MP2, DFT‐D, and PCM study of the HMB–TCNE complex: Thermodynamics, electric properties, and solvent effects

Abstract

Geometry, thermodynamic, and electric properties of the -EDA complex between hexamethylbenzene (HMB) and tetracyanoethylene (TCNE) are investigated at the MP2/6-31G* and, partly, DFT-D/6-31G* levels. Solvent effects on the properties are evaluated using the PCM model. Fully optimized HMB-TCNE geometry in gas phase is a stacking complex with an interplanar distance 2.87 ϫ 10 Ϫ10 m and the corresponding BSSE corrected interaction energy is Ϫ51.3 kJ mol Ϫ1. As expected, the interplanar distance is much shorter in comparison with HF and DFT results. However the crystal structures of both (HMB) 2 -TCNE and HMB-TCNE complexes have interplanar distances somewhat larger (3.18 and 3.28 ϫ 10 Ϫ10 m, respectively) than our MP2 gas phase value. Our estimate of the distance in CCl 4 on the basis of PCM solvent effect study is also larger (3.06 -3.16 ϫ 10 Ϫ10 m). The calculated enthalpy, entropy, Gibbs energy, and equilibrium constant of HMB-TCNE complex formation in gas phase are:, and K ϭ 2,100 dm 3 mol Ϫ1 . Experimental data, however, measured in CCl 4 are significantly lower:, and K ϭ 190 dm 3 mol Ϫ1 . The differences are caused by solvation effects which stabilize more the isolated components than the complex. The total solvent destabilization of Gibbs energy of the complex relatively to that of components is equal to 5.9 kJ mol Ϫ1 which is very close to our PCM value 6.5 kJ mol Ϫ1 . MP2/6-31G* dipole moment and polarizabilities are in reasonable agreement with experiment (3.56 D versus 2.8 D for dipole moment). The difference here is due to solvent effect which enlarges interplanar distance and thus decreases dipole moment value. The MP2/6-31G* study supplemented by DFT-D parameterization for enthalpy calculation, and by the PCM approach to include solvent effect seems to be proper tools to elucidate the properties of -EDA complexes.

MP2 and DFT study of IR spectra of TCNE‐methylsubstituted benzene complexes: Is charge transfer important?

“…Some observed discrepancies (e.g., in reaction enthalpy, dipole moment, IR modes, etc.) between theoretical and experimental data for HMB-TCNE [5,6,9] can be partly explained by the overestimated interplanar distance in the complex obtained at the HF and DFT levels. As it follows from previous studies on stacking complexes [12][13][14], for proper description of the dispersion interactions in these complexes, the proper inclusion of the electron correlation (EC) effects seems to be crucial.…”

“…This rather important finding might be connected with donor-acceptor interplanar distances, which is, consequently, related to the amount of transferred electronic charge from methylated benzenes to TCNE acceptor. This point has been discussed in detail in experimental [4,5] and in our previous theoretical article [9]. In our preceding article [9], we have also shown that because of the solvent effects, the interplanar distance HMB-TCNE is enlarged by 0.2-0.3 ϫ 10 Ϫ10 m compared with that calculated in gas phase.…”

“…The computational strategy was based on our previous experience with theoretical studies of -EDA complexes [9,12,13]. Geometry optimizations, calculation of both harmonic and anharmonic vibrational modes, the interaction energy (including its decomposition), and electric properties for methylbenzenes-tetracyanoethylene (NMB-TCNE) complexes in gas phase have been performed at the MP2 and partly also at the DFT levels using the 6-31G(d) and 6-311G** basis sets.…”

“…As it follows from previous studies on stacking complexes [12][13][14], for proper description of the dispersion interactions in these complexes, the proper inclusion of the electron correlation (EC) effects seems to be crucial. In our recent article [9], we made a detail study on thermodynamics, IR spectra, and some electric properties of the HMB-TCNE complex. On the basis of this experience, we exploited in this study the second-order Møller-Plesset (MP2), standard B3LYP levels as well as a recently introduced DFT-D (dispersion) approach [15][16][17][18].…”

A Computational Study of the Succinimide Derivative Surfactant

“…with values typical for hydrogen bonds [20]. The strong binding site of the molecule is an alcohol group (-OH) which provides the hydrogen bonds of the same strength (at around 1.529-1.552 Å) that is even stronger then could be formed between water molecules (1.537 -1.834 Å).…”