J. Appl. Cryst.の発刊に際して

The program Mercury, developed by the Cambridge Crystallographic Data Centre, is designed primarily as a crystal structure visualization tool. A new module of functionality has been produced, called the Materials Module, which allows highly customizable searching of structural databases for intermolecular interaction motifs and packing patterns. This new module also includes the ability to perform packing similarity calculations between structures containing the same compound. In addition to the Materials Module, a range of further enhancements to Mercury has been added in this latest release, including void visualization and links to ConQuest, Mogul and IsoStar.

Mercury CSD 2.0 – new features for the visualization and investigation of crystal structures

3.2.3. Hydroformylation 2467 3.2.4. Dimerization 2468 3.2.5. Oxidative Cleavage and Ozonolysis 2469 3.2.6. Metathesis 2470 4. Terpenes 2472 4.1. Pinene 2472 4.1.1. Isomerization: R-Pinene 2472 4.1.2. Epoxidation of R-Pinene 2475 4.1.3. Isomerization of R-Pinene Oxide 2477 4.1.4. Hydration of R-Pinene: R-Terpineol 2478 4.1.5. Dehydroisomerization 2479 4.2. Limonene 2480 4.2.1. Isomerization 2480 4.2.2. Epoxidation: Limonene Oxide 2480 4.2.3. Isomerization of Limonene Oxide 2481 4.2.4. Dehydroisomerization of Limonene and Terpenes To Produce Cymene 2481

Chemical Routes for the Transformation of Biomass into Chemicals

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

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Chemical Redox Agents for Organometallic Chemistry

The interplay of coordinative, hydrogen bonding and π–π stacking interactions in sustaining supramolecular solid-state architectures.

Hetero- and Metallasiloxanes Derived from Silanediols, Disilanols, Silanetriols, and Trisilanols

The chemistry of silicon is mainly based on silicon(IV), whereas that of silicon(II) is still in its infancy. Silylene (R2Si:) is a molecule with a divalent neutral silicon atom having a lone pair of electrons. Silylenes are key intermediates in various photochemical, thermal, and metal reduction reactions of organosilicon compounds. Therefore, silylenes play a vital role in the field of silicon chemistry. Until 1994, silylenes were generally considered to be very reactive unstable species that decompose or polymerize readily at temperatures above 77 K. This situation changed when West et al. reported the first N-heterocyclic silylene that is stable at room temperature. Since then, a fair number of cyclic silylenes and a dialkyl silylene have been reported. Only one example of a monochlorosilylene that is stable at room temperature has been published, and it was characterized by X-ray diffraction; no dihalosilylenes that are stable at room temperature have been reported to date. Gaseous dichlorosilylene has been known for many years; at room temperature, it condenses to polymeric (SiCl2)n. Its properties were already studied by Schmeisser and Schenk in 1964. Some reactions of condensed SiCl2 with acetylene and with benzene were carried out by Timms in 1968, and resulted in brown polymeric products of unknown composition. A literature survey reveals that there have been few reports on the synthesis and properties of cyclic and linear polydichlorosilanes. A polymeric perchloropolysilane (SiCl2)n was reported by West et al. in 1998 and was studied by single crystal Xray diffraction. However, access to dichlorosilylenes that are stable at room temperature and with electronic structure and properties are quite similar or close to those of unstable examples, such as SiCl2, is still a challenge. Of course, efforts of making a stable version of a very reactive species may cause a change of its behavior. How an unstable species can be stabilized is a matter of keen interest for the scientific and industrial community. Addition reactions of HSiCl3 with different organic compounds in the presence of various tertiary amine bases were reviewed by Benkeser, and the existence of the trichlorosilyl anion as an intermediate was postulated. Moreover, Jung et al. reported the trapping of dichlorosilylene, which was generated by the reaction of HSiCl3 in the presence of phosphonium chloride in a stainless steel cylinder at 150 or 180 8C, by conjugated dienes and by an alkyne. In their proposed mechanism, species of dichlorosilylene or the trichlorosilyl anion as intermediates were discussed but not isolated. In 1995, Kuhn et al. prepared N-heterocyclic carbene (NHC) adducts of SiCl4. We have used N-heterocyclic carbenes as dehydrochlorinating agents for the preparation of germylene and metal hydroxides. Very recently, Robinson and co-workers reported a Lewis base stabilized low-valent silicon compound in which the silicon atom is present in the formal oxidation states + 1 or zero, but no dichlorosilylene was isolated. Almost all silylenes or low-valent silicon compounds reported to date were prepared by reductions of their parent compounds using strong reducing agents, such as potassium metal or KC8. Herein, we report the synthesis of the first basestabilized dichlorosilylene that is stable at room temperature, LSiCl2 (1; L 1 = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). This compound is formed under mild reaction conditions by reductive elimination of HCl from trichlorosilane in the presence of the NHC (L; Scheme 1), and was

Herbert W. Roesky

Papers

The interplay of coordinative, hydrogen bonding and π–π stacking interactions in sustaining supramolecular solid-state architectures.

Hetero- and Metallasiloxanes Derived from Silanediols, Disilanols, Silanetriols, and Trisilanols

Lewis Base Stabilized Dichlorosilylene

Synthesis and Structure of a Monomeric Aluminum(I) Compound [{HC(CMeNAr)2}Al] (Ar=2,6–iPr2C6H3): A Stable Aluminum Analogue of a Carbene

The Chemistry of Aluminum(I), Silicon(II), and Germanium(II)