Octafluorocubane radical anion – where does the extra electron sit?
Derek Lowe reports the story[cite]10.1126/science.abq0516[/cite] that the recently synthesized octafluorocubane can absorb one electron to form a radical anion – an electron in a cube. So I thought it would be fun to compute exactly where that electron sits!
A ωB97XD/Def2-TZVPPD/SCRF=chloroform calculation (DOI: 10.14469/hpc/11090) is carried out on the neutral system (optimizing its geometry) and then the radical anion at the same geometry. Cubes of total electron density are evaluated for both and then the neutral form is subtracted from the anion. The result is shown below (density isosurface value 0.0025 au; click on the image to load a rotatable 3D model of the density difference).
The below is at the optimised anion geometry for both species;
The colour code is that blue represents the location of the additional electron, and red indicates reduced electron density compared to the anion. Arrow 1 shows an additional sphere of density inside the cube – yes, an electron in a cube. But you probably would not have anticipated that the outer surface of the cube (arrow 2) is also surrounded by that electron and there is a reduced density layer on the inside surface of the cube. The C-F bonds have regions of both additional density and reduced density.
Postscript: Perfluorododecahedrane added as per comment
Postscript: Perfluorotetrahedrane added for completeness
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