Browsing by Author "Jäger, René"

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Open Access
Electrochemistry and spin‐crossover behavior of fluorinated terpyridine‐based Co(II) and Fe(II) complexes
(2023) Nößler, Maite; Jäger, René; Hunger, David; Reimann, Marc; Bens, Tobias; Neuman, Nicolás I.; Singha Hazari, Arijit; Kaupp, Martin; Slageren, Joris van; Sarkar, Biprajit
Due to their ability to form stable molecular complexes that have tailor-made properties, terpyridine ligands are of great interest in chemistry and material science. In this regard, we prepared two terpyridine ligands with two different fluorinated phenyl rings on the backbone. The corresponding CoII and FeII complexes were synthesized and characterized by single-crystal X-ray structural analysis, electrochemistry and temperature-dependent SQUID magnetometry. Single crystal X-ray diffraction analyses at 100 K of these complexes revealed Co-N and Fe-N bond lengths that are typical of low spin CoII and FeII centers. The metal centers are coordinated in an octahedral fashion and the fluorinated phenyl rings on the backbone are twisted out of the plane of the terpyridine unit. The complexes were investigated with cyclic voltammetry and UV/Vis-NIR spectroelectrochemistry. All complexes show a reversible oxidation and several reduction processes. Temperature dependent SQUID magnetometry revealed a gradual thermal SCO behavior in two of the complexes, while EPR spectroscopy provided further insights on the electronic structure of the metal complexes, as well as site of reduction.
Open Access
Spin crossover and fluorine‐specific interactions in metal complexes of terpyridines with polyfluorocarbon tails
(2023) Nößler, Maite; Neuman, Nicolás I.; Böser, Lisa; Jäger, René; Singha Hazari, Arijit; Hunger, David; Pan, Yixian; Lücke, Clemens; Bens, Tobias; Slageren, Joris van; Sarkar, Biprajit
In coordination chemistry and materials science, terpyridine ligands are of great interest, due to their ability to form stable complexes with a broad range of transition metal ions. We report three terpyridine ligands containing different perfluorocarbon (PFC) tails on the backbone and the corresponding FeII and CoII complexes. The CoII complexes display spin crossover close to ambient temperature, and the nature of this spin transition is influenced by the length of the PFC tail on the ligand backbone. The electrochemical properties of the metal complexes were investigated with cyclic voltammetry revealing one oxidation and several reduction processes. The fluorine-specific interactions were investigated by EPR measurements. Analysis of the EPR spectra of the complexes as microcrystalline powders and in solution reveals exchange-narrowed spectra without resolved hyperfine splittings arising from the 59Co nucleus; this suggests complex aggregation in solution mediated by interactions of the PFC tails. Interestingly, addition of perfluoro-octanol in different ratios to the acetonitrile solution of the sample resulted in the disruption of the Furn:x-wiley:09476539:media:chem202301246:chem202301246-math-0001 F interactions of the tails. To the best of our knowledge, this is the first investigation of fluorine-specific interactions in metal complexes through EPR spectroscopy, as exemplified by exchange narrowing.