Charge Transfer Complexes Formed by Heterocyclic Thioamides and Tetracyanoethylene: Experimental and Theoretical Study

Tatiana S Kolesnikova; Margarita S Chernov'yants; Mikhail E Kletskii; Oleg N Burov; Gennady I Bondarenko; Pavel A Knyazev

doi:10.1021/acs.jpca.7b00564

Charge Transfer Complexes Formed by Heterocyclic Thioamides and Tetracyanoethylene: Experimental and Theoretical Study

J Phys Chem A. 2017 Sep 21;121(37):7000-7008. doi: 10.1021/acs.jpca.7b00564. Epub 2017 Sep 12.

Authors

Tatiana S Kolesnikova¹, Margarita S Chernov'yants¹, Mikhail E Kletskii¹, Oleg N Burov¹, Gennady I Bondarenko¹, Pavel A Knyazev²

Affiliations

¹ Chemical Department, Southern Federal University , Zorge st. 7, Rostov-on-Don 344090, Russia.
² Institute of Physical and Organic Chemistry, Southern Federal University , Stachki av,194/2, Rostov-on-Don 344092, Russia.

PMID: 28849931
DOI: 10.1021/acs.jpca.7b00564

Abstract

Tetracyanoethylene (TCNE) as one of the most versatile organic compounds is involved in various chemical reactions with electron transfer. Charge transfer complexes (CTCs) of a few antioxidants, nitrogen containing thioamides [pyrrolidine-2-thione (I), 1,3-H-imidazolidine-2-thione (II), 1,3-H-Imidazoline-2-thione (III), pyridine-2-thione (IV), 5-trifluoromethylpyridine-2-thione (V), 4-trifluoromethylpyrimidine-2-thione (VI), quinoline-2-thione (VII), 3,4,5,6-tetrahydropyrimidine-2-thione (VIII)] as π-donors and TCNE as π-acceptor were studied. The DFT PCM/UB3LYP/6-31++G(d,p) and SA-CASSCF quantum chemical calculations were used to study the structures and relative stabilities of these complexes in the ground and lowest excited electronic states. The formation of a weak molecular associates in the chloroform and acetonitrile solutions was confirmed by UV/vis and IR absorption spectroscopy. The stability constants and molar extinction coefficients were estimated by UV/vis spectroscopy. The highest stability in acetonitrile is found for associates formed by quinoline-2-thione and pyridine-2-thione with TCNE, the lowest one is found for CTC formed by imidazolidine-2-thione. Molecular associate formed by pyridine-2-thione and TCNE has the greatest stability in the chloroform solution. 5-Trifluoromethylpyridine-2-thione and 4-trifluoromethylpyrimidine-2-thione do not form CTC in CH₃CN due to the presence of an electron acceptor group in the molecules. The molar extinction values of CTC vary within the range of 0.4 × 10³ to 1.0 × 10⁴ M^-1 cm^-1. An analytical strategy of thioamides identification based on wavelength and intensity of CTCs absorption band has been suggested.