Thermodynamic and kinetic data for adduct formation, cis-trans isomerization and redox reactions of ML4 complexes: a case study with rhodium- and iridium-tropp complexes in d8, d9 and d10 valence electron configurations (tropp=dibenzotropylidene phosphanes)

The formation of adducts of the square-planar 16-electron complexes trans-[M(tropp(ph))(2)](+) and cis-[M(tropp(ph))(2)](+) (M=Rh, Ir; tropp(Ph)=5-diphenylphosphanyldibenzo[a,d]cycloheptene) with acetonitrile (acn) and Cl(-), and the redox chemistry of these complexes was investigated by various physical methods (NMR and UV-visible spectroscopy, square-wave voltammetry), in order to obtain some fundamental thermodynamic and kinetic data for these systems. A trans/cis isomerization cannot be detected for [M(tropp(ph))(2)](+) in non-coordinating solvents. However, both isomers are connected through equilibria of the type trans-[M(tropp(ph))(2)](+)+L<==>[ML(tropp(ph))(2)](n)<==>cis-[M(tropp(ph))(2)](+)+L, involving five-coordinate intermediates [ML(tropp(ph))(2)](n) (L=acn, n=+1; L=Cl(-), n=0). Values for K(d) (K(f)), that is, the dissociation (formation) equilibrium constant, and k(d) (k(f)), that is, the dissociation (formation) rate constant, were obtained. The formation reactions are fast, especially with the trans isomers (k(f)>1x10(5) m(-1) s(-1)). The reaction with the sterically more hindered cis isomers is at least one order of magnitude slower. The stability of the five-coordinate complexes [ML(tropp(ph))(2)](n) increases with Ir>Rh and Cl(-)>acn. The dissociation reaction has a pronounced influence on the square-wave (SW) voltammograms of trans/cis-[Ir(tropp(ph))(2)](+). With the help of the thermodynamic and kinetic data independently determined by other physical means, these reactions could be simulated and allowed the setting up of a reaction sequence. Examination of the data obtained showed that the trans/cis isomerization is a process with a low activation barrier for the four-coordinate 17-electron complexes [M(tropp(ph))(2)](0) and especially that a disproportionation reaction 2 trans/cis-[M(tropp(ph))(2)](0)-->[M(tropp(ph))(2)](+)+[M(tropp(ph))(2)](-) may be sufficiently fast to mask the true reactivity of the paramagnetic species, which are probably less reactive than their diamagnetic equilibrium partners.     

Very Facile Polarity Umpolung and Noncovalent Functionalization of Inorganic Nanoparticles: A Tool Kit for Supramolecular Materials Chemistry

The facile assembly of shell‐by‐shell (SbS)‐coated nanoparticles [TiO₂?PAC₁₆]@shell 1 – 7 (PAC₁₆=hexadecylphosphonic acid), which are soluble in water and can be isolated as stable solids, is reported. In these functional architectures, an umpolung of dispersibility (organic apolar versus water) was accomplished by the noncovalent binding of ligands 1 – 7 to titania nanoparticles [TiO₂?PAC₁₆] containing a first covalent coating with PAC₁₆. Ligands 1 – 7 are amphiphilic and form the outer second shell of [TiO₂?PAC₁₆]@shell 1 – 7 . The tailor‐designed dendritic building blocks 3 – 5 contain negative and positive charges in the same molecule, and ligands 6 and 7 contain a perylenetetracarboxylic acid dimide (PDI) core ( 6 / 7 ) as a photoactive reporter component. In the redox and photoactive system [TiO₂?PAC₁₆]@shell 7 , electronic communication between the inorganic core to the PDI ligands was observed.     

A formula for the determinant of a sum of matrices

We give a formula, involving circular words and symmetric functions of the eigenvalues, for the determinant of a sum of matrices. Theorem of Hamilton-Cayley is deduced from this formula.UQAM and LITPUniversité Paris 7 and LITP.     

Search for supersymmetry at the LHC in events with jets and missing transverse energy

A search for events with jets and missing transverse energy is performed in a data sample of pp collisions collected at √s=7 TeV by the CMS experiment at the LHC. The analyzed data sample corresponds to an integrated luminosity of 1.14 fb(-1). In this search, a kinematic variable α(T) is used as the main discriminator between events with genuine and misreconstructed missing transverse energy. No excess of events over the standard model expectation is found. Exclusion limits in the parameter space of the constrained minimal supersymmetric extension of the standard model are set. In this model, squark masses below 1.1 TeV are excluded at 95% C.L. Gluino masses below 1.1 TeV are also ruled out at 95% C.L. for values of the universal scalar mass parameter below 500 GeV.     

Long-term variability of global statistical properties of epileptic brain networks

We investigate the influence of various pathophysiologic and physiologic processes on global statistical properties of epileptic brain networks. We construct binary functional networks from long-term, multichannel electroencephalographic data recorded from 13 epilepsy patients, and the average shortest path length and the clustering coefficient serve as global statistical network characteristics. For time-resolved estimates of these characteristics we observe large fluctuations over time, however, with some periodic temporal structure. These fluctuations can--to a large extent--be attributed to daily rhythms while relevant aspects of the epileptic process contribute only marginally. Particularly, we could not observe clear cut changes in network states that can be regarded as predictive of an impending seizure. Our findings are of particular relevance for studies aiming at an improved understanding of the epileptic process with graph-theoretical approaches.     

Evidence for high-m secondary islands induced by large low-m islands in a tokamak plasma

Small-scale structures with high poloidal mode numbers (m=10-20) have been observed in the TEXTOR tokamak plasma with pulsed radar reflectometry and an electron cyclotron emission diagnostic, in conjunction with large 2/1 and 1/1 islands. The small islands have a peaked density profile, similar to that of the simultaneously observed large-scale 2/1 islands. This together with the observation that high-frequency density and temperature fluctuations are very pronounced near the X points of the large islands hints to a strongly perturbed magnetic topology around the X points.     

Reversible Mechanical Switching of Magnetic Interactions in a Molecular Shuttle

An acid–base switchable molecular shuttle based on a [2]rotaxane, incorporating stable radical units in both the ring and dumbbell components, is reported. The [2]rotaxane comprises a dibenzo[24]crown-8 ring (DB24C8) interlocked with a dumbbell component that possesses a dialkylammonium (NH₂⁺) and a 4,4′-bipyridinium (BPY²⁺) recognition site. Deprotonation of the rotaxane NH₂⁺ centers effects a quantitative displacement of the DB24C8 macroring to the BPY²⁺ recognition site, a process that can be reversed by acid treatment. Interaction between stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals connected to the ring and dumbbell components could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon displacement of the spin-labelled DB24C8 macroring. The complete base- and acid-induced switching cycle of the EPR pattern was repeated six times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. A system of this kind represents an initial step towards a new generation of nanoscale magnetic switches that may be of interest for a variety of applications.