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Competition between π...π interaction and halogen bond in solution has been investigated by using carbon nuclear magnetic resonance spectroscopy (13C NMR) combined with density functional theory calculation. Both experimental and theoretical results clearly show that there are no C-Cl...π or C-Br...π halogen bonds and only the π...π interactions exist in the binary liquid mixtures of C6D6 with C6F5Cl and C6F5Br, respectively. The case is totally different for the binary liquid mixtures of C6D6 with C6F5I in which the C-I...π halogen bonds not the π...π interactions are present. The important role of entropy in the competition between π...π interaction and halogen bond in solution was also discussed. [ABSTRACT FROM AUTHOR]

The C-Hal (Hal = Cl, Br, or I) bond-length change and the corresponding vibrational frequency shift of the C-Hal stretch upon the C-Hal ...Y (Y is the electron donor) halogen bond formation have been determined by using density functional theory computations. Plots of the C-Hal bond-length change versus the corresponding vibrational frequency shift of the C-Hal stretch all give straight lines. The coefficients of determination range from 0.94366 to 0.99219, showing that the correlation between the C-Hal bond-length change and the corresponding frequency shift is very good in the halogen-bonded complexes. The possible effects of vibrational coupling, computational method, and anharmonicity on the bond-length change-frequency shift correlation are discussed in detail. [ABSTRACT FROM AUTHOR]

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X-H or X-Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X-H or X-Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X-H bond involved in the formation of the hydrogen bond and the X-Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated. [ABSTRACT FROM AUTHOR]

The M05-class (M05 and M05-2X) and M06-class (M06, M06-2X, M06-HF, and M06-L) functionals, developed by Zhao and Truhlar, have shown better performance than popular older DFT functionals in obtaining accurate binding energies of noncovalent complexes. However, the reliability of these functionals for the structure and geometry of noncovalent systems was seldom assessed. Here, using the MP2/aug-cc-pVTZ values as a benchmark, we assessed the performance of the M05-class and M06-class functionals for the structure and geometry of the hydrogen-bonded and halogen-bonded complexes. The results clearly show that the M05, M06 and M06L functionals totally fail to predict the structure of the hydrogen-bonded complex formed between glycine and carbonic acid whereas the M05-2X, M06-2X, M06-HF, and even B3LYP succeed. For the geometries of a series of halogen-bonded complexes, it is found that the M05-2X functional performs slightly better than the M06-2X and M06-HF functionals and much better than the M05, M06 and M06-L functionals on average. Based on these tests, we concluded that the M05, M06 and M06-L functionals are not good for the study of the structure and geometry of the hydrogen-bonded and halogen-bonded complexes and the density functional M05-2X is the best choice. In addition, we have also assessed the integration grid errors arising from the numerical integration of these functionals for the structure and geometry of the hydrogen-bonded and halogen-bonded complexes. [ABSTRACT FROM AUTHOR]

B3LYP and MP2 methods were employed to optimize thirteen conformers of (N–Cl)-glycine using 6-311++G** basis set. Single-point MPn (n=2–4) calculations using the same basis set were carried out in order to confirm the reliabilities of B3LYP and MP2 on energies and relative stabilities for the glycine derivative. On the other hand, the effects of zero-point vibrational energy and electron correlation on the relative stabilities of different (N–Cl)-glycine conformers were discussed by comparing results from these theoretical calculations. It was found from the calculations above that B3LYP method could provide geometry structure very similar to MP2 theory for (N–Cl)-glycine. But the relative stabilities of the conformers of (N–Cl)-glycine predicted by MP2 method are in more agreement with high-level MP4(SDTQ) than B3LYP. The zero-point vibrational energy plays an important role on relative stabilities of some conformers for MP2 methods, but not for B3LYP. Significant effects of electron correlation on the relative energies of (N–Cl)-glycine conformation were observed by means of different treatments for electron correlation. Natural Bond Orbital and Atoms in Molecule analyses were performed to determine the existence of intramolecular hydrogen bond, which indicate that only three conformers have intramolecular hydrogen bonds. Furthermore, NBO is also employed to investigate quantitatively hyperconjugation in the conformers in order to account for conformational preference. Our results point out that hyperconjugations are responsible for the relative stability of most conformers. While for conformers containing hydrogen bond, the origin of relative stability comes from the balance of H-bond and hyperconjugative effect. [Copyright &y& Elsevier]

The structures, interaction energies, electronic properties for different conformers of glycine(Ip)–water complex have been determined employing density functional theory using the B3LYP hybrid exchange-correlation functional with the Pople''s standard basis sets. Ab initio MP2 calculations were carried out to verify the appropriateness of the B3LYP methods for glycine(Ip)–water system. The basis set superposition error has been eliminated by using the full counterpoise correction method. The results from CP-corrected gradient optimization and the ones from CP-uncorrected were also compared. At last, the vibrational frequencies of the most stable conformer A(C1) were discussed. [Copyright &y& Elsevier]

Abstract: A new class of halogen bonds of the type X=Hal⋯Y has been investigated by using the density functional theory calculations. The strength of this new class of halogen bonds is in the range of 90–120kcal/mol, which is greatly larger than that of the conventional halogen bond of the type X-Hal⋯Y. The geometry of this new class of halogen bonds is not determined by the halogen’s positive σ-hole. Natural bond orbital analysis shows it is the n → π ∗ interaction that determines the geometry of this new class of halogen bonds. Experimental results are in good agreement with the theoretical predictions. [Copyright &y& Elsevier]

Abstract: Density functional theory calculations were carried out for hydrogen atom binding on small Ag n Cu m clusters (n + m ⩽5). It was found that hydrogen prefers to bind with Cu atoms when both Ag and Cu site co-exist in the cluster. In general the binding energies increase with the increasing Cu content for the given cluster size. The metal–H frequencies vary according to the way the metal atoms bound with hydrogen. The most favorable dissociation channels and the corresponding dissociation energies for the most stable bare clusters and cluster hydrides are determined. [ABSTRACT FROM AUTHOR]