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L. Getzner:
"Catalytic study of polymeric spin crossover iron(II) triazole complexes: A  first step to switchable catalysis";
Supervisor: W. Linert, K. Föttinger, G. Madsen; Institut für Angewandte Synthesechemie, 2021; final examination: 2021-11-30.

With the rise of more complex chemical compounds and materials, new strategies are always needed, especially in regards to the catalysis of chemical reactions. Therefore, switchable catalysis has emerged as a promising  eld for the development of highly controllable catalytic systems that, triggered by e.g. light irradiation, temperature changes or chemical stimuli, can intrinsically modify a reaction. To accomplish this, materials that are inherently switchable between two or more stable states and at the same time able to act as a catalyst are needed. The spin crossover phenomenon is an example for molecular bistability found mainly in 3d4 to 3d7 transition metal centres in an octahedral ligand  eld. A well known family of SCO materials with tunable spin transition properties are the one-dimensional iron(II) triazole coordination polymers, where the iron centres are bridged by 4-R-1,2,4-triazole ligands. The purpose of this thesis is to implement the one-dimensional iron(II) spin crossover coordination polymer [Fe(NH2trz)3](NO3)2 as a switchable catalyst and to test its spin state dependent ability to catalyse an acetalisation reaction. The SCO material exhibits an abrupt spin transition above room temperature that is preserved during the reaction, with a large hysteresis loop enabling a direct comparison of the catalytic reaction in low-spin and high-spin states at otherwise identical conditions. It is shown that [Fe(NH2trz)3](NO3)2 is able to successfully catalyse the acetalisation reaction of various aromatic aldehydes. Moreover, a de nite increase in yield is observed when the catalyst is used in HS state instead of LS state. As the activation energies for both spin states are ascertained to be in the same range, the increase in yield is attributed to the increased access of the substrate to catalytically active sites in HS state due to a shift in the arrangement of polymer chains. Many additional experiments are performed to determine the in uence of solvent changes, water or impurities and to elucidate the reaction mechanism.

Spin crossover, Catylysis, Triazole