Tris(pentafluorophenyl)phosphine
molecules in a new phase pack
to form hourglass-shaped one-dimensional channels, whose inner surface
is occupied by only fluorine. The channels show an effective diameter
of 3.80 Å at the belly and only 2.68 Å at the neck, neither
being possible for the encapsulation of any solvent molecules or for
the permeability of air (N2 and O2), thus demonstrating
an absolute vacuum. Such “vacuum” channels in the crystals
have never been reported and would be of great significance in photo-
and electrophysics. In addition, the structural analysis indicated
that F···F contacts and F···π
interactions are mainly responsible for the specific packing in the
new phase, and a σ-hole-type attraction is found in both F···F
and F···π forces according to the DFT computations.
Successive structural transformations were observed in the methanolic solution containing 4-iodo-1-methylpyridin-1-ium iodide (IPyMe·I) and bismuth iodide (BiI3). When kept in the solution, the amorphous solid (P_1) obtained immediately at mixing...
Based on the DFT‐level‐calculated molecular volume (Vmol) of pyrrole and its liquid density, pyrrole manifests the highest liquid density coefficient LDc (defined as [Vmol×density ×0.6023]/FW) value of 0.7. Normal liquids have LDc <0.63. This very high LDc is due to the strong N−H⋅⋅⋅π interactions in solution, and hence pyrrole can be considered to be a pseudo‐crystalline liquid. When trapped inside the confined space of a crystalline sponge, a reorientation of the N−H⋅⋅⋅π interaction is observed leading to specific cyclic N−H⋅⋅⋅π tetramers and N−H⋅⋅⋅π dimers, as verified by single‐crystal X‐ray crystallographic and computational methods. These tetramers are of the same size as four pyrrole molecules in the solid‐state of pyrrole, yet the cyclic N−H⋅⋅⋅π intermolecular interactions are circularly oriented instead of being in the linear zigzag structure found in the X‐ray structure of a solid pyrrole. The confinement thus acts as an external driving force for tetramer formation.
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