 |
Theoretical study of solvent effect on π-EDA complexation II. Complex between TCNE and two benzene molecules
Kysel’, O., Juhász, G., Mach, P. and Košík, G. Theoretical study of solvent effect on π-EDA complexation II. Complex between TCNE and two benzene molecules Chemical Papers, Vol.61, No. 1, 2007, 66-72
|
|
|
Document type:
|
Článok z časopisu / Journal Article |
|
Collection:
|
Chemical papers
|
|
| Author(s) |
Kysel’, O.
Juhász, G.
Mach, P.
Košík, G.
|
| Title |
Theoretical study of solvent effect on π-EDA complexation II. Complex between TCNE and two benzene molecules
|
| Journal name |
Chemical Papers
|
| Publication date |
2007
|
| Year available |
2007
|
| Volume number |
61
|
| Issue number |
1
|
| ISSN |
0366-6352
|
| Start page |
66
|
| End page |
72
|
| Place of publication |
Poland
|
| Publisher |
Versita
|
| Collection year |
2007
|
| Language |
english
|
| Subject |
250000 Chemical Sciences
250300 Organic Chemistry
|
| Abstract/Summary |
Formation of tetracyanoethylene—benzene 1: 1 and 1: 2 complexes was modeled using the Møller—Plesset second-order theory (MP2) and polarized continuum model (PCM). The MP2 calculated geometry of 1: 1 complex presents a plane-parallel C 2υ sandwich structure with interplanar distance 3.05 × 10−10 m, while the 1: 2 complex has D 2h geometry where the planparallel distance is equal to 3.09 × 10−10 m. The MP2 calculations indicate that the main part of formation enthalpy in both complexes is dispersion energy due to intermolecular electron correlation. The calculations also show that the formation entropy destabilizes both complexes since from the two constituent molecules one complex molecule arises. The MP2/6-31G* procedure showed to be a suitable tool for the estimation of the relative importance of 1: 2 complexation compared to the 1: 1 complexation. In the gas phase the ratio of the equilibrium constants of both complexes K 1:2/K 1:1 = 0.09 was calculated. The presence of solvent, treated by the PCM, further destabilized the 1: 2 complex with respect to the 1: 1 complex. The ratio K 1:2/K 1:1 in CH2Cl2 calculated by the PCM method was 0.022, i.e. the 1: 2 complex was almost 50 times less stable than the 1: 1 complex, which is in agreement with available experimental data. According to the calculations, solvent always destabilizes complex with respect to the isolated (solvated) components. It was also found that charge polarization in the 1: 2 complex with respect to that in the 1: 1 complex was not strictly additive due to the presence of the second benzene molecule in the 1: 2 complex. Non-additive were also formation enthalpy, entropy, polarizability, charge transfer from donors to acceptor molecule and other properties. This fact is caused by a slightly changed interaction between constituent molecules in the 1: 2 complex in comparison with the 1: 1 complex as well as by the interaction between benzene molecules in the 1: 2 complex which is missing in the 1: 1 complex. Preliminary CIS/6-31G* theoretical study regarding a few first-electron (electron charge transfer) transitions in both complexes indicates the presence of Frenkel excitn and Davydov transition energy splitting in the 1: 2 “supercomplex” with the first allowed π → π* absorption transition at λ = 355 nm, while the first allowed transition in the case of 1: 1 complex was characterized by λ = 392 nm with the oscillator strength only half of that of the 1: 2 complex, which is in agreement with experiment. These unexpected large hypso-and hypochromic effects predicted by the theory could allow to overcome difficulties of the experimental determination of the 1: 2 complexation.
|
|
|
