Halide Recognition through Diagnostic “Anion–π” Interactions: Molecular Complexes of Cl⁻, Br⁻, and I⁻ with Olefinic and Aromatic π Receptors

Abstract

Intense colorations and new charge‐transfer absorption bands are observed upon addition of a halide (Cl−, Br−, I−) to neutral organic π acceptors with electron‐deficient olefinic and aromatic centers. These phenomena results from noncovalent anion–π interactions (shown schematically), which were confirmed by X‐ray crystallography.

“Caging” Anions through Crystal Engineering to Avoid Polymerization: Structural, Conformational and Theoretical Investigations of New Halocadmate [Cd2X7]3– Anions (X = Cl/Br)

“…The results were similar for both of the anions; in vacuo, the molecules assume a near linear geometry around the bridging atom with a Cd-X-Cd angle of 165. 15 3-, respectively. However, when the calculations were carried out in a simulated aqueous environment, the calculated conformations become comparable to those found in the crystals, as shown in Figure 6 where the optimized geometry of [Cd 2 Cl 7 ] 3-is reported together with the bond lengths and angles obtained for [Cd 2 Br 7 ] 3-(bottom values).…”

“…In both of the structures, each anion is surrounded at a maximum distance of 4 Å by eight Co III complexes that form a cage that prevents any close contact with the other anions and thus inhibits the formation of polymeric chains ( Figures 3 and 4 for 1 and 2, respectively). Besides the electrostatic forces of attraction, the intermolecular interactions that hold the cations and anions together in both crystal structures are of the type C-H···Cl/Br, π-π stacking, C-H···π and anion···π interactions [15] ( Figures S4 and S5, Supporting Information). In addition, the cocrystallized water molecules contribute to the packing robustness that is involved in O-H···O as well as C-H···O hydrogen bonds.…”

Anion–π, Lone‐Pair–π, π–π and Hydrogen‐Bonding Interactions in a CuIIComplex of 2‐Picolinate and Protonated 4,4′‐Bipyridine: Crystal Structure and Theoretical Studies

“…[7] Some experimental and extensive theoretical studies have confirmed that π-acidic systems as diverse as halo-, [8] nitro-and cyanosubstituted benzenes, [9] calixarenes, [10] cyanuric acids, [11] tetrazines [12] and triazines [13] can interact with simple anions such as halides or more charge delocalised multiatomic anions such as NO 3 -, ClO 4 -and BF 4 -as well as with neutral lone-pair donor atoms such as nitrogen and oxygen. If anion-π or lone-pair-π interactions are to be exploited in synthetic anion receptors, it is necessary to design systems incorporating sufficient π-acidity.…”

Versatile Anion–π Interactions between Halides and a Conformationally Rigid Bis(tetraoxacalix[2]arene[2]triazine) Cage and Their Directing Effect on Molecular Assembly

“…[3,5] Indeed, a recent report indicated that the noncovalent anion-p interaction contributes less significantly to the formation of chloride-p-C 6 F n H 6Àn complex. [6] Heteroatom-bridged calixaromatics are an emerging type of novel macrocyclic molecules and they exhibit unique and versatile structural and molecular recognition properties.…”