Baoan Gong

Cooperativity between the halogen bond and the hydrogen bond in H3N...XY...HF complexes (X, Y=F, Cl, Br).

Ab initio calculations are used to provide information on H(3)N...XY...HF triads (X, Y=F, Cl, Br) each having a halogen bond and a hydrogen bond. The investigated triads include H(3)N...Br(2)-HF, H(3)N...Cl(2)...HF, H(3)N...BrCl...HF, H(3)N...BrF...HF, and H(3)N...ClF...HF. To understand the properties of the systems better, the corresponding dyads are also investigated. Molecular geometries, binding energies, and infrared spectra of monomers, dyads, and triads are studied at the MP2 level of theory with the 6-311++G(d,p) basis set. Because the primary aim of this study is to examine cooperative effects, particular attention is given to parameters such as cooperative energies, many-body interaction energies, and cooperativity factors. The cooperative energy ranges from -1.45 to -4.64 kcal mol(-1), the three-body interaction energy from -2.17 to -6.71 kcal mol(-1), and the cooperativity factor from 1.27 to 4.35. These results indicate significant cooperativity between the halogen and hydrogen bonds in these complexes. This cooperativity is much greater than that between hydrogen bonds. The effect of a halogen bond on a hydrogen bond is more pronounced than that of a hydrogen bond on a halogen bond.

Competition between hydrogen bond and halogen bond in complexes of formaldehyde with hypohalous acids

An ab initio study of the complexes formed by hypohalous acids (HOX, X = F, Cl and Br) with formaldehyde has been carried out at the MP2/aug-cc-pVTZ computational level. Two minima complexes are found, one with an H...O contact and the other one with an X...O contact. The former is more stable than the latter, and the strength difference between them decreases as the size of the X atom increases. The associated HO and XO bonds undergo a bond lengthening and red shift, whereas a blue shift was observed in the bond of the hypohalous acid not involved in the interaction. The interaction strength and properties in both complexes are analyzed with atoms in molecules (AIM) and natural bond orbital (NBO) theories. The energy decomposition analyses indicate that the contribution from the electrostatic interaction energy is larger in the hydrogen-bonded complexes than that in the halogen-bonded complexes.

Cooperativity between two types of hydrogen bond in H3C–HCN–HCN and H3C–HNC–HNC complexes

Hydrogen-bonded clusters, H(3)C-HCN, HCN-HCN, H(3)C-HCN-HCN, H(3)C-HNC, HNC-HNC, and H(3)C-HNC-HNC, have been studied by using ab initio calculations. The optimized structures, harmonic vibrational frequencies, and interaction energies are calculated at the MP2 level with aug-cc-pVTZ basis set. The cooperative effects in the properties of these complexes are investigated quantitatively. A cooperativity contribution of around 10% relative to the total interaction energy was found in the H(3)C-HCN-HCN complex. In the case of H(3)C-HNC-HNC complex, the cooperativity contribution is about 15%. The cooperativity contribution in the single-electron hydrogen bond is larger than that in the hydrogen bond of HCN-HCN and HNC-HNC complexes. NMR chemical shifts, charge transfers, and topological parameters also support such conclusions.

Cooperativity between the Dihydrogen Bond and the N···HC Hydrogen Bond in LiH-(HCN)n Complexes

The cooperativity between the dihydrogen bond and the NHC hydrogen bond in LiH-(HCN)(n) (n=2 and 3) complexes is investigated at the MP2 level of theory. The bond lengths, dipole moments, and energies are analyzed. It is demonstrated that synergetic effects are present in the complexes. The cooperativity contribution of the dihydrogen bond is smaller than that of the NHC hydrogen bond. The three-body energy in systems involving different types of hydrogen bonds is larger than that in the same hydrogen-bonded systems. NBO analyses indicate that orbital interaction, charge transfer, and bond polarization are mainly responsible for the cooperativity between the two types of hydrogen bonds.

A new unconventional halogen bond C-X...H-M between HCCX (X = Cl and Br) and HMH (M = Be and Mg): an ab initio study.

In this article, a new type of halogen‐bonded complex YCCX···HMY (X = Cl, Br; M = Be, Mg; Y = H, F, CH3) has been predicted and characterized at the MP2/aug‐cc‐pVTZ level. We named it as halogen‐hydride halogen bonding. In each YCCX···HMY complex, a halogen bond is formed between the positively charged X atom and the negatively charged H atom. This new kind of halogen bond has similar characteristics to the conventional halogen bond, such as the elongation of the CX bond and the red shift of the CX stretch frequency upon complexation. The interaction strength of this type of halogen bond is in a range of 3.34–10.52 kJ/mol, which is smaller than that of dihydrogen bond and conventional halogen bond. The nature of the electrostatic interaction in this type of halogen bond has also been unveiled by means of the natural bond orbital, atoms in molecules, and energy decomposition analyses.

Theoretical Study of the Interplay between Lithium Bond and Hydrogen Bond in Complexes Involved with HLi and HCN

The lithium- and hydrogen-bonded complex of HLi-NCH-NCH is studied with ab initio calculations. The optimized structure, vibrational frequencies, and binding energy are calculated at the MP2 level with 6-311++G(2d,2p) basis set. The interplay between lithium bonding and hydrogen bonding in the complex is investigated with these properties. The effect of lithium bonding on the properties of hydrogen bonding is larger than that of hydrogen bonding on the properties of lithium bonding. In the trimer, the binding energies are increased by about 19% and 61% for the lithium and hydrogen bonds, respectively. A big cooperative energy (-5.50 kcal mol(-1)) is observed in the complex. Both the charge transfer and induction effect due to the electrostatic interaction are responsible for the cooperativity in the trimer. The effect of HCN chain length on the lithium bonding has been considered. The natural bond orbital and atoms in molecules analyses indicate that the electrostatic force plays a main role in the lithium bonding. A many-body interaction analysis has also been performed for HLi-(NCH)(N) (N=2-5) systems.

Surprising enhancing effect of methyl group on the strength of O⋯XF and S⋯XF (X=Cl and Br) halogen bonds

The role of methyl group in H(2)O⋯XF and H(2)S⋯XF (X=Cl and Br) halogen-bonded complexes has been investigated with quantum chemical calculations. The halogen bond in the H(2)O⋯XF complexes is stronger than that in the H(2)S⋯XF complexes. However, the S⋯X halogen bond is stronger than the O⋯X one with the increase of methyl number. The result shows that the methyl group in the halogen acceptor has a positive contribution to the formation of halogen bond and there is a positive nonadditivity of methyl groups. Surprisingly, the methyl groups in dimethyl sulfide causes an increase of 150% for the interaction energy of S⋯Cl halogen bond. The natural bond orbital analyses have been performed to unveil the mechanism of the methyl group in the halogen bonding formation.

Theoretical study of halogen–hydride halogen bonds in F3CL ··· HM (L=Cl, Br; M=Li, BeH, MgH) complexes

Quantum chemical calculations have been performed on six halogen–hydride halogen bonded complexes with F3CCl or F3CBr as the halogen donor and metal hydride (HLi, HBeH and HMgH) as the halogen acceptor. At the MP2/6-311++G(d,p) level, the interaction strength spans from 2.62 to 17.68 kJ mol–1. The C–Cl and C–Br bonds are contracted. However, no evident blue shift accompanies this contraction. The H–Li bond is also contracted, but the H–He and H–Mg bonds are lengthened. However, a blue shift occurs for all these bond-stretching vibrations. These properties were analysed using the theory of natural bond orbital (NBO) and atoms in molecules (AIM). A symmetry-adapted perturbation theory (SAPT) analysis was also carried out to unveil the nature of this novel interaction. It is demonstrated that the electrostatic interaction plays a main role in the interaction, although induction and dispersion interactions are also important.

Large blue shift of the H–Ar stretching frequency in hydrogen- and halogen-bonded complexes of HArF with dihalogen molecules

Quantum chemical calculations have been performed on the complexes formed between HArF and dihalogen molecules (XY=ClCl, ClF, BrCl, and BrF) at the MP2/6-311++G(2d,2p) level. For each complex, two minima were found, which correspond to one hydrogen-bonded complex and one halogen-bonded complex. The halogen-bonded complex with the F atom of HArF is more stable than the hydrogen-bonded complex with the H atom of HArF. A large blue shift of the H-Ar stretching frequency was observed in the hydrogen-bonded complex. However, in the halogen-bonded complex, in which the H-Ar bond is not involved in the interaction, a much large blue shift was observed for the same bond. The natural bond orbital and atoms in molecules analyses have been performed for these complexes. The energy decomposition analysis indicated that the electrostatic interaction plays a main contribution in formation of both complexes although the contribution from the charge-transfer interaction is also important.

Enhancing the function, non-additivity, and substitution position effect of the Li atom in the cation–π interaction and its mechanism: an ab initio study of Li+ ··· Li-substituted benzene complexes

Quantum chemical calculations have been performed to study the cation–π interaction in the Li+ ··· C6H6– n Li n (n = 0–6) complex. The results show that the cation–π interaction is enhanced by lithium substitution in the aromatic ring. With increasing number of lithium substituents in the aromatic ring, the total interaction energy becomes more negative. However, the average contribution from one Li substituent to the interaction energy becomes smaller. The lithium substituent in the aromatic ring displays negative non-additivity in enhancing the cation–π interaction. The substitution position of the lithium substituent in the aromatic ring has a prominent effect on the strength of the cation–π interaction. The largest interaction energy (–97.7 kcal mol−1) is found for the Li+ ··· 1,3,5-C6H3Li3 complex. The enhancing effect of the Li atom can be understood in terms of the natural population analysis (NPA) charge on the carbon atom in the aromatic ring, the most negative electrostatic potential at the center of the aromatic ring, and energy decomposition.