X-ray diffraction, inelastic neutron scattering (INS) and infrared (IR) studies on 2:1 hexamethylbenzene (HMB)–tetracyanoethylene (TCNE) complex

Pawlukojć, A.; Sawka‐Dobrowolska, W.; Bator, G.; Sobczyk, L.; Grech, E.; Nowicka‐Scheibe, J.

doi:10.1016/j.chemphys.2006.05.003

Cited by 12 publications

(25 citation statements)

References 30 publications

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“…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.…”

Section: Introductionmentioning

confidence: 73%

“…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.…”

mentioning

confidence: 77%

“…Here, we mention that electron transfer from donor to acceptor is mainly because of the interaction between -HOMO of donor with *-lowest unoccupied molecular orbital (LUMO) on TCNE. Because LUMO orbital has a node on C'N connections, its partial occupation Number of methyl groups solid state (3.16 -3.26 ϫ 10 Ϫ10 m) [5,10]. B3LYP charges transferred from NMB to TCNE are also lower than those calculated by MP2 (Fig.…”

mentioning

confidence: 92%

“…Recent precise measurements of CN stretching and terahertz INS vibration frequencies for a complete series of methylbenzenes-TCNE complexes [4,5] motivated us to make a detail theoretical study with an interpretation of these vibrations and their dependencies on the number of methyl groups N. Of course, for the N Ͼ 1, there exist more positional isomers (i.e., for N ϭ 2, these are o-, m-, and pxylenes). In such cases, we used either the most symmetrical one or the same isomers as in experimental studies.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, several detailed theoretical and experimental studies [4 -10] of hexamethylbenzene-tetracyanoethylene (HMB-TCNE) complex have been focused on measurements and interpretation of its vibrational spectra, predominantly in crystals of 1:1 and 2:1 stoichiometry [8]. The inelastic neutron scattering (INS) technique as a new and powerful method for measuring low (e.g., terahertz) frequency vibrational modes as well as the classical IR spectroscopy and density functional theoretical (DFT) approaches have also been applied [5]. The HMB-TCNE complex in CCl 4 has been studied in connection with elucidation of the photophysical processes such as photoabsorption, fluorescence emission, and radiationless transition in the lowest excited singlet state [11].…”

Section: Introductionmentioning

confidence: 99%

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

Kyseľ

Budzák

Mach

et al. 2009

Int J of Quantum Chemistry

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ABSTRACT:The second-order Møller-Plesset (MP2) and density functional theory (DFT; B3LYP, B3LYP-D) approaches show that the CN (and also CAC) stretching IR vibrations are relatively small but reproducibly shifted to lower frequencies in a series of methylbenzenes-tetracyanoethylene (NMB-TCNE, N ϭ mono-, di-, …, hexa-) complexes with increasing number of methyl groups (N). These CN stretching IR frequency shifts, ranging from 8 to 12 cm Ϫ1 , are linearly dependent on number N but still 2-4 times greater than recently published experimental data [Stires et al., Chem Commun, 2005, 28, 3532; Pawlukojc et al., Chem Phys, 2006, 327, 311]. An explanation of the shifts toward lower frequencies is in literature [Stires et al., Chem Commun, 2005, 28, 3532; Pawlukojc et al., Chem Phys, 2006, 327, 311] usually attributed to the magnitude of transferred electron charge ⌬Q from a donor molecule to TCNE (mainly to its LUMO [lowest unoccupied molecular orbital]). The LUMO has antibonding character on CN and CAC bonds, and thus the respective CN and CAC bond orders are, due to partial occupation in the complex, decreased. However, the difference by a factor of 2-4 between our MP2 (and also B3LYP) calculations and experiment is probably also due to the effect of environment, i.e., intermolecular forces between complex and solvent molecules or crystal lattice. The calculated interplanar distance R, dipole moment , and transferred charge ⌬Q are approximately linearly dependent on number of methyl groups N. However, between N ϭ 2 and 3, the abrupt changes in the dependencies were observed. This is caused by the change of mutual (perpendicular) orientations between respective methyl benzenes and TCNE in the complexes as a consequence of preferred interaction between one of two degenerated or near degenerated highest occupied molecular orbitals (being orthogonal) on NMB with LUMO located mainly on TCNE. This fact is important for many properties (especially for electron excited states) of these complexes. A strong dependence of polarizability, namely of its ␣ zz part, of the benzene-TCNE (Be-TCNE) complex on soft vibrations was found. The vibrational contribution to ␣ zz value is almost as large as the electronic ␣ zz contribution. Finally, MP2 and B3LYP studies indicate that inclusion of anharmonicity has small, if any, effect on calculated vibrational frequencies of Be-TCNE. This theoretical finding is quite important especially because it holds also for soft vibrational modes, which are always present at weak intermolecular complexes.

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Section: Introductionmentioning

confidence: 73%

mentioning

confidence: 77%

mentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Kyseľ

Budzák

Mach

et al. 2009

Int J of Quantum Chemistry

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

Kyseľ

Budzák

Medveď

et al. 2008

Int J of Quantum Chemistry

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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.

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Theoretical analysis of charge-transfer electronic spectra of methylated benzenes—TCNE complexes including solvent effects: approaching experiment

et al. 2012

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X-ray diffraction, inelastic neutron scattering (INS) and infrared (IR) studies on 2:1 hexamethylbenzene (HMB)–tetracyanoethylene (TCNE) complex

Cited by 12 publications

References 30 publications

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

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

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

Theoretical analysis of charge-transfer electronic spectra of methylated benzenes—TCNE complexes including solvent effects: approaching experiment

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