Understanding the anion–π interactions with tetraoxacalix[2]arene[2]triazine

Abstract

Anion-π interaction is a new type of non-covalent interaction. It has attracted growing interest in recent years both theoretically and experimentally. However, the nature of bonding between an anion and an electron-deficient aromatic system has remained elusive. To understand the bonding nature in depth, we have carried out a systematic computational study, using model systems that involve tetraoxacalix[2]arene[2]triazine 1, an electron-deficient macrocyclic host, and four anions, X(-) (X(-) = SCN(-), NO3(-), BF4(-), and PF6(-)), of varied sizes and shapes. The geometries for the 1·X(-) complexes were optimized using the extended ONIOM (XO) method. The good agreements with the X-ray experimental results provide a validation of our theoretical schemes. The nature of the non-covalent interactions was analyzed with the help of the AIM (atoms in molecules), RDG (reduced density gradient) and LMO-EDA (local molecular orbital-energy decomposition analysis) methods. The results clearly reveal the involvement of anion-π bonding, as well as a weak, yet significant, hydrogen bonding interaction between the benzene C-H on 1 and the anion of NO3(-) or PF6(-). The bonding energies of 1·X(-) were calculated with the XYG3 functional, and the results were compared with those from MP2, M06-2X and some other functionals with non-covalent interaction corrections (e.g., B3LYP-D3, and ωB97X-D). We conclude that the binding strengths follow the order of 1·NO3(-) > 1·SCN(-) > 1·BF4(-) > 1·PF6(-), where the difference between 1·SCN(-) and 1·BF4(-) is less significant. The strongest interaction in 1·NO3(-) comes from: (1) the effective electronic interaction between NO3(-) and the triazine rings on 1; and (2) the weak hydrogen bonding interaction between the benzene C-H on 1 and nitrate, which cooperates with the anion-π interactions.

The XYG3 type of doubly hybrid density functionals

“…There exist many benchmarking calculations, as well as practical applications, for the xDH functionals. The results have been intensively compared with those from other DFT methods and WFT methods.…”

“…In the followed sections, we will discuss the theoretical background of the DH functionals, briefly reviewing the adiabatic connection (AC) formalism, coordinate scaling relations, and Görling–Levy (GL) perturbation theory . General performance of the DH functionals will then be summarized, not only for energies, but also for structures. In particular, we will present the fractional charge behaviors of the DH functionals, examining the SIEs, the delocalization errors and the deviation from the linearity condition, as well as their effects on the predicted ionization potentials, electron affinities and fundamental gaps, providing a theoretical rationale for the observed good performance of the xDH functionals.…”

Theoretical Study on the Hydrogen Bonding Interactions in Paracetamol-Water Complexes

“…However, more technical tools are required to elucidate the nature of H-bond in PA-H 2 O complexes. The quantum theory of atoms in molecules (QTAIM) 27,28 , natural bond orbital (NBO) analysis 29 and the localized molecular orbital energy decomposition analysis (LMO-EDA) 30 methods meet this requirements since they have been proved to be very useful tools in understanding of H-bond [31][32][33][34][35][36] . Therefore, ab initio calculations combined with QTAIM, NBO and LMO-EDA approaches were performed to investigate the hydrogen bonding interactions in PA-H 2 O complexes.…”

New Insights into the Ion-Specific Behaviors and Design Strategies for Ion–π Interactions

“…Until now, both types of ion-π interactions have been ascribed to a combination of electrostatic effects and ion-induced polarization effects. 14,[19][20][21][22][23][24][39][40][41] Thus, the binding properties for both cation-π and anion-π interactions are expected to be similar. However, some significantly different behaviors have been reported between them both experimentally and theoretically.…”