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The cohesive energy of a-fluorine, with C2/c space group symmetry, was calculated at benchmark quality by applying the method of increments. The known experimental X-ray structure data needed to be refined, since the reported intramolecular bond length was unrealistically large. At the CCSD(T) level,i ncluding corrections for zero-point energy, the basis set superposition error,a nd extrapolatedt ot he complete basis set limit, ac ohesive energy of À8.72 kJ mol À1 was calculated, whicha grees well with the 0K-extrapolated experimental value of À8.35 kJ mol À1 . [1] Comparisono ft he C2/c structure with a Cmca structure, isotypic to that of chlorine, bromine, and iodine reveals that the origin of the different structure of solidf luorine, compared to the heavier halogens,i st he lack of significantly stabilizing s-hole interactions.I na ddition, the wave numberso ft he stretching mode in solid fluorine werec alculated at coupled cluster level and compared to newly recorded Raman spectra of condensed fluorine. Both experiment and calculation indicate as light up-shiftf or the stretching mode by 2o r5cm À1 , respectively,w ith respect to af ree F 2 molecule in the gas phase.

We employ density functional theory with Hubbard U correction or hybrid functionals to study the series of magnetic 3d metal trifluorides MF 3 (M = Ti-Ni). Experimental lattice parameters are reproduced with an error margin of 0.5%-4.3%. Cooperative Jahn-Teller distortions are reproduced for MnF 3 , but also found in TiF 3 and CoF 3 at smaller levels compared to MnF 3 . Trends in electronic structure with respect to positions of the d bands are linked to the magnetic properties where M = Ti-Cr are weak magnetic Mott-Hubbard insulators, M = Fe-Ni are strong magnetic charge-transfer insulators and MnF 3 falls in between. Our work contributes to the characterization of the relatively unknown NiF 3 , since FeF 3 and CoF 3 have similar electronic and magnetic properties. However, NiF 3 does not show a Jahn-Teller distortion as present in CoF 3 .

The Simons process, otherwise known as the electrochemical fluorination (ECF) method, is widely used in industry to electrolytically synthesize chemicals for various purposes. Even to this day, the exact mechanism of the ECF reaction remains unknown, but is believed to involve the formation of an anodic nickel fluoride film with highly oxidized nickel centers. In this study, experiments and density functional theory calculations are combined to characterize the initial anodic peak occurring at potentials typically required in an ECF cell. NiF2 is believed to form a passivating layer at low potentials. The calculations show that a potential of +3.1 V is required to oxidize surface Ni2+ centers to Ni3+. This is in good agreement with the measured anodic peak at +3.57 V.

Anhydrous hydrogen fluoride (HF) is electrochemically activated on Ni electrodes in the Simons process. We study the electrode/electrolyte interface using DFT methods and find the splitting of HF to be exothermic even at low cell potentials.

Electrochemical fluorination in anhydrous HF, also known as the Simons process, is a widely used industrial method for fluorination of organic compounds. Its mechanism, being not so well understood, has long been debated and is believed to involve higher valent nickel fluorides formed on the nickel-plated anode during the process. One of these is speculated to be Ni2F5, which was previously reported in the literature and assigned via infrared spectroscopy, but its crystal structure is not yet known. We have identified known crystal structures of compounds with similar stoichiometries as Ni2F5 and utilized them as a starting point for our periodic DFT investigations, applying the PBE+U method. Ni2F5 as the most stable polymorph was found to be of the same crystal structure as another mixed valent fluoride, Cr2F5. The calculated lattice parameters are a = 7.24 Å, b = 7.40 Å, c = 7.08 Å and β = 118.9° with an antiferromagnetic ordering of the nickel magnetic moments.

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