Hai-Bei Li

Tetrel-hydride interaction between XH₃F (X = C, Si, Ge, Sn) and HM (M = Li, Na, BeH, MgH).

A tetrel-hydride interaction was predicted and characterized in the complexes of XH3F···HM (X = C, Si, Ge, Sn; M = Li, Na, BeH, MgH) at the MP2/aug-cc-pVTZ level, where XH3F and HM are treated as the Lewis acid and base, respectively. This new interaction was analyzed in terms of geometrical parameters, interaction energies, and spectroscopic characteristics of the complexes. The strength of the interaction is essentially related to the nature of X and M groups, with both the larger atomic number of X and the increased reactivity of M giving rise to a stronger tetrel-hydride interaction. The tetrel-hydride interaction exhibits similar substituent effects to that of dihydrogen bonds, where the electron-donating CH3 and Li groups in the metal hydride strengthen the binding interactions. NBO analyses demonstrate that both BD(H-M) → BD*(X-F) and BD(H-M) → BD*(X-H) orbital interactions play the stabilizing role in the formation of the complex XH3F···HM (X = C, Si, Ge, and Sn; M = Li, Na, BeH, and MgH). The major contribution to the total interaction energy is electrostatic energy for all of the complexes, even though the dispersion/polarization parts are nonnegligible for the weak/strong tetrel-hydride interaction, respectively.

Tetrel bond of pseudohalide anions with XH3F (X = C, Si, Ge, and Sn) and its role in SN2 reaction

The complexes of XH3F⋯N3-/OCN-/SCN- (X = C, Si, Ge, and Sn) have been investigated at the MP2/aug-cc-pVTZ(PP) level. The σ-hole of X atom in XH3F acts as a Lewis acid forming a tetrel bond with pseudohalide anions. Interaction energies of these complexes vary from -8 to -50 kcal/mol, mainly depending on the nature of X and pseudohalide anions. Charge transfer from N/O/S lone pair to X-F and X-H σ* orbitals results in the stabilization of these complexes, and the former orbital interaction is responsible for the large elongation of X-F bond length and the remarkable red shift of its stretch vibration. The tetrel bond in the complexes of XH3F (X = Si, Ge, and Sn) exhibits a significant degree of covalency with XH3F distorted significantly in these complexes. A breakdown of the individual forces involved attributes the stability of the interaction to mainly electrostatic energy, with a relatively large contribution from polarization. The transition state structures that connect the two minima for CH3Br⋯N3- complex have been localized and characterized. The energetic, geometrical, and topological parameters of the complexes were analyzed in the different stages of the SN2 reaction N3- + CH3Br → Br- + CH3N3.

Comparison of tetrel bonds and halogen bonds in complexes of DMSO with ZF3X (Z = C and Si; X = halogen)

A theoretical study of the complexes formed by dimethylsulfoxide (DMSO) with ZF3X (Z = C and Si; X = halogen) has been performed at the MP2/aug-cc-pVTZ level. Three local minima were found on the potential surface of complex DMSO–ZF3X, forming tetrel bonds and halogen bonds with O⋯Z and O⋯X contacts, respectively. The halogen-bonded complexes are more stable for CF3X than for SiF3X with an exception of CF4, on the contrary, the tetrel-bonded complexes DMSO–SiF3X are more stable than the analogues DMSO–CF3X. The strength of the tetrel bonds in DMSO–CF3X has a small dependence on the nature of the halogen atom, and DMSO–SiF3X has an abnormal dependence on it. Surprisingly, the tetrel bond in DMSO–SiF3X is stronger than that with an anion as the electron donor, exhibiting a partially covalent bond nature. A red shift was observed for the SO stretch vibration in most complexes, particularly in the tetrel-bonded complexes of DMSO–SiF3X. The Z–X stretch vibration exhibits a red shift in the tetrel bond but an irregular shift in the halogen bond.

Supramolecular interactions via hydrogen bonding contributing to citric-acid derived carbon dots with high quantum yield and sensitive photoluminescence

Herein, we report the characterization of highly fluorescent citric-acid derived carbon dots (CACDs) synthesized by hydrothermal treatment of citric acid and diethylenetriamine below 200 °C. After being purified using a gel permeation chromatography cleanup system, the complexity and chemical composition of the CACDs were evaluated by liquid chromatography coupled with high-resolution Fourier transform ion cyclotron resonance mass spectrometry. The fluorophores consisted of five-membered ring fused 2-pyridones identified as the photoluminescence origin. M06-2X density functional calculations, surface tension and morphological studies suggested DETA@5CA serves as the main building block to fabricate supramolecular aggregates. Then we proposed that the dimeric and trimeric fluorophores coupled with DETA@5CA led to “dot” topologies in the CACDs solution under the effect of hydrogen bonding. In aqueous solution, the CACDs exhibited narrowly dispersed optical properties and a high fluorescent quantum yield (∼98%). Moreover, the supramolecular interaction induced CACDs have high sensitivity under various ambient conditions, such as pH, organic solvents and metal ions.

How do organic gold compounds and organic halogen molecules interact? Comparison with hydrogen bonds

An Au⋯X interaction has been predicted in the complexes between the organic gold compound RAu (R = CH3, C2H3, and C2H) and the organic halogen compound R′X (R′ = CH3, C2H, C2H3, and CF3; X = Cl, Br, and I) using quantum chemical calculations. Upon the basis of the anisotropic distribution of molecular electrostatic potentials on the Au and X atoms, two types of structures, represented as GB and XB, respectively, were obtained. In the GB structure, the Au atom acts as a Lewis acid and X is a Lewis base, but reversed roles are found for Au and X in XB. Interestingly, the former structure is far more stable than the latter one. Their difference in stability can be regulated by the substitution and hybridization effects, similarly to those in hydrogen bonds. The partially covalent-interaction nature of GBs was characterized with the large charge transfer and the negative energy density as well as the high interaction energy. GB interaction is dominated by electrostatic and polarization energies, whereas electrostatic and dispersion energies are responsible for the stability of most XB complexes. This is an interesting finding that both patterns of interactions are different in nature even though the two monomers are only different in the spatial orientation for both interactions.

Origin of selenium–gold interaction in F2CSe⋯AuY (Y = CN, F, Cl, Br, OH, and CH3): Synergistic effects

Selenium-gold interaction plays an important role in crystal materials, molecular self-assembly, and pharmacochemistry involving gold. In this paper, we unveiled the mechanism and nature of selenium-gold interaction by studying complexes F2CSe⋯AuY (Y = CN, F, Cl, Br, OH, and CH3). The results showed that the formation of selenium-gold interaction is mainly attributed to the charge transfer from the lone pair of Se atom to the Au-Y anti-bonding orbital. Energy decomposition analysis indicated that the polarization energy is nearly equivalent to or exceeds the electrostatic term in the selenium-gold interaction. Interestingly, the chalcogen-gold interaction becomes stronger with the increase of chalcogen atomic mass in F2CX⋯AuCN (X = O, S, Se, and Te). The cyclic ternary complexes are formed with the introduction of NH3 into F2CSe⋯AuY, in which selenium-gold interaction is weakened and selenium-nitrogen interaction is strengthened due to the synergistic effects.