Thomas Bogaerts

Communication: DMRG-SCF study of the singlet, triplet, and quintet states of oxo-Mn(Salen)

We use CheMPS2, our free open-source spin-adapted implementation of the density matrix renormalization group (DMRG) [S. Wouters, W. Poelmans, P. W. Ayers, and D. Van Neck, Comput. Phys. Commun. 185, 1501 (2014)], to study the lowest singlet, triplet, and quintet states of the oxo-Mn(Salen) complex. We describe how an initial approximate DMRG calculation in a large active space around the Fermi level can be used to obtain a good set of starting orbitals for subsequent complete-active-space or DMRG self-consistent field calculations. This procedure mitigates the need for a localization procedure, followed by a manual selection of the active space. Per multiplicity, the same active space of 28 electrons in 22 orbitals (28e, 22o) is obtained with the 6-31G(*), cc-pVDZ, and ANO-RCC-VDZP basis sets (the latter with DKH2 scalar relativistic corrections). Our calculations provide new insight into the electronic structure of the quintet.

Mn-salen@MIL101(Al): a heterogeneous, enantioselective catalyst synthesized using a ‘bottle around the ship’ approach

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.

Bimetallic–Organic Framework as a Zero‐Leaching Catalyst in the Aerobic Oxidation of Cyclohexene

A gallium 2,2′‐bipyridine‐5,5′‐dicarboxylate metal–organic framework (MOF), denoted as COMOC‐4, has been synthesized by solvothermal synthesis. This MOF exhibits the same topology as MOF‐253. CuCl2 was incorporated into COMOC‐4 by a post‐synthetic modification (PSM). The spectroscopic absorption properties of the MOF framework before and after PSM were compared with theoretical data obtained by employing molecular dynamics combined with time‐dependent DFT calculations on both the as‐synthesized and functionalized linker. The catalytic behavior of the resulting Cu2+@COMOC‐4 material was evaluated in the aerobic oxidation of cyclohexene with isobutyraldehyde as a co‐oxidant. In addition, the catalytic performance of Cu2+@COMOC‐4 was compared with that of the commercially available Cu‐BTC (BTC=benzene‐1,3,5‐tricarboxylate) MOF. Cu2+@COMOC‐4 exhibits a good cyclohexene conversion and an excellent selectivity towards cyclohexene oxide in comparison to the Cu‐based reference catalyst. Furthermore, no leaching of the active Cu sites was observed during at least four consecutive runs.

Mechanistic Investigation on Oxygen Transfer with the Manganese‐Salen Complex

The best‐known application of salen complexes is the use of a chiral ligand loaded with manganese to form the Jacobsen complex. This organometallic catalyst is used in the epoxidation of unfunctionalized olefins and can achieve very high selectivities. Although this application was proposed many years ago, the mechanism of oxygen transfer remains a question until now. In this paper, the epoxidation mechanism is investigated by an ab initio kinetic modeling study. First of all a proper DFT functional is selected that yields the correct ordering of the various spin states. Our results show that the epoxidation proceeds via a radical intermediate. If we start from the radical intermediate, these results can explain the experiments with radical probes. The subtle influences in the transition state using the full Jacobsen catalyst explain the product distribution observed experimentally.

Fine-tuning the theoretically predicted structure of MIL-47(V) with the aid of powder X-ray diffraction

The structural characterization of complex crystalline materials such as metal organic frameworks can prove a very difficult challenge both for experimentalists as for theoreticians. From theory, the flat potential energy surface of these highly flexible structures often leads to different geometries that are energetically very close to each other. In this work a distinction between various computationally determined structures is made by comparing experimental and theoretically derived X-ray diffractograms which are produced from the materials geometry. The presented approach allows to choose the most appropriate geometry of a MIL-47(V) MOF and even distinguish between different electronic configurations that induce small structural changes. Moreover the techniques presented here are used to verify the applicability of a newly developed force field for this material. The discussed methodology is of significant importance for modelling studies where accurate geometries are crucial, such as mechanical properties and adsorption of guest molecules.