Inclusion of a nitronyl nitroxyl radical and its hydrochloride in cucurbit[8]uril

摘要

The recognition properties of cucurbit[8]uril (CB8) toward nitronyl nitroxide 2-(2-benzimidazolyl)-4,4,5,5-tetramethylimidazolidinyl-3-oxide-1-oxy (1) and its hydrochloride have been investigated. 1·HCl led to 1:1 inclusion complex [1·HCl@CB8], which was characterized both in solution and by single-crystal X-ray diffraction. In this compound only the tetramethylimidazolidinyl fragment is included in the host. The magnetic behavior of the complex corresponds to a Curie law with a large separation of the spin carriers in the solid. In contrast, an insoluble species exhibiting ferromagnetic behavior is formed when pure 1 reacts with acid-free CB8. The formula [(1)_2 at (CB8)_3], in which two radical guests are arranged in such a way that the phenyl groups of the benzimidazolyl substituents are both stacked into one CB8 and the tetramethyl fragments are each capped by a terminal macrocycle, is proposed, in agreement with microanalysis, spectrophotometric, EPR, and magnetic measurements. According to McConnell's rules, the alternating spin densities within the stacked aromatic fragments result in a ferromagnetic interaction (J=+2.3 cm~(-1), H=-2JS _1S_2) and a triplet ground spin state for the inclusion complex. Paramagnetic inclusion complexes: Recognition of 2-(2-benzimidazolyl)- 4,4,5,5-tetramethylimidazolidinyl-3-oxide-1-oxy by cucurbit[8]uril has been investigated. The hydrochloride of this nitronyl nitroxide radical forms a 1:1 complex, whereas the neutral nitronyl nitroxide forms a supramolecular species involving three hosts and two radical guests (see figure; C cyan, H white, N red, O blue) with a triplet ground spin state.