Anion-π interaction with alkenes: persistent complexes irreversible reactions of anions with tetracyanoethylene.

The interaction of the tetracyanoethylene (TCNE) π-acceptor with oxo- and fluoro-anions (BF, PF, ClO, NO) led to the formation of anion-π complexes in which these polyatomic anions were located over the face of alkenes, with multiple contacts being shorter than the van der Waals separations. The anion-π associations of TCNE with halides were delimited by the electron-donor strengths and nucleophilicity of the anions. Specifically, while bromides formed persistent anion-π associations with TCNE in the solid state and in solutions, only transient anion-π complexes with iodides and chlorides were observed.

Halogen Bonding and/or Covalent Bond: Analogy of 3c-4e N···I···X (X = Cl, Br, I, and N) Interactions in Neutral, Cationic, and Anionic Complexes.

X-ray structural measurements and computational analysis demonstrated the similarity of the geometries and electronic structures of the X-I···N (X = Cl, Br, I, and N) bonding in strong halogen-bonded (HaB) complexes and in the anionic or cationic halonium ions. In particular, I···N bond lengths in the solid-state associations formed by strong HaB donors (, I, IBr, ICl, and -iodosuccinimide) and acceptors (, quinuclidine or pyridines) were in the same range of 2.3 ± 0.

Exploring the Nature of Anion-π Interactions: Complexes of π-Acceptors with Fluoro- or Oxoanions Compared to the Associations with Halides.

The variations in the nature and properties of the anion-π complexes with different types of anions are identified via experimental (UV-vis and X-ray crystallographic) measurements and computational analysis of the associations of tetracyanopyrazine, tetrafluoro-, or dichlorodicyano--benzoquinone. Co-crystals of these π-acceptors with the salts of fluoro- and oxoanions (PF, BF, CFSO, or ClO) comprised anion-π bonded alternating chains or 1:2 complexes showing interatomic contacts of up to 15% shorter than the van der Waals separations. DFT computations confirmed that binding energies between the neutral π-acceptors and polyatomic noncoordinating oxo- and fluoroanions are comparable to those in the previously reported anion-π complexes with more nucleophilic halides.