Substituent Effects on the Binding of Halides by Neutral and Dicationic Bis(triazolium) Receptors

Abstract

The effects of substituent and overall charge upon the binding of a halide anion by a bis(triazolium) receptor are studied by M06-2X DFT calculations, with the aug-cc-pVDZ basis set. Comparison is also made between a receptor that engages in H-bonds, with a halogen-bonding species. Fluoride is clearly most strongly bound, followed by Cl(-), Br(-), and I(-) in that order. The dicationic receptor engages in stronger complexes, but not by a very wide margin compared to its neutral counterpart. The binding is enhanced as the substituent on the two triazolium rings becomes progressively more electron-withdrawing. Halogen-substituted receptors, whether neutral or cationic, display a greater sensitivity to substituent than do their H-bonding counterparts. Both Coulombic and charge transfer factors obey the latter trends but do not correctly reproduce the stronger halogen vs hydrogen bonding. Both H-bonds and halogen bonds are nearly linear within the complexes, due in part to bond rotations within the receptor that bring the two triazole rings closer to coplanarity with the central benzene ring.

Highly Selective Halide Receptors Based on Chalcogen, Pnicogen, and Tetrel Bonds

“…[68,69] This basis set and functional have been applied previously to similar sorts of systems to good effect. [14,[33][34][35][70][71][72][73][74][75] Relativistic effects are expected to be most significant for atoms below the third row of the periodic table. Minima on each potential energy surface were assured by the absence of any negative frequencies.…”

“…This group later [30] appliedIhalogen bonds to develop preorganized multidentate receptors capable of high-affinity anion recognition.H uber's group compared [31] entropic with enthalpic contributions to such binding. Thiss ame fluoride preference was shown [34] by as eries of charged bis-(triazolium) receptors, on which electron-withdrawings ubstituents have ag reater influencef or halogen-bonding receptors than they do for H-bonding counterparts. [32] Our own group has engaged in severalr ecent studies in this arena,w here our quantum calculations have compared halogen with hydrogen-bonded receptors.R eplacemento ft he Hbondingp rotons of bis-triazole-pyridine by halogen atoms [33] demonstratedt hat Is ubstitution yields the greatest binding enhancementw ith various halides.…”

Strong and Selective Halide Anion Binding by Neutral Halogen‐Bonding [2]Rotaxanes in Wet Organic Solvents

“…Both rotaxanes 1.XB 2 and 2.XB 2 were found to bind anions following the selectivity trend SO 4 2À > Cl À > Br À > I À ,i no rder of decreasing charged ensity and basicity (Table 1). For rotaxane 1.XB 2 ,t he convergent halogen-bonding interactionsa rising from the meta-positioned iodotriazole units on the macrocycle benzene spacer,a sp redicted computationally, [52] resulted in all anionsb eing bound very strongly with 1:1h ost-guest binding stoichiometry.T hiss uggestsr otaxane 1.XB 2 binds anions through an induced-fit mode, by which the axle and macrocycle components can adjust their positions relative to each other to accommodate anion-guest size variation. The importance of the relative positions of the iodotriazole motifs on the macrocycle can be seen by comparing the binding properties of rotaxanes 1.XB 2 and 2.XB 2 ,w hich reveal several notable differences (Table 1).…”

Ion‐Pair Halogen Bonds in 2‐Halo‐Functionalized Imidazolium Chloride Receptors: Substituent and Solvent Effects

“…Previous calculations on related ion-pair XBs often employ the M06-2X functional, [34][35][36][37]56] which performsw ell for traditional (i.e.,n on-ion-pair) XBs [57] and interactions involving anionic electron donors. [58] On the other hand, B3LYP is undoubtedly one of the most popularf unctionals and has been used in several theoretical studies, [55,59] including ion-pair XBs.…”