Dedicated to Professor Hans Bock on the occasion of his 60th birthdayIn 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(SiMe,)' (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.

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.

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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 (P S about 200 nC cm À2 ) is observed. This unusual electrooptical 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.