Structural Criteria for the Design of Anion Receptors:  The Interaction of Halides with Electron-Deficient Arenes

Abstract

This paper refines the nature of the interactions between electron-deficient arenes and halide anions. Conclusions are based on (i) new crystal structures containing alkali halide salts with 1,2,4,5-tetracyanobenzene (TCB) and 18-crown-6, (ii) evaluation of crystal structures found in the Cambridge Structural Database, and (iii) MP2/aug-cc-pVDZ calculations of F-, Cl-, and Br- complexes with TCB, 1,3,5-tricyanobenzene, triazine, and hexafluorobenzene. When the halide lies above the plane of the π system, the results establish that three distinctly different types of complexes are possible: strongly covalent σ complexes, weakly covalent donor−π-acceptor complexes, and noncovalent anion−π complexes. When aryl C−H groups are present, a fourth type of interaction leads to C−H · · · X- hydrogen bonding. Characterization of the different geometries encountered with the four possible binding motifs provides criteria needed to design host architectures containing electron-deficient arenes.

Molecular Complexes of Simple Anions with Electron‐Deficient Arenes: Spectroscopic Evidence for Two Types of Structural Motifs for Anion–Arene Interactions

“…This off-center geometry, which has been interpreted as a weak s motif, appears to be the preferred binding mode for the interaction of Br À with strongly electron-deficient aromatic rings. [6,9,40,41] This structural feature also characterizes the TNB-Br À complex (6) with an elongated CÀBr bond of 2.67 .…”

“…[38,39] Insights into the structural features of the anion interaction with an aromatic ring in an isolated state have been obtained in recent theoretical work. [6,[40][41][42][43][44][45][46][47] Besides covalent bonding, noncovalent interactions have also been recognized. [6,44,48,49] Indeed, a variety of different complexes with different binding motifs are found, depending on the nature of the substituents on the aromatic or heteroaromatic ring and the nature of the anion, which have been classified as delivering: 1) strongly covalent s adducts (Meisenheimer complexes), 2) weakly covalent donor-p-acceptor complexes, and 3) noncovalent anion-p complexes.…”

“…[6,44,48,49] Indeed, a variety of different complexes with different binding motifs are found, depending on the nature of the substituents on the aromatic or heteroaromatic ring and the nature of the anion, which have been classified as delivering: 1) strongly covalent s adducts (Meisenheimer complexes), 2) weakly covalent donor-p-acceptor complexes, and 3) noncovalent anion-p complexes. [40,41] Furthermore, whenever feasible, complexes bound by hydrogen bonds also have to be taken into account. To identify the prevailing binding motif in an isolated complex, mass spectrometric means alone may not be adequate.…”

Functional molecules and materials by π‐Interaction based quantum theoretical design

“…An anion can interact with a p system through hydrogen bonding, noncovalent anion-p interactions and covalent r interactions. [59] For instance, chloride and azide anions interact with p system of striazine and trifluorotriazine molecules (anion-p interaction) while fluoride forms a covalent bond with an aryl carbon of these molecules (via covalent r interaction). [16] Interaction of simple anions with p electronic cloud of aromatics is enthalpically less favorable than that with aryl hydrogens.…”

Rapid insight into C60 influence on biological functions of proteins

“…These binding forces have been defined between negatively charged species and electron-deficient aromatic rings [93,94]. The C 60 -protein complexes presented herein, reveal high number of glutamic acid and aspartic acid residues in observed binding sites (~14% of all residues), and additionally, glutamic acid is the most numerous amino acid residue of all (see Fig.…”