Lingpeng Meng

A comprehensive analysis of P···π pnicogen bonds: substitution effects and comparison with Br···π halogen bonds

Ab initio calculations were carried out in a systematic investigation of P···π pnicogen-bonded complexes XH2P···C2H2/C2H4 and FH2P···C2R2/C2R4 for X = H, CH3, OH, CN, Br, Cl, NO2, F, and R = F, CH3, as well as corresponding Br···π halogen-bonded complexes XBr···C2H2. Both the electron-withdrawing and electron-donating substituents in the electron acceptor have enhancing effects on the strength of P···π interactions. The electron-donating group in the electron donor leads to strengthening while the electron-withdrawing group leads to weakening of P···π interactions. The studied P···π and Br···π interactions are similar and are typically “closed-shell” non-covalent character in nature. Moreover, analyses of natural bond orbital and density difference of molecular formation indicated that charge transfer and polarization also play important roles in P···π interactions. The substituents have direct effects on the molecular electrostatic potential, and the charge transfer amount and extent of polarization of the P···π interaction are also specific to each substituent.

Insight into the nature of the interactions of furan and thiophene with hydrogen halides and lithium halides: ab initio and QTAIM studies

AbstractThe nature of the interactions of furan and thiophene with hydrogen halides and lithium halides has been investigated using ab initio calculations and QTAIM analysis. The concept of molecule formation density difference (MFDD) is introduced to study weak hydrogen bond (HB) and lithium bond (LB) interactions. The results have shown the molecular electrostatic potentials of furan and thiophene, as well as of the hydrogen halides and lithium halides, determine the geometries of the complexes. Both the studied HB and LB interactions can be classified as “closed-shell” weak interactions. The topological properties and energy properties at the bond critical points of HB and LB have been shown to be exponentially dependent on intermolecular distances d(H-bond) and d(Li-bond), which enables interpretation of the strength of the HB and LB interactions in terms of these ρ(r) properties. Electron transfer plays a more important role in the formation of HB than in that of LB, while electrostatic interaction in LB is more dominant than that in HB.Table of Contents (TOC) Image FigureThe idea of molecule formation density difference (MFDD) is used to study the weak interaction of hydrogen bond (HB) and lithium bond (LB).

Insight into the lithium/hydrogen bonding in (CH2)2X...LiY/HY (X: C=CH2, O, S; Y=F, Cl, Br) complexes

The nature of the lithium/hydrogen bonding between (CH2)2X(X: C=CH2, O, S) and LiY/HY(Y=F, Cl, Br) have been theoretically investigated at MP2/6-311++G (d, p) level, using Bader’s “atoms in molecules (AIM)” theory and Weinhold’s “natural bond orbital (NBO)” methodology. The molecule formation density differences (MFDD) of the titled complexes are analyzed. Two kinds of geometries of the lithium/hydrogen bonded complexes are compared. As a whole, the nature of lithium bond and hydrogen bond are different. For the same electron donor and the same acceptor, lithium bond is stronger than hydrogen bond. For the same electron acceptor and different kind of donors, the interaction energies follows the n-type> π-type > pseudo-π-type order. For the same (CH2)2X, the interaction energy increases in the sequence of Y=F, Cl and Br for lithium bond systems while it decreases for hydrogen bond systems. Electron transfer plays an important role in the formation of lithium bond systems while it is less important in the hydrogen bond systems.

Comparative studies on group III σ‐hole and π‐hole interactions

The σ‐hole of M2H6 (M = Al, Ga, In) and π‐hole of MH3 (M = Al, Ga, In) were discovered and analyzed, the bimolecular complexes M2H6···NH3 and MH3···N2P2F4 (M = Al, Ga, In) were constructed to carry out comparative studies on the group III σ‐hole interactions and π‐hole interactions. The two types of interactions are all partial‐covalent interactions; the π‐hole interactions are stronger than σ‐hole interactions. The electrostatic energy is the largest contribution for forming the σ‐hole and π‐hole interaction, the polarization energy is also an important factor to form the M···N interaction. The electrostatic energy contributions to the interaction energy of the σ‐hole interactions are somewhat greater than those of the π‐hole interactions. However, the polarization contributions for the π‐hole interactions are somewhat greater than those for the σ‐hole interactions.

The competition of Y⋯o and X⋯n halogen bonds to enhance the group V σ‐hole interaction in the NCY⋯oPH3⋯NCX and OPH3⋯NCX⋯NCY (X, YF, Cl, and Br) complexes

The positive electrostatic potentials (ESP) outside the σ‐hole along the extension of OP bond in OPH3 and the negative ESP outside the nitrogen atom along the extension of the CN bond in NCX could form the Group V σ‐hole interaction OPH3⋯NCX. In this work, the complexes NCY⋯OPH3⋯NCX and OPH3⋯NCX⋯NCY (X, YF, Cl, Br) were designed to investigate the enhancing effects of Y⋯O and X⋯N halogen bonds on the P⋯N Group V σ‐hole interaction. With the addition of Y⋯O halogen bond, the VS, max values outside the σ‐hole region of OPH3 becomes increasingly positive resulting in a stronger and more polarizable P⋯N interaction. With the addition of X⋯N halogen bond, the VS, min values outside the nitrogen atom of NCX becomes increasingly negative, also resulting in a stronger and more polarizable P⋯N interaction. The Y⋯O halogen bonds affect the σ‐hole region (decreased density region) outside the phosphorus atom more than the P⋯N internuclear region (increased density region outside the nitrogen atom), while it is contrary for the X⋯N halogen bonds.

Interplay between halogen bonds and hydrogen bonds in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes

AbstractThe character of the cooperativity between the HOX···OH/SH halogen bond (XB) and the Y―H···(H)OX hydrogen bond (HB) in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes has been investigated by means of second-order Møller−Plesset perturbation theory (MP2) calculations and “quantum theory of atoms in molecules” (QTAIM) studies. The geometries of the complexes have been determined from the most negative electrostatic potentials (VS,min) and the most positive electrostatic potentials (VS,max) on the electron density contours of the individual species. The greater the VS,max values of HY, the larger the interaction energies of halogen-bonded HOX···OH/SH in the termolecular complexes, indicating that the ability of cooperative effect of hydrogen bond on halogen bond are determined by VS,max of HY. The interaction energies, binding distances, infrared vibrational frequencies, and electron densities ρ at the BCPs of the hydrogen bonds and halogen bonds prove that there is positive cooperativity between these bonds. The potentiation of hydrogen bonds on halogen bonds is greater than that of halogen bonds on hydrogen bonds. QTAIM studies have shown that the halogen bonds and hydrogen bonds are closed-shell noncovalent interactions, and both have greater electrostatic character in the termolecular species compared with the bimolecular species. FigureThe character of the cooperativity between the X···O/S halogen bond (XB) and the Y―H···O hydrogen bond (HB) in OH/SH···HOX···HY (X=Cl, Br; Y=F, Cl, Br) complexes has been investigated by means of second-order Møller—Plesset perturbation theory (MP2) calculations and “quantum theory of atoms in molecules” (QTAIM) studies.

B3LYP calculations of the potential energy surfaces of the thermal dissociations and the triplet ground state of pyrolysis products XN(x̃3Σ−) for halogen azides XN3 (X: F, Cl, Br, I)

Abstract Mechanisms of XN 3 (X: F, Cl, Br, I) dissociations are proposed based on B3LYP calculated potential energy surfaces. The energy gaps between the ground-state reactants XN 3 ( x 1 A ′ ) and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, XN 3 ( x 1 A ′ )→ XN (a 1 Δ )+ N 2 ( x 1 Σ g + ) . The ISC point, therefore, is considered as a ‘transition state’ of the spin-forbidden reactions, XN 3 ( x 1 A ′ )→ XN ( x 3 Σ − )+ N 2 ( x 1 Σ g + ) . The methods of IRC and topological analysis of electron density are used to predict the thermal dissociation pathway of the reactions studied.

Substituent effects on the intramolecular hydrogen bond in 1-hydroxyanthraquinone: AIM and NBO analyses

The substituent effects on the intramolecular hydrogen bond in 1-hydroxyanthraquinone were investigated within the framework of the “atoms in molecules” theory and using “natural bond orbital” analysis. The calculated results show that introducing a substituent at the ortho- or meta-position has different effects: the substituents at ortho-position strengthen the intramolecular hydrogen bond, while the effects of the meta-position substituents are minor. Both ortho- and meta-position electron-donating substituents increase the covalent nature of the intramolecular hydrogen bond, whereas the meta-position electron-withdrawing substituents decrease it. Furthermore, striking parallels were found between the geometries, binding energies, and topological properties of the complexes studied. The topological properties of the bond critical point and ring critical point, the delocalization index DI(O, H), and the integrated properties of the interatomic surface δ(O, H) can all be treated as indicators to measure the strength of the intramolecular hydrogen bond.

Assessment of intermolecular interactions at three sites of the arylalkyne in phenylacetylene-containing lithium-bonded complexes: Ab initio and QTAIM studies†

The intermolecular interactions existing at three different sites between phenylacetylene and LiX (X = OH, NH2, F, Cl, Br, CN, NC) have been investigated by means of second‐order Møller−Plesset perturbation theory (MP2) calculations and quantum theory of “atoms in molecules” (QTAIM) studies. At each site, the lithium‐bonding interactions with electron‐withdrawing groups (F, Cl, Br, CN, NC) were found to be stronger than those with electron‐donating groups (OH and NH2). Molecular graphs of C6H5CCH···LiF and πC6H5CCH···LiF show the same connectional positions, and the electron densities at the lithium bond critical points (BCPs) of the πC6H5CCH···LiF complexes are distinctly higher than those of the σC6H5CCH···LiF complexes, indicating that the intermolecular interactions in the C6H5CCH···LiX complexes can be mainly attributed to the π‐type interaction. QTAIM studies have shown that these lithium‐bond interactions display the characteristics of “closed‐shell” noncovalent interactions, and the molecular formation density difference indicates that electron transfer plays an important role in the formation of the lithium bond. For each site, linear relationships have been found between the topological properties at the BCP (the electron density ρb, its Laplacian ∇2ρb, and the eigenvalue λ3 of the Hessian matrix) and the lithium bond length d(Li‐bond). The shorter the lithium bond length d(Li‐bond), the larger ρb, and the stronger the π···Li bond. The shorter d(Li‐bond), the larger ∇2ρb, and the greater the electrostatic character of the π···Li bond.

Discovery of σ-hole interactions involving ylides

The positive electrostatic potentials (σ-hole) have been found in ylides CH2XH3 (X = P, As, Sb) and CH2YH2 (Y = S, Se, Te), on the outer surfaces of group VA and VIA atoms, approximately along the extensions of the C–X and C–Y bonds, respectively. These electrostatic potentials suggest that the above ylides can interact with nucleophiles to form weak, directional noncovalent interactions similar to halogen bonding interactions. MP2 calculations have confirmed the formation of CH2XH3···HM complexes (X = P, As, Sb; M = BeH, ZnH, MgH, Li, Na). The interaction energies, interaction distances, topological properties (electron density and its Laplacian), and energy properties (kinetic electron energy density and potential electron energy density) at the X(1)···H(10) bond critical points are all correlated with the most negative electrostatic potential value of HM, indicating that electrostatic interactions play an important role in these weak X···H interactions. Similar to the halogen bonding interactions, weak interactions involving ylides may be significant in several areas such as organic synthesis, crystal engineering, and design of new materials.