Particle formation can occur by way of a classical or non-classical nucleation pathway. We show that during the bottom-up synthesis of cobalt particles the degree of particle surface stabilization determines the formation pathway. Without additives, young cobalt particles are liquid because of the size-dependent melting point depression, and crystallization starts only after growth by coalescence, in accord to a non-classical pathway. Addition of surfactants during synthesis leads to particle surface stabilization and, thus, an elevated melting point such that a crystalline nucleus is formed in a classical pathway.

In the flourishing chemistry of divalent silicon, π-complex formation between silicon and the pentamethylcyclopentadienyl (Cp*) group is one of the successful strategies for thermodynamic and/or kinetic stabilization. Here, the diverse reactivity of the [Cp*Si](+) ion is described. Its chemistry is characterized by the addition of anionic and neutral nucleophiles and by the easy hapticity change and the leaving-group character of the Cp* group. Several novel sandwich and half-sandwich π-complexes of divalent silicon were synthesized, and a novel access to the class of cyclotrisilenes was found. A reversible adduct formation is the basis for the catalytic activity of the [Cp*Si](+) ion in the specific oligoether degradation. Homo- or heterolytic Cp*-Si bond cleavage allows the use of the cation as a source of silicon atoms in silicon cluster synthesis and in nanoparticle formation.

SiSi-Aktivierung: Die reversible Bildung eines Donor-Akzeptor-Komplexes zwischen einem N-heterocyclischen Carben und einem Cyclotrisilen mit C-Substituenten verschiebt die Elektronendichte der Doppelbindung und induziert somit eine starke Polarisierung, wie durch das signifikant pyramidale dreifachkoordinierte Siliciumatom verdeutlicht wird.

During the last few decades, alkene and alkyne analogues of the heavier Group 14 elements have attracted considerable interest. Their isolation as stable derivatives has become possible by the use of carefully designed bulky substituents that provide kinetic (and to some extent thermodynamic) stabilization. The considerable differences in structure, bonding, and reactivity of such compounds in comparison to the carbon-based species have prompted various experimental and theoretical studies. By and large, the lower electronegativity of heavier elements and the increasing spatial extension of their valence electron shells are responsible for many of these differences. One of several rationalizations for structure and reactivity of such doubly and triply bonded species is based on zwitterionic (Ib and IIb in Scheme 1) and

The Cp*Si(+) cation acts as a stoichiometric source of silicon in the reaction with the disilenide Tip(2)Si=Si(Tip)Li (Tip = 2,4,6-(i)Pr(3)C(6)H(2)) affording known neutral unsaturated silicon clusters. It thereby provides a conceptually different approach to this novel class of compounds. The proposed mechanism involves a Cp*-substituted cyclotrisilene in which Cp*(-) acts as a leaving group upon single electron reduction or in a nucleophilic substitution step.

In the presence of ionic compounds, the thermal decomposition of octacarbonyldicobalt, Co-2(CO)(8), in an inert solvent leads exclusively to epsilon-Co nanocubes. The ionic species can be added directly or generated in situ by a chemical reaction between an additive and the precursor or between two additives. The additional presence of an inhomogeneous magnetic field leads to disc-shaped crystalline nanoparticles, which assemble to chains.

This paper highlights recent advances in synthesis and magnetotransport properties of magnetic Co nanopartides. It is shown that magnetic Co nanoparticles self-assembled in nanoparticular monolayers revealing giant magnetoresistance similar to granular systems but with additional features resulting from dipolar interactions between small domains of nanoparticles. A spin-valve with one magnetic Co nanoparticular electrode is employed as a model to demonstrate that individual magnetic moments of Co nanoparticles can be coupled to a magnetic Co layer which in turn offers tailoring of the resulting giant magnetoresistance characteristics. In addition, it is demonstrated that combining a magnetic on-off ratchet with magnetic tunneling junctions integrated in the ratchet introduces a new biosensor concept enabling: (1) simultaneous transporting and separating biomolecules, (2) dynamical biomolecule detection when passing magnetic tunneling junctions in a 1D arrangement. It is projected that this biosensor concept could be applied for viruses as well as for bacteria.

The synthesis of multipodes based on substituted ferrocene groups and the results of the investigations of the liquid-crystalline phase properties of these materials, determined by optical polarising microscopy DSC and X-ray diffraction studies as central cores is reported.

Die grundsätzliche Frage, wie Silicium mit der Antiaromatizität in Vierring-Systemen umgeht, wurde durch die Synthese und Charakterisierung des ersten Tetrasilacyclobutadiens, Si4Ar4 (1), und des ersten dimeren Silaisonitrils, Si2(NAr′)2 (2), beantwortet. 1 wird am besten durch die Resonanzstruktur 1′ mit Ladungstrennung und 2 durch eine Struktur mit π-artigen Elektronenpaaren an den N-Atomen und leeren π-Orbitalen an den Si-Atomen beschrieben.

The fundamental question of how silicon handles antiaromaticity in four-membered ring systems has been answered by the synthesis and characterization of the first tetrasilacyclobutadiene Si4Ar4 (1) and by the first dimeric silaisonitrile Si2(NAr′)2 (2). Compound 1 is best described by the charge-separated resonance structure 1′ and 2 by a structure with π-type lone pairs at the nitrogen atoms and vacant π orbitals at the silicon atoms.

Routes are presented for synthesizing nano- and mesostructured β-tin particles in the form of monocrystalline spheres, cubes, and bars, as well as polycrystalline rods and needles, by the decomposition of decamethylstannocene in organic solvents under various conditions. The formation of the observed shapes is based on the presence of liquidlike and of partly crystalline droplets. These particle stages allow structure-determining processes such as entire coalescence, oriented superficial coalescence or superficial induced crystallization. Entire coalescence and oriented superficial coalescence take place in the absence of surfactants; the superficially induced crystallization occurs in the presence of ionic additives. The observed tin morphologies depend on the competition between droplet growth and crystallization behavior. The different tin particles are investigated by electron microscopy (SEM, TEM, HRTEM), selected area electron diffraction (SAED), and differential scanning calorimetry (DSC).

Der ungewöhnliche Katalysator Cp*Si+ kann Oligo(ethylenglycol)-Diether RO(CH2CH2O)nR abbauen (siehe Schema). An seiner offenen Si-Koordinationssphäre können bis zu vier Si-O-Kontakte gebildet werden. Kristallstrukturdaten der reaktiven Verbindungen [Cp*Si(dme)]+BR4− und [Cp*Si([12]Krone-4)]+BR4− (R=C6F5) zeigen schwach gebundene Ethermoleküle.

Reaction of the (pentamethylcyclopentadienyl)silicon cation with the (pentamethylcyclopentadienyl)dicarbonylferrate anion leads to the formation of the crystalline, thermolabile silicon(II) compound [(eta(5)-pentamethylcyclopentadienyl)dicarbonylferrio](eta(3)-pentamethylcyclopentadienyl)silicon. The singlet triplet energy difference Delta E-ST is calculated to be 25.4 kcal/mol.

This article reviews recent developments on magnetoresistive detection of magnetic beads or nanoparticles by nanoscale sized sensors. Sensors are analyzed from an experimental and a numerical point of view in respect to their capability to either localize the position of a single magnetic particle or to detect the number of particles in a certain range. Guidelines are shown up on how to extend single sensors to sensor arrays with very high spatial resolution and how to modify the sensor shape in order to provide long distance measurements. Further, sensors in biological lab-on-a-chip environments are discussed. The magnetic ratchet and a gravitation based microfluidic component are reviewed as important tools to position and, therefore, detect biological components in continuous-flow devices.

Ab-initio calculations have been performed for the half-sandwich cation [(Me5C5)Si]+ and its DME complex [(Me5C5)Si(DME)]+. For these cations, the ground state energies, the complexation energy, the frontier orbitals, the vertical singlet-triplet excitation energies, and the natural atomic charges have been calculated. In both cations, the “lone-pair” at silicon does not represent the HOMO. The nature of the weak dative O → Si bond can best be described in terms of electrostatic and attractive dispersion interactions. The DME coordination destabilizes the cluster orbitals and slightly enhances the positive charge at silicon.

The etherification of the hydroxyl group of citric acid with saturated and unsaturated long-chain alkyl groups is described. This is a new approach to polydentate acids which may serve as ligands for metal or metal oxide nanoparticles. For this purpose we developed a synthetic route to long-chain ω-unsaturated alcohols and their triflate derivatives.