Synthesis of a “Butterfly Cage” Based on a Double‐Decker Silsesquioxane

Novel polyhedral structures were prepared with a butterfly‐shape composed of oligosiloxane wings and a double‐decker silsesquioxane (DDSQ) body. The compounds were synthesized in two steps from commercially available alkoxysilanes, and their structures were confirmed using spectroscopic methods and X‐ray crystallography. Not like other phenyl‐substituted cage silsesquioxanes, these butterfly cages show very good solubility in common organic solvents. The crystal structures clearly showed their unique features: a larger space with longer siloxane chains and a very flexible framework. Moreover, these compounds are thermally stable with a Td₅ (5 % weight loss temperature) over 320 °C.     

Interfaces between Molecular and Polymeric “Metals”: Electrically Conductive,Structure-Enforced Assemblies of Metallomacrocycles

The design, synthesis, characterization, and understanding of new molecular and macro-molecular substances with “metal-like” electrical properties represents an active research area at the interface of chemistry, physics, and materials science. An important, long-range goal in this field of “materials by design” is to construct supermolecular assemblies which exhibit preordained collective phenomena by virtue of “engineered” interactions between molecular building blocks. In this review, such a class of designed materials is discussed which, in addition, bridges the gap between molecular and polymeric conductors: assemblies of electrically conductive metallomacrocycles. It is seen that efforts to rationally construct stacked metal-like molecular arrays lead logically to structure-enforced macromolecular assemblies of covalently linked molecular subunits. Typical building blocks are robust, chemically versatile metallophthalocyanines. The electrical optical, and magnetic properties of these metallomacrocyclic assemblies and the fragments thereof, provide fundamental information on the connections between local atomic-scale architecture, electronic structure, and the macroscopic collective properties of the bulk solid.     

Growth and Dissolution of Organic Crystals with “Tailor-Made” Inhibitors—Implications in Stereochemistry and Materials Science

When crystals of organic compounds are grown in the presence of growth inhibitors, there is a change in crystal morphology. A stereochemical correlation exists between the crystal structure, its modified morphology, and the molecular structure of the inhibitor. This correlation has been successfully exploited for the efficient resolution of conglomerates, the engineering of organic crystals with desired morphologies, the direct and relative assignment of the absolute configurations of chiral molecules and crystals, and for the design of a new model for the spontaneous generation of optical activity. In an analogous way dissolution of organic crystals in the presence of these growth inhibitors induces etch pits at preselected faces. The effect of solvent on crystal growth has been analyzed in some model systems. The experimental results are complemented by atom-atom potential energy calculations.     

Platinum Group Organometallics Based on “Pincer” Complexes: Sensors,Switches, and Catalysts

Since the first reports in the late 1970s on transition metal complexes containing pincer‐type ligands—named after the particular coordination mode of these ligands—these systems have attracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typically, such a ligand comprises an anionic aryl ring which is ortho,ortho‐disubstituted with heteroatom substituents, for example, CH₂NR₂, CH₂PR₂ or CH₂SR, which generally coordinate to the metal center, and therefore support the M−C σ bond. This commonly results in a terdentate and meridional coordination mode consisting of two metallacycles which share the M−C bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental understanding of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mechanistic elucidation of fundamental transformations (for example, C−C bond activation), the construction of the first metallodendrimers for sustainable homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous investigations. This review discusses the synthetic methodologies that are currently available for the preparation of platinum group metal complexes containing pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineering of sensors, switches, and catalysts.