Tuning of the nitronyl nitroxide radical magnetic and electronic properties by inclusion in cucurbit[n]urils

A nitronyl nitroxide, 2-(benzimidazolyl)-4,4,5,5,-tetramethylimidazolidinyl-3-oxide-1-oxy, 1 and its imino nitroxide analog 2, have been included in cucurbit[n]urils, CBn (n = 7,8), as their hydrochlorides and neutral compounds as well. The hydrochlorides form soluble 1:1 complexes. In the solid state the paramagnetic centers are well isolated and magnetic interactions are cancelled out in contrast to what is observed for the pure nitroxides. The two inclusion complexes involving 1 were characterized by X-ray crystallography. When they were heated in the solid state, one observed a clean conversion of the nitronyl nitroxide guest, 1, into its analog 2.

Graphical abstractThe hydrochlorides of 2-(2-benzimidazolyl)-4,4,5,5-tetramethylimidazolidinyl-3-oxide-1-oxy, 1 and of its imino nitroxide analog 2, form 1:1 inclusion compounds with cucurbit[n]urils (CB, n = 7,8). In the solid state both inclusion complexes of 1·HCl are converted into those of 2·HCl on heating (150–200 °C). While the included paramagnetic hydrochlorides are magnetically isolated, in the complexes obtained from neutral free radicals and CB8, which have a 2:3 composition, interacting guests lead to a triplet ground spin-state.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Nitronyl and imino nitroxide hydrochlorides are included in cucurbit[n]urils. ► Crystalline inclusion complexes have the following composition – Rad.HCl@CBn. ► Heating of Inclusion compounds converts nytronyl nitroxide into imino nitroxide. ► Neutral radicals are included giving (Rad)2@(CB8)3 with a triplet ground spin-state.