Cooperative interaction between π-hole and single-electron σ-hole interactions in O2S···NCX···CH3 and O2Se···NCX···CH3 complexes (X = F,Cl, Br and I)

Ab initio calculations are performed to analyse the cooperative effects between π-hole and single-electron σ-hole interactions in O₂S···NCX···CH₃ and O₂Se···NCX···CH₃ complexes, where X = F, Cl, Br and I. These effects are investigated in terms of geometric and energetic features of the complexes, which are computed by UMP2/aug-cc-pVTZ(-PP) method. Our results indicate that the shortening of the each π-hole bond distance in the complexes is dependent on the strength of the σ-hole interaction. The maximum and minimum energetic cooperativity values correspond to the most and least stable complexes studied in the present work. The cooperativity between both types of interaction is chiefly caused by the electrostatic effects. The topological analysis, based on the quantum theory of atoms in molecules, is used to characterise the interactions and analyse their enhancement with varying electron density at bond critical points.     

Cooperativity effects between σ-hole interactions: a theoretical evidence for mutual influence between chalcogen bond and halogen bond interactions in F2S···NCX···NCY complexes (X = F,Cl, Br,I; Y = H,F, OH)

Quantum chemical calculations are performed to study the cooperativity effects between chalcogen bond and halogen bond interactions in F₂S···NCX···NCY complexes, where X = F, Cl, Br, I and Y = H, F, OH. These effects are investigated in terms of geometric and energetic features of the complexes, which are computed by second-order Møller–Plesset perturbation theory (MP2). For each F₂S···NCX···NCY complex studied, the effect of cooperativity on the chalcogen bond is dependent on the strength of halogen bond. The results indicate that the interaction energies of chalcogen and halogen bonds in the triads are more negative relative to the respective dyads. The interaction energy of chalcogen bond is increased by 31%–49%, whereas that of halogen bond by 28%–62%. The energy decomposition analysis reveals that electrostatic force plays a main role in the cooperativity effects between the chalcogen bond and halogen bond interactions. The topological analysis, based on the quantum theory of atoms in molecules, is used to characterise the interactions and analyse their enhancement with varying electron density at bond critical points.     

Strengthening of the halogen-bonding by an aerogen bond interaction: substitution and cooperative effects in O3Z···NCX···NCY (Z = Ar,Kr, Xe; X = Cl,Br, I; Y = H,F, OH) complexes

The geometry, interaction energy and bonding properties of ternary complexes O₃Z···NCX···NCY (Z= Ar, Kr, Xe; X = Cl, Br, I and Y = H, F, OH) are investigated with ab initio calculations at the MP2/aug-cc-pVTZ level. Two different types of intermolecular interactions are present in these complexes, namely, aerogen bond (Z···N) and halogen bond (X···N). The formation mechanism and bonding properties of these complexes are analysed with molecular electrostatic potentials, quantum theory of atoms in molecules and non-covalent interaction index. It is found that the cooperativity energies in the ternary complexes are all negative; that is, the interaction energy of the ternary complex is greater (more negative) than the sum of the interaction energies of the corresponding binary systems. Also, the cooperativity energies increase with the increase of the interaction energies. The cooperative effects in the ternary complexes make a decrease in the total spin–spin coupling constants across the aerogen bonding, J(Z–N), which can be regarded as a proof for the reinforce of Z···N interactions in the ternary complexes with respect to the binary systems.     

Interplay and competition between the lithium bonding and halogen bonding: R3C···XCN···LiCN and R3C···LiCN···XCN as a working model (R = H,CH3; X = Cl,Br)

UMP2 calculations with aug-cc-pVDZ basis set were used to analyse intermolecular interactions in R₃C···XCN···LiCN and R₃C···LiCN···XCN triads (R = H, CH₃; X = Cl, Br) which are connected via lithium bond and halogen bond. To understand the properties of the systems better, the corresponding dyads are also studied. Molecular geometries and binding energies of dyads, and triads are investigated at the UMP2/aug-cc-pVDZ computational level. Particular attention is paid to parameters such as cooperative energies, and many-body interaction energies. All studied complexes, with the simultaneous presence of a lithium bond and a halogen bond, show cooperativity with energy values ranging between ?1.20 and ?7.71 kJ mol^?1. A linear correlation was found between the interaction energies and magnitude of the product of most positive and negative electrostatic potentials (V_S,maxV_S,min). The electronic properties of the complexes are analysed using parameters derived from the atoms in molecules (AIM) methodology. According to energy decomposition analysis, it is revealed that the electrostatic interactions are the major source of the attraction in the title complexes.     

Tuning of tetrel bonds interactions by substitution and cooperative effects in XH3Si···NCH···HM (X = H,F, Cl,Br; M = Li,Na, BeH and MgH) complexes

In this work, the interplay between the tetrel bond and the dihydrogen bond is investigated in ternary XH₃Si···NCH···HM complexes, where X = H, F, Cl, Br and M = Li, Na, BeH, MgH. The nature of Si···N and H···H interactions is studied by molecular electrostatic potential (MEP), noncovalent interaction and electron localisation function analyses. All binding distances in the ternary complexes are shorter than those of isolated XH₃Si···NCH and NCH···HM systems. That is, the two types of interactions have a cooperative effect on each other. The results of the MEP analysis indicate that the enhancement of the Si···N and H···H bonds can mainly be attributed to the electrostatic interaction. The plot of the reduced density gradient versus sign (λ₂)ρ indicates that the location of the spike associated with each interaction in the ternary systems moves slightly towards the negative (λ₂)ρ values with respect to the binary systems. This confirms that both Si···N and H···H interactions in the ternary complexes are strengthened by the presence of other. Besides, cooperative effects lead to a considerable change in the ¹⁴N nuclear quadrupole coupling constant values of the ternary complexes relative to the XH₃Si···NCH complexes.     

Cooperative effects between F … Ag bonded and X … Br (Cl) halogen-bonded interaction in BrF(ClF) … AgX … BrF(ClF) (X = F,Cl, Br) complexes: a theoretical study

The equilibrium structures, interaction energies and binding properties of ternary BrF(ClF)?… AgX?…?BrF(ClF)(X?=?F, Cl, Br) complexes and the corresponding binary systems have been studied by DFT method at the X3LYP/aug-cc-pVQZ level. Cooperative effects are probed by analysing charge transfer, electronic properties and orbital interactions when F?…?Ag bond and X?…?Br (Cl) halogen bond coexist in the same complex. The results indicate that the X?…?Br (Cl) halogen bond has a greater enhancing effect than the F?…?Ag bond does, resulting in a shorter binding distances, larger interaction energies and greater electron densities for the ternary complexes than for the corresponding binary ones. In addition, the origins of both the F?…?Ag bond and X?…?Br (Cl) halogen bond have been deduced via energy decomposition.     

Cooperativity between the hydrogen bonding and halogen bonding in F3CX ··· NCH(CNH) ··· NCH(CNH) complexes (X=Cl,Br)

MP2 calculations with the cc-pVTZ basis set were used to analyse the intermolecular interactions in F₃CX?···?NCH(CNH)?···?NCH(CNH) triads (X=Cl, Br), which are connected via hydrogen and halogen bonds. Molecular geometries, binding energies, and infrared spectra of the dyads and triads were investigated at the MP2/cc-pVTZ computational level. Particular attention was given to parameters such as the cooperative energies, cooperative dipole moments, and many-body interaction energies. All studied complexes, with the simultaneous presence of a halogen bond and a hydrogen bond, show cooperativity with energy values ranging between ?1.32 and ?2.88?kJ?mol^?1. The electronic properties of the complexes were analysed using the Molecular Electrostatic Potential (MEP), electron density shift maps and the parameters derived from the Atoms in Molecules (AIM) methodology.