Unraveling the mechanism of the manganese-salen epoxidation

Chiral salen-type complexes are valuable catalysts for the antioselective epoxidation of unfunctionlized olefins. The mechanism of this reaction with the manganese-salen complex has always been the subject of an intense debate [1, 2]. The originally proposed mechanism featuring a radical intermediate seems to fail in explaining several experimental observations[3] and various alternatives have been proposed. However the obtained results were highly dependent of the chosen methodology. We will present a methodological study comparing a broad range of DFT functionals with high-level CASSCF calculations [4]. An OPBE functional was shown to be the most performant. Using this functional it is confirmed that the mechanism featuring a radical intermediate is indeed the most likely. Moreover it makes it possible to explain the experimental observations that did not fit in the classical model. For example olefins with a cyclopropane moiety next to the double bound result in a mixture of epoxides and ringopening products depending on the exact reaction conditions. Our calculations show that a radical reaction intermediate can lead to the observed product distribution. This methodology can thus prove to give more insights in the mechanism of this interesting catalyst, allowing it to be optimized further for numerous applications

Binary and ternary po-containing molecules relevant for LBE cooled reactors at operating temperature

Quantum-chemical calculations at several levels of theory were used to assess the stability at different temperatures of a set of 13 binary and ternary Po-containing molecules that could possibly be formed in an environment with lead, bismuth, oxygen and water. The conclusions are that especially PoPb, PbPoO and PoOH and to a lesser extent Po2 and PoO are stable. These small molecules are therefore likely to be found near the Lead-Bismuth eutectic (LBE) coolant at operational temperatures in a heavy liquid metal cooled fission reactor. In contrast, Po3 and PoBi are unlikely to be present under the assumed conditions. Several stability criteria, such as the dissociation into free atoms or into molecular fragments at realistic Po-concentrations or in the thermodynamic limit are discussed at different temperatures. The results obtained with a medium level of theory (Density Functional Theory, PBE0 with relativistic effective core potentials) show good qualitative correspondence with calculations performed at a much higher level of theory (Multi Reference Configuration Interaction, with spin–orbit coupling and scalar relativistic Hamiltonian)

Vibrational fingerprint of the absorption properties of UiO-type MOF materials

The absorption properties of UiO-type metal-organic frameworks are computed using TD-DFT simulations on the organic linkers. A set of nine isoreticular structures, including the UiO-66 and UiO-67 materials and functionalized variants, are examined. The excitation energies from a static geometry optimization are compared with dynamic averages obtained from sampling the ground-state potential energy surface using molecular dynamics. The vibrational modes that impact the excitation energy are identified. This analysis is done using a recently proposed tool based on power spectra of the velocities and the excitation energies. The applied procedure allows including important factors influencing the absorption spectra, such as the periodic framework, linker variation and dynamical effects including harmonic and anharmonic nuclear motions. This methodology allows investigating in detail the vibrational fingerprint of the excitation energy of advanced materials such as MOFs and gives perspectives to tailor materials toward new light-based applications

Determination of the nature of the Cu coordination complexes formed in the presence of NO and NH3 within SSZ-13

Ammonia-selective catalytic reduction (NH3-SCR) using Cu zeolites is a well-established strategy for the abatement of NOx gases. Recent studies have demonstrated that Cu is particularly active when exchanged into the SSZ-13 zeolite, and its location in either the 6r or 8r renders it an excellent model system for fundamental studies. In this work, we examine the interaction of NH3-SCR relevant gases (NO and NH3) with the Cu2+ centers within the SSZ-13 structure, coupling powder diffraction (PD), X-ray absorption spectroscopy (XAFS), and density functional theory (DFT). This combined approach revealed that, upon calcination, cooling and gas exposure Cu ions tend to locate in the 8r window. After NO introduction, Cu-ions are seen to coordinate to two framework oxygens and one NO molecule, resulting in a bent Cu-nitrosyl complex with a Cu-N-O bond angle of similar to 150 degrees. Whilst Cu seems to be partially reduced/changed in coordination state, NO is partially oxidized. On exposure to NH3 while the PD data suggest the Cu2+ ion occupies a similar position, simulation and XAFS pointed toward the formation of a Jahn-Teller distorted hexaamine complex [Cu(NH3)(6)](2+) in the center of the cha cage. These results have important implications in terms of uptake and storage of these reactive gases and potentially for the mechanisms involved in the NH3-SCR process

К уточнению понимания характеристик рынка труда

Рассмотрены основные характеристики рынка труда. Внесены предложения по их уточнению в соответствии с особенностями формирования регионального рынка труда.Розглянуті основні характеристики ринку праці. Внесено пропозиції по їхньому уточненню відповідно до особливостей формування регіонального ринку праці.Basic descriptions of labour-market are considered. Suggestions on their clarification in accordance with the features of forming of regional labour-market are borne