Indirect Nuclear Spin-Spin Exchange Coupling through Solvated Electron in Small Sizes of Cyclic and Cage-Shaped Perfluoroalkanes.

Abstract

Small perfluorocycloalkanes (hexafluorocyclopropane (c-C3 F6 ), octafluorocyclobutane (c-C4 F8 ) and decafluorocyclopentane (c-C5 F10 ) and cage-shaped perfluoroalkanes (perfluoro tetrahedral alkane (C4 F4 ), perfluoro prismane (C6 F6 ) and perfluoro cubane (C8 F8 )) are better electron scavengers. The captured excess electrons are weakly bound inside their backbone voids or over their backbones, forming the solvated electron ( ) systems (e@c-Cn F2n s (n=3, 4, 5) and e@Cn Fn (n=4, 6, 8)). There have been many studies on the structures and properties of such systems. However, the effect of on the indirect nuclear spin-spin coupling (J-coupling) is unknown. In this work, we explore how affects Ne J-coupling between two coupled F nuclei (Ne JFF -coupling) in perfluoroalkane systems through density functional theory calculations. We find unusual trans-Ne JFF -couplings (two coupled F nuclei in trans-position) in e@c-Cn F2n (n=3, 4, 5) and Ne JFF -couplings in e@Cn Fn (n=4, 6, 8). One excess electron not only changes the molecular structures, but also enforces unique distributions and properties, depending on the structural characteristics. We also confirm that such unusual Ne JFF -couplings are realized by through- (T-SE) transmission mechanism, rather than the conventional through-bonds (T-B)/through-space (T-S) ones. The novel transmission mechanism consists of the T-SE coupling path (path 1) and -enhanced T-B T-S coupling path (path 2), and the two paths jointly control Ne JFF through cooperation and competition. Interestingly, the former plays a dominant role for long-range Ne JFF -coupling (N=5), while the latter plays a role in the short-range Ne JFF -coupling (N=3, 4). Path bending angle mainly influences path 1, while path 2 is mainly influenced by the path length. This work not only provides novel insights into the mediating role of in the coupling information exchange, but also proposes a new -based coupling mechanism, possibly opening up potential applications for the -based indirect nuclear spin couplings.