The complex [CpFe(dppf)(CO)][B(Ar F ) 4 ] [1][B-(Ar F ) 4 ] (Cp = cyclopentadienyl, dppf = 1,1′-bis-(diphenylphosphino)ferrocene, and [B(Ar F ) 4 ] − = tetrakis[3,5bis(trifluoromethyl)phenyl]borate) was made by removal of one carbonyl ligand from the dicarbonyl complex [CpFe(CO) 2 (κ 1dppf)]I and exchange of the I − for [B(Ar F ) 4 ] − that allowed for electrochemical investigations. The cyclic voltammogram of [1] + showed a reversible anodic process due to oxidation of the ferrocenediyl moiety of the dppf ligand. A quasi-reversible cathodic process was also observed, and this reduction occurred at the CpFe moiety, as determined by variable-temperature (+22 and −30 °C) IR spectroelectrochemistry (SEC) and further supported by DFT calculations. This reduction event resulted in the formation of the two possible dimers [Cp 2 Fe 2 (μ-CO) 2 (μ-dppf)] and [Cp 2 Fe 2 (CO) 2 (μ-dppf)] along with deligation of one dppf ligand.

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).