On the cation–π capabilities of small all sp²‐carbon host structures. Evaluation of [6.8]₃cyclacene from relativistic DFT calculations

Abstract

Cation–π interactions are noncovalent forces with essential roles in the stability of protein structures, molecular recognition, and host–guest chemistry. In this work, we discuss the formation of cation–π complexes involving one of the smallest characterized nanobelts to date, given [6.8]3cyclacene, by using relativistic DFT‐D calculations. Such nanobelt exhibits a noteworthy all‐sp2 carbon backbone, leading to a rigid and confined host framework. Our results reveal that the inclusion of representative cations, such as Ag+ and Sn2+, appears to be plausible, revealing that it is feasible to obtain these compounds experimentally. Such systems involves two contrasting coordination modes, where the Ag+ cation remains coordinated in the upper face of the nanobelt, whereas the Sn2+ is able to be located at the center of the structure. In addition, the coordination of isoelectronic Cd2+ and In+ was also discussed. Moreover, the bonding characteristics of the resulting cation–π interaction show that the π‐orbitals from the nanobelt 1 are able to moderate the charge transfer, according to the selected cation, which can be seen as an interesting strategy to tune the amount of charge of the π‐backbone in nanobelts. We envisage that the use of more rigid host in the formation of cation–π interactions will be beneficial to gain a better understanding about the metal coordination and also to tune the capabilities of related nanobelts or nanotubes sections.

Theoretical Insights for Materials Properties of Cyclic Organic Nanorings

“…However, minor structural changes (i.e., topological defects) of the CC forms could reduce significantly their radicaloid nature thus allowing their final synthesis. For instance, theoretical studies of annelated pentagon‐heptagon rings (i.e., [5.7] n CCs), [ 138 ] hexagon‐octagon rings (i.e., [6.8] n CCs), [ 139–142 ] or pentagon‐hexagon rings (i.e., [5.5.6] n CCs) [ 143 ] has been shown to lead to closed‐shell systems. Doping with B, N, or Si atoms seems to also increase their synthetic affordability.…”

Main-group metal cyclophane complexes with high coordination numbers

“…21 They further extended the concept to computationally understand the role of formal charge of a cation in p-cation interactions by comparing the complexes of isoelectronic In + and Cd 2+ with pCp. 22 In further instances, Castro et al investigated helicenes 23 and Dp 24 as potential p-donors to form various p-cation interactions through relativistic DFT approach. A review of the use of relativistic computational tools to study the structural and bonding properties of these p-cation interactions has been published recently 25 which shows that different avenues in this eld have been opened by the groups of Castro and Frenking over the last few years.…”