Dispersion Energy Components Research Articles

Preparation and characterization of N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals by physical vapour transport (PVT) technique

Good quality of N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals (space group Pna21, point group mm2) having different morphologies were successfully grown from vapour phase for the first time by physical vapour transport technique under predefined supersaturation conditions. BNA single crystals of different morphologies resulted at different supersaturation conditions: prismatic (σ = 0.0218 to 0.1553), columnar (σ = 0.1553 to 0.4652), needle (σ = 0.4652 to 0.7245), fine-needle (σ = 0.7245 to 0.9166) and dendritic (σ = 0.9166 to 0.9729). The predicted theoretical morphologies using BFDH, and attachment energy models are in line with the experimental morphologies. The slice thickness, slice energy, attachment energy and anisotropic growth factor of different faces were determined which reveals that {020} are the slow-growing and morphologically important facets amongst others present in the grown BNA single crystal. Fast growth along ‘+c’ direction and no growth along ‘-c’ direction was identified due to the supersaturation-dependant anisotropic growth nature of BNA. Crystal purity and quality are confirmed by single crystal X-ray diffraction study. In addition, the role of intermolecular interactions, electrostatic, polarization, repulsion and dispersion energy components involved in the crystal packing to stabilize the BNA single crystal were characterized by the Crystal Explorer 17.5 software. Computed energy frameworks confirm that the dispersion energy component is predominantly contributing to the crystal packing than the Coulombic interaction energies.

Synthesis, structural and computational studies of a novel anionic synthon and its derivatives

A novel trimethylsilyl anionic synthon: 9-(4'-trimethylsilyl-1',2',3'-triazol-1'-yl)methylanthracene was synthesized by copper catalyzed reaction of 9- chloromethylanthracene, trimethylsilyl acetylene and sodium azide using dimethylformamide as solvent, in 95% yield. Good quality crystals obtained were subjected to X-ray diffraction studies and for the first instance of time, single crystal X-ray diffraction analysis of 9-(4'-trimethylsilyl-1',2',3'-triazol-1'-yl)methylanthracene is reported. The X-ray diffraction studies reveal that the compound crystallizes in monoclinic crystal system, with space group of P21/c. The molecular structure analysis show the anthracene- and triazolyl- ring systems being inclined to each other with a dihedral angle of 68.53(2)o. The crystal structure was governed by intermolecular C–H…N interactions. The intermolecular interactions were investigated by Hirshfeld surfaces and its related fingerprint plots indicate H...H interactions to be the predominant one towards the packing of three dimensional Hirshfeld surfaces. Also, the three dimensional interaction energies in a crystal were computed using energy model of B3LYP/6-31G(d,p) and their results showed that the dispersion energy components were dominated by electrostatic components. The density functional theory studies were carried out for the compound C20H21N3Si to investigate electronic properties, and chemical reactivity. Further, the novel compound was protodesilylated by potassium fluoride in methanol solvent to obtain 9-(1',2',3'-triazol-1'-yl)methylanthracene, in 94% yield. Novel 9-(1',2',3'-triazol-1'-yl)methylanthracene was subjected to molecular docking and corrosion inhibitory studies.

Spectral studies and crystal structures of molybdenum(VI) complexes containing pyridine or picoline as auxiliary ligands: interaction energy calculations and free radical scavenging studies

Three cis-MoO2 complexes [MoO2(CAB)(py)] (1), [MoO2(CAB)(3-pic)] (2) and [MoO2(CAB)(4-pic)] (3) which vary in the nature of the heterocyclic bases in the auxiliary coordination site derived from an ONO donor aroylhydrazone (H2CAB) have been synthesized and characterized by various physicochemical methods. The single-crystal X-ray diffraction studies reveal that the complexes adopt a distorted octahedral N2O4 coordination sphere around the Mo(VI) center in which the ONO donor atoms of hydrazone moiety and one oxido oxygen constitute the NO3 basal plane and the axial position by the other oxido oxygen and nitrogen atom of coordinated pyridine molecule in [MoO2(CAB)(py)] (1) or picoline molecule in [MoO2(CAB)(3-pic)] (2) and [MoO2(CAB)(4-pic)] (3). The hydrogen bonding interaction generates a two-dimensional supramolecular sheet-like architecture in [MoO2(CAB)(py)] (1) and [MoO2(CAB)(3-pic)] (2), whereas a three-dimensional network was observed in [MoO2(CAB)(4-pic)] (3). The interaction energy calculations reveal that the dispersion energy component dominates over other components and [MoO2(CAB)(3-pic)] (2) is found to be energetically more stable. Furthermore, the aroylhydrazone shows free radical scavenging activity, whereas the complexes are inactive.

Revealing the Surface Effect on Gas Transport and Mechanical Properties in Nonporous Polymeric Membranes in Terms of Surface Free Energy.

The contribution of surface roughness of nonporous polymeric membranes to their gas separation and mechanical properties was studied in terms of surface free energy. The membranes samples were prepared based on glassy polymers with different chain rigidity, namely polysulfone (PSU), cellulose triacetate (CTA), and poly(vinyl alcohol) (PVA). The results were obtained by atomic force and scanning electron microscopy (AFM and SEM) with individual gas permeation, wettability, and mechanical testing. The specific surface free energy (as well as its polar and dispersive components) for the polymers was calculated by the Owens-Wendt method. It was proven that the surface roughness of the polymer membranes affects both energy components; however, the degree of this influence depends on the chemical nature of the corresponding polymer. Moreover, it was assumed that the dispersive energy component is inversely correlated with any gases' total permeability. In contrast, the polar one is inversely correlated with the permeability by gases with the ability for site-specific interactions. The gas separation results confirmed this assumption. It was also shown that the mechanical properties of the polymer membranes are also influenced by the surface energy, namely, its dispersive component.

Supramolecular frameworks formed via hydrogen bonding and non-covalent interactions and interaction energy calculations of solvent coordinated cis-dioxomolybdenum(VI) complexes derived from ONO donor aroylhydrazone: Cytotoxicity studies

A tridentate ONO donor aroylhydrazone, 3,5-diiodosalicylaldehyde-4-methoxybenzoylhydrazone (H2SMB) and four cis-MoO2 complexes [MoO2(SMB)(DMF)] (1), [MoO2(SMB)(DMSO)] (2), [MoO2(SMB)(py)] (3) and [MoO2(SMB)(3-pic)] (4) which vary the solvents/heterocyclic bases in the sixth coordination position have been synthesised. The compounds were characterized by different physico-chemical methods. The single crystal X-ray diffraction studies unambiguously confirm the molecular structures. In the complexes 1, 2, 3 and 4, the octahedral geometry around the Mo(VI) central atom is satisfied by ONO donor atoms and two oxo oxygens, the sixth coordination site is occupied by oxygen/nitrogen atoms of solvent molecules. The supramolecular architectures generated by various hydrogen bonding and non-bonding interactions were investigated. The interaction energy calculations reveal dominance of dispersion energy component over other components. The aroylhydrazone was screened for antioxidant study using DPPH assay. The in vitro cytotoxicity of Mo(VI) complexes was evaluated against lymphoma ascites cell line as well as against normal cell and compared to hydrazone and cyclophosphamide.

Quantitative investigation on the intermolecular interactions present in 8-(4-ethoxyphenyl)-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione with insight from interaction energies, energy framework, electrostatic potential map and fingerprint analysis

In this study, we have performed a detailed quantitative analysis of the different intermolecular interactions present in 8-(4-ethoxyphenyl)-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione (I). The molecule crystallizes in the P-1 space group with one molecule in the asymmetric unit. The molecule had a layered crystal packing wherein the molecular sheets are primarily formed by hydrogen bonds and the stabilization is dominated via the electrostatic energy contribution. This molecular sheet is then interconnected to other similar sheets via different stacking motifs with significant contribution from dispersion energy components. The quantitative investigation of intermolecular interactions in a xanthine derivative reveals that there is an anisotropic distribution of interaction energies (coulombic and dispersion) along different directions, indicating possible applications of this class of molecules in the design of new materials.

Mononuclear and binuclear dioxidomolybdenum(VI) complexes of ONO appended aroylhydrazone: Crystal structures, interaction energy calculation and cytotoxicity

Mono- and binuclear cis-MoO2 complexes (1–3) having the general formula [MoO2(ISF)D] (D = H2O (complex 1), DMSO (complex 2) and 4,4ꞌ-bipyridine (complex 3) ISF = 3,5-diiodosalicyaldehyde-2-furoichydrazone) have been synthesized and fully characterized by different physico-chemical methods. The molecular structures were confirmed unambiguously by single crystal X-ray diffraction studies. The octahedral geometry around the Mo(VI) central atom is satisfied by O, N, O donor atoms of dideprotonated dianionic hydrazone moiety, two oxido oxygens and oxygen/nitrogen atoms of the coordinated solvent molecules. The asymmetric unit of complexes 1 and 2 contains one molecule whereas complex 3 contains only half of the molecule. The 4,4ꞌ-bipyridine molecule acts as a linker that links the two asymmetric MoO2D moieties to form the binuclear dioxidomolybdenum(VI) in complex 3 with Mo⋯Mo non-bonding distance of 12.01(10) Å. The relevance of hydrogen bonding and non-bonding interactions in the construction of supramolecular architectures were investigated. The upshots of single crystal studies were reproduced with the aid Hirshfeld surface studies. The pre-eminence of dispersion energy component over other components was established by interaction energy calculations and the energy framework analysis. The average interaction energy values for complexes 2 and 3 are found to be −282.3 and −228.3 kJ mol−1 respectively. Furthermore the in vitro cytotoxicity of all the synthesized compounds was evaluated against lymphoma ascites cell line.

Molecular structure, DFT studies, Hirshfeld surface analysis, energy frameworks, and molecular docking studies of novel (E)-1-(4-chlorophenyl)-5-methyl-N′-((3-methyl-5-phenoxy-1-phenyl-1H-pyrazol-4-yl) methylene)-1H-1, 2, 3-triazole-4-carbohydrazide

The synthesis of the compound and its crystal structure having a monoclinic crystal system has been reported earlier. Optimized bond lengths and angles are showing good agreements with experimental data using DFT/B3LYP method. Energy of highest occupied molecular orbital and lowest unoccupied molecular orbital has been predicted to analyze the stabilities of compound. Crystal explorer 17.5 helps to visualize intermolecular interactions and its contributions to each interaction within molecule. The preeminence of dispersion energy component over the other components was established by interaction energy calculations and lattice energy framework analysis using same software. The molecular docking study was performed for molecule using AutoDock software.

DFT analysis of the linkage isomerism in penta(ammine)ruthenium(II/III) complexes of benzotriazole: Natural bond orbital method approach and a comprehensive energy decomposition analysis.

Penta(ammine)ruthenium benzotriazole complexes [RuII/III (NH3 )5 bta]+/2+ and [RuII/III (NH3 )5 btaH]2+/3+ (bta and btaH are the deprotonated and neutral form of the triazole ligand, respectively) can exhibit two linkage isomers κN1 and κN2. This system was investigated by density functional theory natural bond orbitals analysis and Su-Li energy decomposition analysis. Steric, electrostatic, exchange, repulsion, polarization, and dispersion energy components of the total metal-ligand interaction were quantitatively evaluated, and revealed that the overall metal-triazole ligand is comprised of donor-acceptor interactions like σ-donation and π-back-donation, which favors a specific isomer depending on the oxidation state of the ruthenium and the charge of the ligand. Further, activation energies (ΔG‡ ) for linkage isomerization reactions were calculated. Results were correlated with experimental chemical-electrochemical data and two plausible mechanisms are discussed. © 2019 Wiley Periodicals, Inc.

Structure-Packing-Property Correlation of Self-Sorted Versus Interdigitated Assembly in TTF⋅TCNQ-Based Charge-Transport Materials.

Among the various donor-acceptor (D-A) charge-transfer co-crystals investigated in the past few decades, tetrathiafulvalene-tetracyanoquinodimethane (F⋅Q, popularly known as TTF⋅TCNQ)-based co-crystals have fascinated materials chemists owing to their exceptional conducting and magnetic properties that arise from the packing in crystal structures. Here, crystallographic information files of eighteen F⋅Q-based co-crystals are extracted from the Cambridge Structural Database (CSD) and classified into Class 1 (D-on-D and A-on-A segregated stacks; F⋅Q, F1⋅Q-F6⋅Q, and F⋅Q1), Class 2 (-A-D-A-D-A-D- mixed stacks; F6a⋅Q-F11⋅Q and F⋅Q2), and Class 3 [-A-D-A-A-D-A-; Class 3a (F12⋅Q and F13⋅Q) and -D-D-A-A-; Class 3b (F14⋅Q)] systems according to their packing modes. Hirshfeld surface analysis, PIXEL energy calculations, and quantum theory of atoms in molecules (QTAIM) analysis are performed on the selected multicomponent charge-transfer crystals for the first time, in an attempt to explore the driving forces that give rise to different classes of 3 D crystal packing, which in turn mandates the expedient electronic properties exhibited by the investigated co-crystals. PIXEL calculations reveal that the dispersion energy component makes the maximum contribution to the total lattice energy for most of the F⋅Q-based co-crystals under study. Although the Q-on-Q dimer is the energetically most favored dimer in F⋅Q, the substituents on F capable of forming hydrogen-bonding, C⋅⋅⋅S, and other weak intermolecular interactions result in the greater stability of the F-on-F dimer for F1⋅Q-F6⋅Q (except F2⋅Q). The C⋅⋅⋅S, Csp ⋅⋅⋅S, S⋅⋅⋅N, and π⋅⋅⋅π interaction-driven D-on-A dimer is found to be the most stable dimer of all the Class 2 co-crystals. Band structure and density-of-state calculations of the representative co-crystals in each class indicate different electronic structures according to the packing arrangement. F⋅Q and F6⋅Q with a high interaction of electronic orbitals between D-on-D and A-on-A in segregated stacks are found to be metal-like (bandgap, Eg =0.003 eV) and metallic (overlapping bands in the Fermi level), respectively, whereas the polymorph of F6⋅Q belonging to Class 2 (F6a⋅Q) displays a semiconductor-type band structure (Eg =0.053 eV). F12⋅Q of Class 3a exhibits a metal-like band structure (Eg =0.001 eV). The fine tuning of chromophores with diverse functional substituents capable of triggering weak intermolecular interactions that give rise to the desired packing and charge-transfer properties has the potential to open floodgates of opportunity for research in the chemistry of materials and fabrication of efficient electronic devices.

Comparison of wet milling and dry milling routes for ibuprofen pharmaceutical crystals and their impact on pharmaceutical and biopharmaceutical properties

Understanding the differences between wet milling (WM) and the dry milling (DM) is crucial in selecting the methodology used in pharmaceutical milling processes. This research examined WM and DM processes for ibuprofen (IBU), a Biopharmaceutics Classification System (BCS) class II drug (low solubility, high permeability). A design of experiment (DOE) was performed for each route of milling using the Comil, with rotor speed, sieve size, milling time and rotor shape selected as variables. Solid state characterization was performed on pre- and post-milled samples by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). Screen size and speed were observed to be the most important factors in terms of milled particle size, where lower screen size and high speed resulted in smaller particle size. WM resulted in smaller size and larger specific surface area (SSA) compared to DM, when the same milling parameters were used for both processes. It was observed that rotor shape had a negligible impact on particle size. It was observed that the wet-milled samples demonstrated better flow and faster dissolution for the same run (same milling parameters) in the DOE (statistically significant p < 0.05). Differences in measured surface energy values were consistent with differences in the dissolution rates observed. The development of electrostatic charge and/or differences in surface energy as a result of DM probably resulted in particle agglomeration, which resulted in a larger particle size, poor flow performance, and poor dissolution performance. This hypothesis is supported by differences in the dispersive energy component calculated from contact angle measurements (statistically significant p < 0.05). These results indicate that, for IBU, WM would be a better option than DM to facilitate particle size reduction with subsequent improvement in the powder dissolution behaviour and flow properties. The findings presented in this study may be applicable to BCS class II molecules which have poor flow properties due to electrostatic charging on dry milling.

Influence of the Substituents on the CH...π Interaction: Benzene–Methane Complex

Recently we showed that the binding energy of the benzene...acetylene complex could be tuned up to 5 kcal/mol by substituting the hydrogen atoms of the benzene molecule with multiple electron-donating/electron-withdrawing groups (J. Chem. Theory Comput. 2012, 8, 1935). In continuation, we have here examined the influence of various substituents on the CH...π interaction present in the benzene...methane complex using the CCSD(T) method at the complete basis set limit. The influence of multiple fluoro substituents on the interaction strength of the benzene...methane complex was found to be insignificant, while the interaction strength linearly increases with successive addition of methyl groups. The influence of other substituents such as CN, NO2, COOH, Cl, and OH was found to be negligible. The NH2 group enhances the binding strength similarly to the methyl group. Energy decomposition analysis predicts the dispersion energy component to be on an average three times larger than the electrostatic energy component. Multidimensional correlation analysis shows that the exchange-repulsion and dispersion terms are correlated very well with the interaction distance (r) and with a combination of the interaction distance (r) and molar refractivity (MR), while the electrostatic component correlates well when the Hammett constant is used in combination with the interaction distance (r). Various recently developed DFT methods were used to assess their ability to predict the binding energy of various substituted benzene...methane complexes, and the M06-2X, B97-D, and B3LYP-D3 methods were found to be the best performers, giving a mean absolute deviation of ∼0.15 kcal/mol.

Sulfur, Not Too Far Behind O, N, and C: SH···π Hydrogen Bond

We report hydrogen-bonded complexes of H(2)S with indole and 3-methyl indole stabilized by the S-H...pi interaction. It is interesting to discover that although sulfur and its hydrides are known as poor hydrogen-bond donor/acceptors, sulfur is not too far behind oxygen, nitrogen, and carbon in regard to forming the pi-type hydrogen bonds. This report also extends the scope of our earlier studies from sigma-type hydrogen-bonded complexes of sulfur (O-H...S and N-H...S sigma-type hydrogen-bonded complexes) to pi-type hydrogen-bonded complexes of sulfur (S-H...pi pi-type hydrogen-bonded complexes). The experiments were carried out using the supersonic jet expansion technique, and the complexes were probed using laser-induced spectroscopy such as laser-induced fluorescence (LIF), resonant two-photon inonization (R2PI), and fluorescence dip infrared spectroscopy (FDIRS). The FDIR spectroscopy revealed that while there was no shift in the N-H stretch, the S-H stretch was red shifted by about 21 cm(-1). For the H(2)O complexes of indole and 3-methylindole, however, there was a significant red shift in the N-H stretch. These observations suggest that H(2)O forms a NH...O type complex, whereas H(2)S prefers to form a SH...pi type complex. The experimental results were complemented by ab initio calculations and energy decomposition analysis. The binding energies for both the sigma-type and pi-type hydrogen-bonded M.L complexes (M = indole and 3-methylindole; L = H(2)O and H(2)S) were calculated by extrapolating MP2 interaction energies to the complete basis set limit. The calculated M.H(2)S (sigma-type) interaction energy (2.74 kcal/mol) was considerably smaller than that of the M.H(2)S pi-type hydrogen-bonded complex (4.89 kcal/mol), which is exactly opposite of the trend found for the M.H(2)O complexes. This is consistent with the experimental observations. Comparison of the S-H...pi interaction with the other type of X-H...pi (X = C, N, and O) shows that the S-H...pi interaction is the strongest among them. In all of the pi-type HB complexes, the dispersion energy component has significant contribution to the total binding energy.

B3LYP and MP2 Calculations of the Enthalpies of Hydrogen-Bonded Complexes of Methanol with Neutral Bases and Anions: Comparison with Experimental Data

To perfect a method for building a theoretical hydrogen-bond basicity scale, the enthalpy of hydrogen bonding between methanol and thirteen neutral and anionic bases (MeOH, MeNH2, Me2NH, Et2NH, Me3N, Et3N, Br-, CN-, SH-, Cl-, HCOO-, MeO-, F-) was calculated by DFT and ab initio methods. The theoretical results were compared to selected experimental ones. It appears that B3LYP/6-31+G(d,p) calculations are satisfactory for optimizing the geometry of complexes and giving a general order of basicity. However, they are deficient for reproducing the large effect of alkyl groups on the hydrogen-bond basicity of amines. This deficiency is explained by intermolecular perturbation theory calculations, which show that the alkylation of nitrogen dramatically increases the dispersion energy component not taken into account by the B3LYP functional. Of the methods considered, only MP2/aug-cc-pVTZ calculations are capable of reproducing the binding enthalpy within the experimental error for the first-row acceptor atoms N, O, and F, and of accounting for dispersion effects created by alkylation at the hydrogen-bond acceptor site.

Silicone oil adhesion to intraocular lenses: An experimental study comparing various biomaterials

Purpose: To perform an in vitro experimental study comparing the degree of adherence of silicone oil to various rigid and foldable intraocular lens (IOL) designs and to the human lens capsule.Setting: Center for Research on Ocular Therapeutics and Biodevices, Department of Ophthalmology, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.Methods: Seven IOL styles comprising various biomaterials were studied: fluorinetreated (FIuoriens™), heparin-surface-modified (HSM™), hydrogel, Memory-Lens™, poly(methyl methacrylate) (PMMA), soft acrylic, and silicone lenses; the human crystalline lens was also studied. Each lens was immersed in silicone oil for 12 hours, then photographed, studied by scanning electron microscopy (except the crystalline lens), and subjected to computer-generated image analysis to determine the silicone oil coverage.Results: Silicone oil coverage of dry silicone lenses was 100% and of lenses immersed in normal saline, 82.5%. The least coverage was on the heparin-surfacemodified lens (mean score 9.4%). Coverage of the other four lenses ranged from approximately 15.1% to 33.7%. Mean coverage of the human lens capsule was 10.9%.Conclusion: Although a silicone IOL shows maximal adherence to silicone oil, other lens biomaterials are not immune to this complication. Silicone oil coverage was related to the dispersive energy component of the surface charge of the IOL biomaterial. Low dispersive energy materials had less silicone oil coverage, while those with higher dispersive energy had more oil coverage.

Basis set effects on the intermolecular interaction of hydrocarbon molecules obtained by an ab initio molecular orbital method: evaluation of dispersion energy

The intermolecular interaction potentials of methane, ethane, ethylene and benzene dimers were calculated using several basis sets [up to 6–311G(3d,4p)] with electron correlation correction by the Møller-Plesset perturbation method and basis set superposition error (BSSE) correction. The calculated interaction energies considerably depend on the basis set used. Whereas the interaction energies of the repulsive and Coulombic energy components calculated at the HF level are not affected by the change of the basis set, the dispersion energy component, calculated as the electron correlation energy, greatly depends on the basis set used. A basis set with multiple polarized functions is necessary to calculate the dispersion energy correctly. The use of small basis sets greatly underestimates the dispersion energy.

Basis set effects on the intermolecular interaction of the H 2-H 2 system obtained using ab initio molecular orbital calculations with the Møller-Plesset perturbation correction

The intermolecular interaction potential of the H 2-H 2 system was calculated by an ab initio molecular orbital method using several basis sets (up to 6-31 lG(3pd)) with inclusion of the electron correlation correction of the Møller-Plesset perturbation method and the basis set superposition error (BSSE) correction of the counterpoise method in order to evaluate the basis set effect. The calculated interaction energies depend strongly on the basis set used. Whereas the interaction energies of the repulsive and coulombic energy components calculated at the Hartree-Fock level are not affected by a change of basis set, the dispersion energy component depends strongly on the basis set used. Parameters of an exp-6-1 type non-bonding interaction potential were optimized on the basis of the MP4(SDTQ)/6-311G(3p) level intermolecular interaction energies of the H 2-H 2 system.

Basis set effects on the intermolecular interaction energies of methane dimers obtained by the Moeller-Plesset perturbation theory calculation

Intermolecular interaction energies of methane dimer were calculated by using several basis sets up to 6-311G(3d,4p) with electron correlation energy correction by the Moeller-Plesset perturbation method and basis set superposition error (BSSE) correction by the counterpoise method to evaluate the basis set effect. The calculated interaction energies depended on the basis set considerably. Whereas the interaction energies of repulsive component calculated at HF level were not affected by the change of basis set, the dispersion energy component dependent greatly on the basis set used. The dispersion energies calculated with the Moeller-Plesset second- and third-order perturbation by using 6-311G(2d,2p) basis set were 0-10% and 4-6% smaller than those obtained with the fourth-order (MP4(SDTQ)) perturbation, respectively. The BSSE's calculated by the counterpoise method were still about 30% of the calculated intermolecular interaction energies for the conformers of energy minima event at the MP4(SDTQ)/6-311G(2d,2p) level. The calculated interaction potentials of dimers at the MP4(SDTQ)/6-311G(2d,2p) level were considerably shallower than those obtained by MM2 force fields but were close to the potentials given by the Williams potential and by the recently reported MM3 force field.