Computational investigations of intermolecular interactions between electron-accepting bromo- and iodo-pentafluorobenzene and electron-donating furan and thiophene

Abstract

Bromo- and iodo-pentafluorobenzene (C₆F₅X, X = Br, I) exhibit intriguing σ- and π-hole characters, which are able to accept electrons, whereas furan (C₄H₄O) and thiophene (C₄H₄S) are able to donate electrons because of their electron-rich atoms and groups (i.e., the O atom and π-ring in C₄H₄O and the π-ring in C₄H₄S). Theoretical investigations of intermolecular interactions in these systems (i.e., C₄H₄O and C₆F₅Br, C₄H₄S and C₆F₅Br, C₄H₄O and C₆F₅I, and C₄H₄S and C₆F₅I) have been carried out at the M06-2X/aug-cc-pVDZ and wB97-XD/aug-cc-pVDZ levels with and without the counterpoise method, together with single-point calculations at the CCSD(T)/aug-cc-pVDZ level. For the system of C₄H₄O and C₆F₅X (X = Br, I), five different dimers, namely, I–V and I′–V′, which are connected by σ-hole⋯n, σ-hole⋯π and π-hole⋯π bonds, were found. Moreover, for the system of C₄H₄S and C₆F₅Br, four different dimers, namely, VI–IX, which are connected by σ-hole⋯π and π-hole⋯π bonds, were found. However, five dimers, namely, VI′–X′, were found for the system of C₄H₄S and C₆F₅I, which are connected by σ-hole⋯π, π-hole⋯π and σ-hole⋯n bonds. The driving forces for the formation of these dimers were revealed by EDA analyses. NCI, QTAIM and NBO analyses were employed to prove the existence of intermolecular interactions in these dimers and to elucidate their nature. The results presented here will be insightful for the study of other intermolecular systems that involve σ- and π-holes.