angew. Chem. Int. Ed. Chem. 1993, 32, 381–383) that the development of practical catalysts is still dependent on empirical facts. A number of industrial processes that depend on finely tuned catalysts are cited in support of their premise. In his reply Schlögl restates his thesis and encourages the productive cooperation of “scientific” and “intuitive” approaches to catalyst design.
Template Syntheses
Authors: Hoss Ralf , Vögtle Fritz
Published: December 2003

Although the principle of template synthesis has been known since the sixties, surprising discoveries and new applications in the field of supramolecular chemistry over the last decade have provoked a boom in the subject. The synthesis of supramolecular species has been made much more efficient, or even in some cases possible, by the introduction of template ions or molecules. It is not just metal ions that can act as templates. Neutral molecules, electrostatic interactions, and hydrogen bonds also support the formation of binary and tertiary complexes. Energetically favorable conformations then lead to the formation of a specific desired product in high yield. In addition to the discussion of metal ions and neutral molecules as templates, covalent, positive, and negative templates are differentiated. Kinetic and thermodynamic aspects will also be considered in this review, together with the influence of templates on the phenomenon of self‐organization. Further developments and applications include the synthesis of oligonucleotides, peptide blocks capable of forming secondary structure, and template polymers. Template synthesis of defined molecular cavities ultimately leads to “inclusion chemistry on a nanometer scale.”
Cyclosporin: A Li‐ and Ca‐Specific Ionophore!
Authors: Bürger H. Michael , Seebach Dieter
Published: December 2003

The ionophoric properties of cyclosporin shed new light on its role in immunosuppresion: Cyclosporin transports Li+ and Ca2+ significantly faster than appropriate for their position in the series of alkali metal and alkaline‐earth metal ions, respectively. The migration of the picrates of these metals through a CH2Cl2 solution of cyclosporin (which functions as a liquid membrane) has been examined.
Structural Principles in Seven‐Coordinate Subgroup Compounds: The Complex Anions MoF, WF, and ReOF
Authors: Giese Steffi , Seppelt Konrad
Published: December 2003

Which coordination polyhedron occurs for compounds with coordination number seven? For d0 subgroup compounds the principle of the highest possible symmetry holds; in other words, capped octahedra result for complexes with seven identical ligands and when the interionic forces can be neglected. This is in sharp contrast to the analogous main group compounds, which form pentagonal bipyramids. When subgroup compounds contain one larger ligand and six smaller ones, pentagonalbipyramidal structures occur.
Molecular Solids as Ligands in Organometallic Chemistry: [CpTi6Na7F19·2.5thf] (Cp*  C5Me5) and [CpTi4Mg2F12·7thf], Links Between Ionic Solids and Organometallic Compounds
Authors: Liu Feng‐Quan , Kuhn Annja , Herbst‐Irmer Regine , Stalke Dietmar , Roesky Herbert W.
Published: December 2003

Central NaF and MgF2 frameworks are present in the title compounds obtained from the reaction of [Cp*TiF3] (Cp  C5Me5) with elemental sodium and magnesium, respectively. In these reactions TiIV is reduced to TiIII. The Cp*Ti units function as organometallics shields around the cagelike core and are responsible for the high solubility of the compounds.
The Equilibrium Distribution of Semivolatile Organochloro Compounds between Atmosphere and Surface Water in the Atlantic Ocean
Authors: Schreitmüller Jörn , Ballschmiter Karlheinz
Published: December 2003

The South Atlantic Ocean is of global importance as sink and source for anthropogenic pollutants. Here the distribution of polychlorinated cyclic hydrocarbons between surface water and the atmosphere in this region is shown to fit a classical thermodynamic model of a temperature‐dependent equilibrium—a new example of the concept of a global environmental chemistry.
Discrete M6N Octahedra in the Subnitrides Na16 Ba6N and Ag16Ca6N: A Reconsideration of the Ag8Ca3 Structure Type
Authors: Snyder G. Jeffrey , Simon Arndt
Published: December 2003

The future of subnitride chemistry appears promising: M6 octahedra with a central N atom have been detected in the new compound Na16Ba6N and in the compound hitherto described as “Ag8Ca3”; the latter is actually the isotypic Ag16Ca6N (with 0.7% N)! In these compounds the M6N octahedra are embedded in a matrix of Na and Ag, respectively. Numerous phases with the Ag8Ca3 structure such as Ni6Si2M3 and Ni6Al2M3 (M = rare‐earth metal) may likewise be stabilized by interstitial atoms.
Stereocontrolled Synthesis of Oligo(nucleoside phosphorothioate)s
Authors: Stec Wojciech J. , Wilk Andrzej
Published: December 2003

Encouraging results obtained for modulation of gene expression by antisense oligonucleotides and their analogues have kindled hopes for a new generation of therapeutics against viral infections, cancer, and many other diseases. Among such analogues, oligo(nucleoside phosphorothioate)s (Oligo‐S) have generally shown the highest efficacy in inhibiting the biosynthesis of “unwanted” proteins. The first clinical trials of antisense agents are now in progress using Oligo‐S against genital warts and acute myeloid leukemia, and tests of Oligo‐S against AIDS should follow soon. Nevertheless, their mechanism of action, internalization, cellular trafficking, subcellular localization, and interaction with cellular proteins is still poorly understood. It is assumed a priori that application involves rapid and efficient molecular recognition of target RNA by Oligo‐S; however, the effects of the chirality of Oligo‐S have so far been unappreciated, because Oligo‐S has not yet been synthesized with stereocontrol. Indeed, the diastereomeric composition of Oligo‐S has never been determined, primarily because of the lack of appropriate analytical methods. Since each of the diastereomers is a stereochemically unique chemical entity, questions arise as to which diastereomer is responsible for an observed biological response, including positive (curative) or possibly negative (toxic) side effects.

In this review we intend provide a perhaps somewhat speculative assessment of the problems associated with the stereo‐controlled synthesis of Oligo‐S and to discuss the state‐of‐the‐art in this field including strategies that may lead to Oligo‐S of predetermined chirality. This article is not intended to discourage researchers from further studies of dia‐steromeric mixtures of Oligo‐S as potential pharmaceuticals. Throughout the history of medicinal chemistry numerous useful medicines were discovered, developed, and employed without the detailed knowledge of their structure. Indeed, the composition of the vaccines discovered by Pasteur is a subject of vigorous study still today.
Ladder Sequencing of Peptides and Proteins—A Combination of Edman Degradation and Mass Spectrometry
Authors: Metzger Jörg W.
Published: December 2003

Readout of an entire protein sequence from a mass spectrum, a high sample throughput, and the possibility of sequencing modified peptides or peptides containing unusual amino acids are the advantages of the combination of Edman degradation and mass spectrometry (MS). Fully automated sequencers based on this ladder sequencing technique would provide viable alternatives to the standard sequencers equipped with on‐line HPLC. This technique shows the potential of novel ionization and MS techniques for future protein analysis.
Determination of the Relative Configuration by Distance Geometry Calculations with Proton–Proton Distances from NOESY Spectra
Authors: Reggelin Michael , Köck Matthias , Conde‐Frieboes Kilian , Mierke Dale
Published: December 2003

The determination of the structures of molecules in solution is a challenge. Now the relative configuration, and to a certain extent, the preferred conformation of a flexible chiral compound can be determined by calculations employing data obtained from NMR cross‐relaxation experiments. Force field parameters and conformational preferences need not be specified.
Cyclodextrins as Building Blocks for Supramolecular Structures and Functional Units
Authors: Wenz Gerhard
Published: December 2003

Cyclodextrins are frequently used as building blocks, because they can be linked both covalently and noncovalently with specificity. Thus one, two, three, seven, fourteen, eighteen, or twenty substituents have been linked to one β‐cyclodextrin molecule in a regioselective manner. Furthermore, Cyclodextrins may serve as organic host molecules. Their internal cavity is able to accommodate one or two guest molecules. Conversely, suitable guest molecules can be used to thread one, two, or many (one hundred or more) cyclodextrin rings. The resulting supramolecular structures are often formed in solution, which allows characterization by high‐resolution spectroscopic methods. Chemical conversion of these structures provides molecular architectures such as catenanes, rotaxanes, polyrotaxanes, and tubes, which are not readily prepared by other methods. The particular properties of Cyclodextrins can also be employed, for example, for the chromatographic separation of complex mixtures of substances, even racemates, by molecular recognition. Cyclodextrins and their derivatives have been found to be remarkably active catalysts as well. Finally, since Cyclodextrins can favorably influence the release of drugs, many new applications will certainly be developed in the near future.
X‐Ray Structure Analysis of Methane Monooxygenase: An Important Step toward Understanding the Oxidation of Methane in Biological Systems
Authors: Krebs Bernt , Sträter Norbert
Published: December 2003

Immense ecological and technical importance is enjoyed by methanotrophic bacteria, which can oxidize hydrocarbons to CO2. The key to understanding the mode of action of the enzyme methane monooxygenase is held by the research groups of S. J. Lippard and P. Nordlund, who unraveled the structure of the active site. The processes in the oxidation of methane by air to form methanol under physiological conditions [Eq. (a)] will perhaps soon be elucidated on a molecular level.
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Fullercages without Carbon—Fulleranes, Fullerenes, Space‐filler‐enes?
Authors: Nesper Reinhard
Published: December 2003

Fullerene‐type structures in other areas of chemistry? Fullercages are elements in feasible structure descriptions of a series of intermetallic phases. In contrast to the carbon fullerenes, single bonds are proposed in these systems, and rather than isolated cages, endohedral polyhedra and covalently bound adjacent cages are found. As an example, Na96In97Z2, Z = Ni, Pd, Pt, can be described as containing Z@In10@Na39@In74.
Scales of Nucleophilicity and Electrophilicity: A System for Ordering Polar Organic and Organometallic Reactions
Authors: Mayr Herbert , Patz Matthias
Published: December 2003

Contrary to widely held opinion, for many reactions in organic and organometallic chemistry it is possible to define nucleophilicity and electrophilicity parameters that are independent of the reaction partners. This phenomenon, discovered by Ritchie during the early 1970s for reactions of highly stabilized carbenium and diazonium ions with n‐nucleophiles, also occurs with reactions of carbenium ions with aliphatic and aromatic π‐electron systems and in hydride transfer reactions. With the aid of the scales of nucleophilicity and electrophilicity set out here, which extend over eighteen orders of magnitude, forecasts can be made about the feasibility and rate of a given CC bond formation, ionic reduction, or diazo coupling. Linkage with the reactivity scales of Ritchie and Sweigart/Kane‐Maguire enables a unified treatment of a large number of polar reactions.
Methylbismuth(V) Compounds
Authors: Wallenhauer Stephan , Seppelt Konrad
Published: December 2003

One alkylbismuth(V) compound stable up to 150 °C and three other unstable ones were prepared and structurally characterized for the first time, namely, BiMe CF3SO (the stable species), BiMe3Cl2, BiMe5, and [Li(thf)4]+ BiMe. The tetramethyl compound, the hexamethyl compound, and the dichloride are, as expected, tetrahedral, octahedral, and trigonal bipyramidal, respectively. However, based on the blue‐violet color, a square pyramid was expected for BiMe5, and not the observed trigonal bipyramid.
Composition of Protocyanin, A Self‐Assembled Supramolecular Pigment from the Blue Cornflower, Centaurea cyanus
Authors: Kondo Tadao , Ueda Minoru , Tamura Hirotoshi , Yoshida Kumi , Isobe Minoru , Goto Toshio
Published: December 2003

Reconstruction, not decomposition, was used to determine the composition of the pigment from the blue petals of cornflowers, protocyanin. Comparison of optical and mass spectra of natural and reconstructed protocyanin revealed it to be a complex of an anthocyanin and a malonylflavone with iron(III) and magnesium ions.