Anion‐π Interaction: An Influential Force in Solid State Molecular Microstructures

Abstract

The crystal structures of simple triphenyl(pentafluorobenzyl)phosphonium salts provide crucial data on the influence of anion size on the molecular structure of bis(pentafluorobenzyl)phosphonium cations containing two adjacent electron‐deficient moieties. Whereas the bromide anions interact by anion‐π interaction in a 1:1 mode with the pentafluorobenzene unit Z‐configured, the bulkier anions iodide, tetrafluoroborate, and hexafluorophosphate result in a 1:2 tweezer‐like anti‐configuration in which one anion interacts simultaneously with two pentafluorobenzene units. When spatial separation of the two electron‐deficient rings match the size of the anion, anion‐π interactions induce a conformational change from the anti‐form observed for the smaller anion to the tweezer‐like syn‐form.

Anion−π Interactions with Fluoroarenes

“…Relevant Structural Parameters for the Anion−π Interactions As Observed in the Crystal Structures of 19−22 (in Å)123 …”

Nitrosyl–heme and anion–arene complexes: structure, reactivity and spectroscopy

“…In recent years, a notable amount of reports have described the anion π-interaction as a new binding motif. The interaction in a π-complex is weaker than in a σ-complex and difficult to ascertain in solution [32,33]. Conceivably, however, the anion approach to binding with a π-acidic system may span a continuity of motifs depending on the individual features of the anion and of the aromatic partner [34].…”

Towards design strategies for anion–π interactions in crystal engineering

“…The electron-deficient pentafluorophenyl (PFP) group is also a good building block for generating anion-π interactions. 64 Giese et al [80][81][82] have exploited this experimentally by focusing on purely organic salts where the positive charge is located some distance away from the PFP group. From their work it is evident that the position of an anion above the PFP π-system can be tuned.…”