Abstract
Through-bond interacting organic polyradicals, rendered by customizable capacities of the state-of-the-art synthetic routes, are ideal systems to investigate spin topologies. Relying on Rajca and co-workers' synthetic efforts, hereby we investigate the role of borders in the stability of the high-spin ground state in a series of realistic linear and ring-like arylmethyl polyradical derivatives. We show that, compared to their linear counterpart, the absence of borders in a ring-like arrangement of arylmethyl radicals imposes a larger number of spin-alternation rule violations, which strongly stabilizes the high-spin ground state. In addition, the structural flexibility of the investigated compounds translates into the existence of various structural energy minima for which the ferromagnetic ground state is always maintained. In view of the present results we propose these rings as possible candidates for the development of enhanced high spin single molecule toroics.
Highlights
Ever since the synthesis of the triphenylmethyl radical by Gomberg,[1] carbon-based p-conjugated polyradicals interacting through-bond have been considered as candidates for the practical realization of purely organic magnetism
This follows from the fact that this type of antiferromagnetic solution (AFM) solution involves the minimum amount of spin alternation rule violations
The present study shows that structurally stable, ring-like molecules derived from arylmethyl polyradicals display largely stabilized high-spin ground states as compared to their linearlike counterparts
Summary
Ever since the synthesis of the triphenylmethyl radical by Gomberg,[1] carbon-based p-conjugated polyradicals interacting through-bond have been considered as candidates for the practical realization of purely organic magnetism. Edges in these high-spin ground state linear-like systems plays a detrimental role in ferromagnetism. The most relevant example is precisely the tetraradical that led Rajca and co-workers to coin the spin cluster term.[45] Despite their success, no further attempts have been reported to achieve more extended rings with a larger number of interacting radical centres, as the interest shifted towards the linkage of the tetraradical ring units.[7] Other unrelated approaches consist of planar systems where the polyradical character arises from an equilibrium between quinoidal and aromatic forms,[46,47] and of circular covalent organic frameworks (COFs) to which stable nitronyl radicals are covalently bound.[48] Of particular significance for the present work is the concept of single molecule toroics (SMT),[32] where on top of exchange interactions between centres, having a significant magnetic anisotropy is a key goal. Through a systematic theoretical study of their structural and magnetic features, we provide compelling evidence that a ring-like arrangement persistently presents comparatively more stable high-spin ground states, which is not affected by the ease to undergo conformational distortions. The chemical stability of the investigated examples could be largely increased by promoting a favourable balance between steric protection and the associated strain
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