Kurt Merzweiler

Bio: Kurt Merzweiler is an academic researcher from Martin Luther University of Halle-Wittenberg. The author has contributed to research in topic(s): Crystal structure & Cluster (physics). The author has an hindex of 17, co-authored 162 publication(s) receiving 1497 citation(s).

New Transition Metal Clusters with Ligands from Main Groups Five and Six

Abstract: In both physics and chemistry, increased attention is being paid to metal clusters. One reason for this attitude is furnished by the surprising results that have been obtained from studies of the preparation, structural characterization and physical and chemical properties of the clusters. Whereas investigations of cluster reactivity are at present generally limited to three- or four-membered clusters, successful syntheses of clusters with many more metal atoms have recently been designed. These substances occupy an intermediate position between solid state chemistry and the chemistry of metal complexes. This review presents a versatile method for synthesizing metal clusters: the reaction of complexes of transition metal halides with silylated compounds such as E(SiMe3)2 (E = S, Se, Te) and E′R(SiMe3)2 (R = Ph, Me, Et; E′ = P, As, Sb). Although some of the compounds thus formed have already been prepared by other routes, the method affords ready access to both small and large transition metal clusters with unusual structures and valence electron concentrations; a variety of reactions in the ligand sphere are also possible.

Neue Übergangsmetallcluster‐Komplexe mit Liganden der fünften und sechsten Hauptgruppe

Abstract: Metallclustern wird in der Chemie und der Physik zunehmend Beachtung geschenkt, vor allem wegen der uberraschenden Resultate, die in vielen Fallen mit der Synthese und Strukturaufklarung sowie dem Studium der physikalischen und chemischen Eigenschaften dieser Verbindungen einhergehen. Wahrend Untersuchungen der Reaktivitat von Metallclustern gegenwartig im wesentlichen auf drei- und vierkernige Cluster beschrankt sind, konnten in jungster Zeit auch Synthesen fur Cluster mit sehr vielen Metallatomen entwickelt werden. Mit diesen Substanzen lassen sich moglicherweise Brucken zwischen der Festkorperchemie und der Komplexchemie schlagen. In dieser Ubersicht wird ein vielseitig anwendbares und ausbaufahiges Verfahren zur Synthese von Metallclustern beschrieben. Dazu werden Ubergangsmetallhalogenid-Komplexe mit silylierten Verbindungen wie E(SiMe3)2 (E = S, Se, Te) und E′R(SiMe3)2 (R = Ph, Me, Et; E′ = P, As, Sb) umgesetzt. Diese Methode bietet einen einfachen Zugang zu nieder- und hochmolekularen Ubergangsmetallclustern mit ungewohnlichen Strukturen und Valenzelektronenkonzentrationen sowie vielfaltigen Reaktionsmoglichkeiten in der Ligandensphare.

Unexpected liquid crystalline behaviour of three-ring bent-core mesogens: bis(4-subst.-phenyl) 2-methyl-iso-phthalates

Abstract: Three-ring bent-core bis(4-subst.-phenyl) 2-methyl-iso-phthalates exhibiting nematic, SmA and SmC phases are reported. The occurring mesophases have been identified by their optical textures and X-ray diffraction measurements which give also geometrical structural parameters like layer spacing and molecular tilt. Quantum chemical calculations on single molecules and X-ray structure analysis in the crystalline state indicate wide opening angles (about 155°) of the molecular legs due to the lateral methyl group in position 2 of the central phenyl ring. However solid state NMR spectroscopy in the liquid crystalline phases finds stronger molecular bending (bending angle to be about 138° in the SmA and about 146° in the nematic phase). Dielectric and SHG measurements give evidence that in the SmA phase a polar structure can be induced by application of an electric field which disappears in the isotropic liquid phase. The electric field not only leads to a slight textural change even in the SmA phase but also polar-type electric current response (PS about 200 nC cm−2) is observed. This unusual electro-optical behaviour is discussed on the basis of the orientation of polar clusters formed by the bent molecules. In the paper we not only attempt to characterize the mesophases and to describe their physical properties, but we also show that these types of molecules represent the borderline between bent-shaped and calamitic liquid crystals.

Helicascolide C, a new lactone from an Indonesian marine algicolous strain of Daldinia eschscholzii (Xylariaceae, Ascomycota)

Abstract: From an endophytic Daldinia eschscholzii strain isolated from the agar-producing red alga Gracilaria sp. SGR-1, collected from the coast of South Sulawesi, Indonesia, a new lactone helicascolide C (1) was obtained as colourless crystals from the ethyl acetate extract together with the related structurally known compound helicascolide A (2). The structure of the new compound 1 reveals a carbonyl group replacing an alcohol group of compound 2. The structure of 1 was elucidated by X-ray diffraction and spectral analyses. Compound 1 showed fungistatic activity against the phytopathogenic fungus Cladosporium cucumerinum.

Synthesis and Characterization of Platina-β-diketones.

Abstract: Summary: Hexachloroplatinic acid reacts with n-butanol to give the but-2-ene complex H[PtCl3(η2-C4H8)] (3) as intermediate, which reacts with trimethylsilyl-substituted acetylenes R‘C⋮CSiMe3 (R‘ = H, Me, SiMe3) with cleavage of the silyl groups to form platina-β-diketones [Pt2(μ-Cl)2{(COR)2H}2] [R = Me (2a), Et (2b)]. The constitution of 2 was determined by microanalysis, NMR (1H, 13C) spectroscopy, IR, Raman, and mass spectroscopy. The structure of 2a was determined by X-ray diffraction.

Marine natural products.

Abstract: This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1378 in 456 papers for 2014), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Colloidal Semiconductor Q‐Particles: Chemistry in the Transition Region Between Solid State and Molecules

Abstract: In semiconductor particles of nanometer size, a gradual transition from solid-state to molecular structure occurs as the particle size decreases. Consequently, a splitting of the energy bands into discrete, quantized levels occurs. Particles that exhibit these quantization effects are often called “Q-particles” or, generally, quantized material. The optical, electronic and catalytic properties of Q-particles drastically differ from those of the corresponding macrocrystalline substance. The band gap, a substance-specific quantity in macrocrystalline materials, increases by several electron volts in Q-particles with decreasing particle size. In Q-particles there are approximately as many molecules on the surface as in the interior of the particle. Therefore, the nature of the surface as well as the particle size is also largely responsible for the physico-chemical properties of the particle. Q-particles of many materials can be prepared in the form of colloidal solutions or embedded in porous matrices and are stable over a long period of time. In sandwich colloids, in which Q-particles of different materials are coupled, as well as in porous semiconductor electrodes containing Q-particles in the pores, very efficient primary charge separation is observed. As a result, sandwich colloids have greatly enhanced photocatalytic activity relative to the individual particles, while electrodes modified with Q-particles show high photocurrents. This article deals with the size quantization effect, the synthesis and characterization of Q-particles, as well as with the spectroscopic, electrochemical, and electron-microscopic investigation of these particles.

Quantum sized, thiolate-protected gold nanoclusters

Abstract: The scientific study of gold nanoparticles (typically 1–100 nm) has spanned more than 150 years since Faraday's time and will apparently last longer. This review will focus on a special type of ultrasmall (<2 nm) yet robust gold nanoparticles that are protected by thiolates, so-called gold thiolate nanoclusters, denoted as Aun(SR)m (where, n and m represent the number of gold atoms and thiolate ligands, respectively). Despite the past fifteen years' intense work on Aun(SR)m nanoclusters, there is still a tremendous amount of science that is not yet understood, which is mainly hampered by the unavailability of atomically precise Aun(SR)m clusters and by their unknown structures. Nonetheless, recent research advances have opened an avenue to achieving the precise control of Aun(SR)m nanoclusters at the ultimate atomic level. The successful structural determination of Au102(SPhCOOH)44 and [Au25(SCH2CH2Ph)18]q (q = −1, 0) by X-ray crystallography has shed some light on the unique atomic packing structure adopted in these gold thiolate nanoclusters, and has also permitted a precise correlation of their structure with properties, including electronic, optical and magnetic properties. Some exciting research is anticipated to take place in the next few years and may stimulate a long-lasting and wider scientific and technological interest in this special type of Au nanoparticles.

Molecular tectonics in biomineralization and biomimetic materials chemistry

Abstract: The systematic fabrication of advanced materials will require the construction of architectures over scales ranging from the molecular to the macroscopic. The basic constructional processes of biomineralization—supramolecular pre-organization, interfacial molecular recognition (templating) and cellular processing—can provide useful archetypes for molecular-scale building, or ‘molecular tectonics’, in inorganic materials chemistry.