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 F 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.

The hand in the cover depicts how spin‐crossover‐active CoII complexes are held together by noncovalent fluorine‐specific interactions between the perfluorinated alkyl chains on the ligand backbone. Once the hand releases the molecules into certain solvents, the fluorine‐specific interactions are broken up through preferential interactions with the solvent molecules, which are present in large excess. More information can be found in the Research Article by J. van Slageren, B. Sarkar and co‐workers (DOI: 10.1002/chem.202301246).

In recent years terpyridines (tpy) and mesoionic carbenes (MIC) have been widely used in metal complexes. With the right combination with a metal center, both of these ligands are individually known to generate excellent catalysts for CO 2 reduction. In this study, we combine the potentials of PFC (PFC = polyfluorocarbon) substituted tpy and MIC ligands within the same platform to obtain a new class of complexes, which we investigated with respect to their structural, electrochemical and UV/Vis/NIR spectroelectrochemical properties. We further show that the resulting metal complexes are potent electrocatalysts for CO 2 reduction in which CO is exclusively formed with a faradaic efficiency of 92 %. A preliminary mechanistic study, including the isolation and characterization of a key intermediate is also reported.