Three different types of NH3 species can be simultaneously present on Cu(2+)-exchanged CHA-type zeolites, commonly used in Ammonia Selective Catalytic Reduction (NH3-SCR) systems. These include ammonium ions (NH4(+)), formed on the Brønsted acid sites, [Cu(NH3)4](2+) complexes, resulting from NH3 coordination with the Cu(2+) Lewis sites, and NH3 adsorbed on extra-framework Al (EFAl) species, in contrast to the only two reacting NH3 species recently reported on Cu-SSZ-13 zeolite. The NH4(+) ions react very slowly in comparison to NH3 coordinated to Cu(2+) ions and are likely to contribute little to the standard NH3-SCR process, with the Brønsted groups acting primarily as NH3 storage sites. The availability/reactivity of NH4(+) ions can be however, notably improved by submitting the zeolite to repeated exchanges with Cu(2+), accompanied by a remarkable enhancement in the low temperature activity. Moreover, the presence of EFAl species could also have a positive influence on the reaction rate of the available NH4(+) ions. These results have important implications for NH3 storage and availability in Cu-Chabazite-based NH3-SCR systems.

A combined theoretical and experimental study is performed in order to elucidate the effects of linker functional groups on the photoabsorption properties of UiO-66-X materials. This study, in which both mono- and difunctionalized linkers (with X = OH, NH2, or SH) are investigated, aims to obtain a more complete picture of the choice of functionalization. Static time-dependent density functional theory calculations combined with molecular dynamics simulations are performed on the linkers, and the results are compared to experimental UV/vis spectra in order to understand the electronic effects governing the absorption spectra. The disubstituted linkers show larger shifts than the monosubstituted variants, making them promising candidates for further study as photocatalysts. Next, the interaction between the linker and the inorganic part of the framework is theoretically investigated using a cluster model. The proposed ligand-to-metal-charge transfer is theoretically observed and is influenced by the differences in functionalization. Finally, the computed electronic properties of the periodic UiO-66 materials reveal that the band gap can be altered by linker functionalization and ranges from 4.0 down to 2.2 eV. Study of the periodic density of states allows the band gap modulations of the framework to be explained in terms of a functionalization-induced band in the band gap of the original UiO-66 host.

An enantioselective catalyst, consisting of a chiral Mn(III)salen complex entrapped in the MIL-101 metal organic framework, is reported. For the first time, we assemble a robust MOF-cage around a chiral complex. The heterogeneous catalyst shows the same selectivity as the homogeneous complex and is fully recyclable. Theoretical calculations provide insight into this retention of selectivity.

Ionizing radiation induces a composite, multiline electron paramagnetic resonance (EPR) spectrum in sucrose, that is stable at room temperature and whose intensity is indicative of the radiation dose. Recently, the three radicals which dominate this spectrum were identified and their proton hyperfine tensors were accurately determined. Understanding the powder EPR spectrum of irradiated sucrose, however, also requires an accurate knowledge of the g tensors of these radicals. We extracted these tensors from angular dependent electron nuclear double resonance-induced EPR measurements at 110 K and 34 GHz. Powder spectrum simulations using this completed set of spin Hamiltonian parameters are in good agreement with experimentally recorded spectra in a wide temperature and frequency range. However, as-yet nonidentified radicals also contribute to the EPR spectra of irradiated sucrose in a non-negligible way.

Ammonia-Selective Catalytic Reduction (NH 3 -SCR) using Cu-zeolites is a well-established strategy for the abatement of NO x 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 NH 3 -SCR relevant gases (NO and NH 3 ) with the Cu 2+ 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 ~ 150 °.While Cu seems to be partially reduced/changed in coordination state, NO is partially oxidized. On exposure to NH 3 whilst the PD data suggest the Cu 2+ ion occupies a similar position, simulation and XAFS pointed towards the formation of a Jahn-Teller distorted hexa-amine complex [Cu(NH 3 ) 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 NH 3 -SCR process.

In this paper an overview is presented of several approximations within Density Functional Theory (DFT) to calculate g-tensors in transition metal containing systems and a new accurate description of the spin-other-orbit contribution for high spin systems is suggested. Various implementations in a broad variety of software packages (ORCA, ADF, Gaussian, CP2K, GIPAW and BAND) are critically assessed on various aspects including (i) non-relativistic versus relativistic Hamiltonians, (ii) spin-orbit coupling contributions and (iii) the gauge. Particular attention is given to the level of accuracy that can be achieved for codes that allow g-tensor calculations under periodic boundary conditions, as these are ideally suited to efficiently describe extended condensed-phase systems containing transition metals. In periodic codes like CP2K and GIPAW, the g-tensor calculation schemes currently suffer from an incorrect treatment of the exchange spin-orbit interaction and a deficient description of the spin-other-orbit term. In this paper a protocol is proposed, making the predictions of the exchange part to the g-tensor shift more plausible. Focus is also put on the influence of the spin-other-orbit interaction which becomes of higher importance for high-spin systems. In a revisited derivation of the various terms arising from the two-electron spin-orbit and spin-other-orbit interaction (SOO), new insight has been obtained revealing amongst other issues new terms for the SOO contribution. The periodic CP2K code has been adapted in view of this new development. One of the objectives of this study is indeed a serious enhancement of the performance of periodic codes in predicting g-tensors in transition metal containing systems at the same level of accuracy as the most advanced but time consuming spin-orbit mean-field approach. The methods are first applied on rhodium carbide but afterwards extended to a broad test set of molecules containing transition metals from the fourth, fifth and sixth row of the periodic table. The set contains doublets as well as high-spin molecules.

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.

In order to find a reliable and efficient calculation scheme for electron paramagnetic resonance (EPR) spectroscopic parameters for transition metal complexes in ionic solids from first principles, periodic and finite cluster-in-vacuo density functional theory (DFT) simulations are performed for g tensors, ligand hyperfine tensors (A), and quadrupole tensors (Q) for Rh(2+)-related centers in NaCl. EPR experiments on NaCl:Rh single crystals identified three Rh(2+) monomer centers, only differing in the number of charge compensating vacancies in their local environment, and one dimer center. Periodic and cluster calculations, both based on periodically optimized structures, are able to reproduce experimentally observed trends in the ligand A and Q tensors and render very satisfactory numerical agreement with experiment. Taking also computation time into account as a criterion, a full periodic approach emerges as most appropriate for these parameters.The g tensor calculations, on the other hand, prove to be insufficiently accurate for model assessment. The calculations also reveal parameters of the complexes which are not directly accessible through experiments, in particular related to their geometry.