Substitution reactions with [ReBr(2)(CO)(2)(NCCH(3))(2)](-): a convenient route to complexes with the cis-[Re(CO)(2)](+) core

Water- and air-stable complexes comprising the cis-[Re(CO)(2)](+) core can be synthesized from the (Et(4)N)[ReBr(2)(NCCH(3))(2)(CO)(2)] precursor . Complex showed distinctly different chemical and electronic behaviour compared to [ReBr(3)(CO)(3)](2-). Substituting the two bromides in with imidazole-like ligands or alpha,alpha'-diimines gave new complexes with potential applications in bioinorganic chemistry and photochemistry. The two acetonitrile ligands are very stably bound and could not be replaced. Under CO pressure, the uncommon complex mer-[ReBr(NCCH(3))(2)(CO)(3)] was formed from . The reaction of with the tetradentate ligand bis(2-pyridylmethyl)glycine (BPG) finally induced a four fold substitution at the metal center to form a [Re(CO)(2)(L(4))](+)-type complex.     

Sharp bounds for the valence of certain harmonic polynomials

In Khavinson and Swiatek (2002) it was proved that harmonic polynomials , where is a holomorphic polynomial of degree , have at most complex zeros. We show that this bound is sharp for all by proving a conjecture of Sarason and Crofoot about the existence of certain extremal polynomials . We also count the number of equivalence classes of these polynomials.

     

All the disorder mechanisms in the 13:58 phases come together. Out of the modulated confusion rises the remarkable phase Ce12.60Cd58.68(2)

The compound Ce12.60Cd58.68(2) is a metrically commensurate representative of the incommensurately modulated phase Ce13Cd57+delta. It is most likely a lock-in phase. The structure, which was solved using seeding of the modulation from those positions most affected as well as direct solution by charge flipping, represents a rare case of ordering in a family of structures where disorder is the rule. The disorder mechanisms, known from other RE13Zn/Cd58 phases, order in this phase to give rise to a remarkable interplay between interstitials and vacancies. The compound crystallizes in the super space group Ccmm(alpha00)00s (standard setting Amma(00gamma)s00) with cell parameters a=27.2789(14) A, b=15.7592(1) A, and c=15.5816(4) A and a q vector close to 2/3.     

A Reactive Molecular Dynamics Study of Chlorinated Organic Compounds. Part II: A ChemTraYzer Study of Chlorinated Dibenzofuran Formation and Decomposition Processes

In our two-paper series, we first present the development of ReaxFF CHOCl parameters using the recently published ParAMS parametrization tool. In this second part, we update the reactive Molecular Dynamics – Quantum Mechanics coupling scheme ChemTraYzer and combine it with our new ReaxFF parameters from Part I to study formation and decomposition processes of chlorinated dibenzofurans. We introduce a self-learning method for recovering failed transition-state searches that improves the overall ChemTraYzer transition-state search success rate by 10 percentage points to a total of 48 %. With ChemTraYzer, we automatically find and quantify more than 500 reactions using transition state theory and DFT. Among the discovered chlorinated dibenzofuran reactions are numerous reactions that are new to the literature. In three case studies, we discuss the set of reactions that are most relevant to the dibenzofuran literature: (i) bimolecular reactions of the chlorinated-dibenzofuran precursors phenoxy radical and 1,3,5-trichlorobenzene, (ii) dibenzofuran chlorination and pyrolysis, and (iii) oxidation of chlorinated dibenzofurans.     

Practical use of robust GCV and modified GCV for spline smoothing

Generalized cross-validation (GCV) is a popular parameter selection criterion for spline smoothing of noisy data, but it sometimes yields a severely undersmoothed estimate, especially if the sample size is small. Robust GCV (RGCV) and modified GCV are stable extensions of GCV, with the degree of stabilization depending on a parameter \(\gamma \in (0,1)\) for RGCV and on a parameter \(\rho >1\) for modified GCV. While there are favorable asymptotic results about the performance of RGCV and modified GCV, little is known for finite samples. In a large simulation study with cubic splines, we investigate the behavior of the optimal values of \(\gamma \) and \(\rho \), and identify simple practical rules to choose them that are close to optimal. With these rules, both RGCV and modified GCV perform significantly better than GCV. The performance is defined in terms of the Sobolev error, which is shown by example to be more consistent with a visual assessment of the fit than the prediction error (average squared error). The results are consistent with known asymptotic results.     

UV‐Free Microfluidic Particle Fabrication at Low Temperature Using ARGET‐ATRP as the Initiator System

A new way to fabricate monodisperse polymer particles in a microfluidic device without UV‐light and without the need for high temperatures is described in this article. By applying an activator regeneration by electron transfer ‐ atom transfer radical polymerization (ARGET‐ATRP) initiator system in a co‐capillary microfluidic setup and by separating the monomer mixture in an initiator and a catalyst phase, a fast polymerization of the droplets at low temperature without premature curing and thus clogging of the capillaries can be achieved. The influence of the flow rates on the particle sizes and their polydispersity as well as the controlled character of the polymerization are investigated. The particle size is well adjustable, but the reaction is not controlled due to the high radical concentration needed for rapid polymerization. In addition, particles with incorporated UV‐dyes are produced as a proof of concept at low temperature.