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Described are two experimental findings: (1) selective CO2 uptake by dipeptide-based molecular crystals of Boc- L -methionyl- L -alanine methyl ester 1 with seemingly nonporous crystal architecture and (2) its CO2 sorption state successfully visualized at the atomic level by means of in situ X-ray crystallographic analysis. More important was the latter, from which intermolecular interactions between CO2 and the surrounding molecules of 1 in the crystal were analyzed by ab initio calculations, indicating that attraction between them was mainly composed of a dispersion force. In addition, a comparison study of the crystal structure of 1 with those of analogous dipeptide crystals (isomorphous with 1) demonstrated that the thermal fluctuations of the dipeptide molecules in the solid state triggered CO2 permeation into the isolated voids present in the crystal lattice of 1. [ABSTRACT FROM AUTHOR]

The CCSD(T) level interaction energies of eight orientations of nitrobenzene-benzene complexes and nine orientations of nitrobenzene dimers at the basis set limit have been estimated. The calculated interaction energy of the most stable slipped-parallel (Cs) nitrobenzene-benzene complex was -4.51 kcal/mol. That of the most stable slipped-parallel (antiparallel) (C2h) nitrobenzene dimer was -6.81 kcal/mol. The interaction energies of these complexes are significantly larger than that of the benzene dimer. The T-shaped complexes are substantially less stable. Although nitrobenzene has a polar nitro group, electrostatic interaction is always considerably weaker than the dispersion interaction. The dispersion interaction in these complexes is larger than that in the benzene dimer, which is the cause of the preference of the slipped-parallel orientation in these complexes. [ABSTRACT FROM AUTHOR]

The intermolecular interaction energies of naphthalene dimers have been calculated by using an aromatic intermolecular interaction model (a model chemistry for the evaluation of intermolecular interactions between aromatic molecules). The CCSD(T) (coupled cluster calculations with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the second-order Møller–Plesset perturbation interaction energy near saturation and the CCSD(T) correction term obtained using a medium-size basis set. The estimated interaction energies of the set of geometries explored in this work show that two structures emerge as being the lowest energy, and may effectively be considered as isoenergetic on the basis of the errors inherent in out extrapolation procedure. These structures are the slipped-parallel (C[sub i]) structure (-5.73 kcal/mol) and the cross (D[sub 2d]) structure (-5.28 kcal/mol). The T-shaped (C[sub 2v]) and sandwich (D[sub 2h]) dimers are substantially less stable (-4.34 and -3.78 kcal/mol, respectively). The dispersion interaction is found to be the major source of attraction in the naphthalene dimer. The electrostatic interaction is substantially smaller than the dispersion interaction. The large dispersion interaction is the cause of the large binding energies of the cross and slipped-parallel dimers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the intermolecular interaction potential of the carbon dioxide dimer. Absence of an inversion barrier; Calculation of the energy difference of the dimer; Use of diffuse polarization in evaluating the essential attractive interactions.

The intermolecular interaction energies of thiophene dimers have been calculated by using an aromatic intermolecular interaction (AIMI) model (a model chemistry for the evaluation of intermolecular interactions between aromatic molecules). The CCSD(T) interaction energy at the basis set limit has been estimated from the MP2 interaction energy near the basis set limit and the CCSD(T) correction term obtained by using a medium-size basis set. The calculated interaction energies of the parallel and perpendicular thiophene dimers are 1.71 and -3.12 kcal/mol, respectively. The substantial attractive interaction in the thiophene dimer, even where the molecules are well separated, shows that the major source of attraction is not short-range interactions such as charge transfer but rather long-range interactions such as electrostatic and dispersion. The inclusion of electron correlation increases the attraction significantly. The dispersion interaction is found to be the major source of attraction in the thiophene dimer. The calculated total interaction energy of the thiophene dimer is highly orientation dependent. Although electrostatic interaction is substantially weaker than dispersion interaction, it is highly orientation dependent, and therefore electrostatic interaction play an important role in the orientation dependence of the total interaction energy. The large attractive interaction in the perpendicular dimer is the cause of the preference for the herringbone structure in the crystals of nonsubstituted oligothiophenes (α-terthienyls), and the steric repulsion between the β-substituents is the cause of the π-stacked structure in the crystals of some β-substituted oligothiophenes. [ABSTRACT FROM AUTHOR]

Focuses on the model chemistry developed for the evaluation of intermolecular interaction between aromatic molecules. Effects of electron correlation inclusion on the attraction level; Consideration of dispersion interaction as the major source of benzene dimer attraction; Difference between electrostatic and dispersion interaction.

The performance of density functional theory using the Perdew and Wang's exchange and correlation functionals (PW91) functional for the prediction of intermolecular interaction energies is evaluated based on calculations on the neon, argon, methane, ethylene, and benzene dimers, as well as on 12 hydrogen bonded complexes (water, methanol, formic acid, hydrogen fluoride, ammonia, formamide dimers and water-methanol, water-dimethyl ether, water-formaldehyde, hydrogen cyanide-hydrogen fluoride, water-ammonia, water-formamide complexes). The results were compared with those obtained from Becke's exchange and Lee, Yang, and Parr's correlation functionals (BLYP), Becke's 3 parameter functional combined with Lee, Yang, and Parr's correlation functional (B3LYP), second order Mo\ller-Plesset perturbation (MP2), and coupled cluster calculations with single and double substitutions and with non-iterative triple corrections [CCSD(T)] calculations. The calculated interaction energies show that the PW91 functional performs much better than the BLYP or B3LYP functionals. The error in the computed binding energies of the hydrogen bonded complexes is 20% in the worst case. The most demanding cases are the systems with large dispersion contributions to the binding energy, such as the benzene dimer. In contrast to the BLYP and B3LYP functionals which fail to account for dispersion, the PW91 functional at least partly recovers the attraction. The basis set dependence of the PW91 functionals is relatively small in contrast to the MP2 and CCSD(T) methods. Despite its occasional difficulties with dispersion interaction, the PW91 functional may be a viable alternative to the ab initio methods, certainly in situations where large complexes are being studied. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]