Synergistic and diminutive effects between triel bond and regium bond: Attractive interactions between π‐hole and σ‐hole

Abstract

High quantum chemical calculations have been performed for binary complexes of MCN···ZX3 (M = Cu, Ag, Au; Z = B, Al; X = H, F) and C2H4···AlX3. The strength of triel bonding depends on the nature of triel and coin metal atoms as well as the F substituents and electron donors. The molecular electrostatic potential (MEP) analysis confirms a σ‐hole at the M‐C bond end of MCN, engaging in a regium bond with C2H4 in an increasing sequence of AgCN < CuCN < AuCN. The complex C2(CN)4···AuCN is unstable in view of MEPs, but a big attractive interaction energy (−38 kcal/mol) is produced when both molecules approach, which is mainly caused by polarization including orbital interactions. Both types of interactions are strengthened in ternary complex of C2H4···MCN···ZX3 but are weakened in NCAu···C2H4···AlX3 and C2(CN)4···AuCN···ZH3. It is found that the variation from synergistic to diminutive effects can be modulated by four CN groups in C2(CN)4. Interestingly, the binding distances of both interactions have an unexpected change. The cooperativity of both interactions has been explained with MEP and charge transfer. When C2H4 binds with AlX3 or AuCN, its π electron density is greatly decreased and even its MEP becomes positive, but it is still able to participate in a regium bond or a triel bond.

Not Only Hydrogen Bonds: Other Noncovalent Interactions

“…Au(I)) the more acidic the Lewis acid; see, for instance, the complex (CF3)3Au•••pyridine [63]. We cited Legon in a 2014 paper [64] In 2019, several papers were published on regium bonds, from which we have selected the following four Reference works [65][66][67][68].…”

“…The binding energies for regium bonds complexes range between -24 and -180 kJ•mol -1 , whereas those of the HB complexes are between -6 and -19 kJ•mol -1 [65]. Similarly, triel and regium bonds were compared, in particular they augmentative and diminutive interactions; the calculations were carried out at second order Møller-Plesset (MP2) perturbation theory [66]. For Cu, Ag, and Au atoms, the aug-cc-pVDZ-PP pseudopotential was used to account for relativistic effects.…”

“…Figure 5 shows the self-assembled dimer that is formed in the solid state of trichlorido-(1-hexylcytosine)gold(III) where two symmetrically equivalent Au•••Cl regium bonds are established. In 2019, several papers were published on regium bonds, from which we have selected the following four Reference works [65][66][67][68].…”

Competition between Intra and Intermolecular Triel Bonds. Complexes between Naphthalene Derivatives and Neutral or Anionic Lewis Bases

“…There are also exceptional cases wherein a tetravalent Tr atom can generate a σ-hole [57]. This TrB has generated sufficient interest so as to be the focus of a number of prior quantum chemical studies [58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73]. Our own earlier study of the TrB [73] in complexes of TrR 3 (Tr = B, Al, Ga; R = H, F, Cl, Br, CH 3 ) with pyrazine provides some information about the influence of various substituents on the energy, geometry, and properties of this interaction.…”

“…Consistant with the aforementioned findings of a poor relationship between binding energy and π-hole intensity, there was little correlation observed here between the electron-withdrawing power of the substituent attached to the Lewis acid and the binding energy. The cooperativity involved in TrBs has been explored, combined with the halogen bond [74], anion-π interactions [58] or the regium bond [68].…”