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  • Küçük Resim
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    Aromatization of triafulvene and its exocyclic Si, Ge, and Sn derivations by complexation with halogen atoms
    (Taylor & Francis Inc, 2017) Tokatlı, Ahmet; Ucun, Fatih; Oturak, Halil; Tunç, Fatmagül
    The geometries of triafulvene (TF) and its exocyclic Si, Ge, and Sn analogues complexes with F, Cl, Br, and I halogen atoms (TF(X)Y, XC, Si, Ge, and Sn; YF, Cl, Br, and I) were studied. The complexes were optimized at DFT(B3LYP)/6-311+G(d,p) level of theory. To assess the aromaticity of the considered complexes the geometry-based (HOMA), magnetism-based (NICS), and recently introduced electronic-based (electric field gradient (EFG(0); Shannon aromaticity (SA)) aromaticity indices were employed. The increasing tendency of aromaticity in each complex species was noted as the series of TF(X)F > TF(X)Cl > TF(X)Br > TF((X)I. Then, the binding energies corrected by basis set super position error (BSSE) were calculated by single point energy calculations at M06-2X/6-311+G(d,p) level. Natural bond orbital (NBO) analysis confirmed that the charge transfer takes place from TF(X) to the halogen atoms. Some topological parameters, within the framework of the quantum theory of atoms in molecules (QTAIM), were also calculated to estimate the aromaticity of the complexes. It was seen that there are some important correlations between the topological parameters and aromaticity indices. In addition the most striking finding was that all the TF(X) molecules are connected with the halogen atoms through YC1C2 () noncovalent interaction. This interaction was also investigated through noncovalent interaction (NCI) analysis.
  • Küçük Resim
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    Effect of external electric field on C-X ··· π halogen bonds
    (Springer, 2019) Tokatlı, Ahmet; Tunç, Fatmagül; Ucun, Fatih
    In this study, ab initio calculations (RI-MP2(full)/aug-cc-pVDZ) are performed to investigate the effect of an external electric field (EEF) on the nature, properties, and structures of C–X ··· ? halogen bonds in CF3Br complexes with ? systems (benzene, ethene, and ethyne), for the first time. This EEF effect is analyzed by a myriad of methods, including molecular electrostatic potential (MEP), symmetry adapted perturbation theory (SAPT), natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), and noncovalent interaction (NCI) methods. A linear relationship is found between RI-MP2 interaction energy and the strength of the EEF, indicating that the stability of C–X ··· ? halogen bonds is sensitive to both the strength and direction of the EEF. According to the SAPT analyses, when the EEF is applied along the +z direction (perpendicular to the ? plane), the nature of C–X ··· ? halogen bonds transforms gradually from dispersion to electrostatic for the CF3Br ··· benzene complex and from electrostatic to more electrostatic for the other complexes. However, when the EEF is applied along the –z direction, the C–X ··· ? halogen bonds in all the complexes tend to be more dispersive in nature. The QTAIM analysis exhibits that the CF3Br ··· benzene complex under the EEF with strength < 0.005 au is formed by the C–X ··· ?C3 and C–X ··· ?ring halogen bonds, while it has only the C–X ··· ?C3 halogen bond when the strength of the EEF is > 0.005 au. The structural results of the studied complexes show an inverse dependence of intermolecular distance between the CF3Br and ? system on the strength of the EEF.