A Crystallographic Study of a Novel Tetrazolyl-Substituted Nitronyl Nitroxide Radical

Vasily Romanov,Dominique Luneau,Elena Zaytseva,Irina Bagryanskaya,Nina Gritsan,Dmitry Gorbunov,Evgeny Tretyakov

doi:10.3390/cryst8090334

Abstract

Spin-labelled compounds are widely used in chemistry, physics, biology, and material sciences, but the directed synthesis of some functionalized organic radicals is still a challenge. We succeeded in the preparation of a tetrazolyl-substituted nitronyl nitroxide radical in pure crystalline form. According to the single-crystal X-ray data, intra- (NH…O, 2.43 Å) and inter-molecular hydrogen bonds (NH…O, 1.91 Å) are formed between NH groups of the tetrazole cycles and O atoms of the paramagnetic moieties. The intermolecular H-bonds connect the molecules forming chains along the a-axis. Moreover, there are short intermolecular contacts between the O atoms (3.096 Å) and between the O and C atoms (3.096 Å) of the nitronyl nitroxide moieties within the chain. The spin-unrestricted broken-symmetry calculations performed at the BS-UB3LYP/def2-TZVP level of theory predicted a sufficient ferromagnetic interaction (J ≈ 20 cm–1) between the adjacent radicals inside the chain, but a weak antiferromagnetic interaction (−J ≤0.2 cm−1) between the nearest radicals belonging to the different chains. Thus, a rare case when stable radicals, the tetrazolyl-substituted nitronyl nitroxides, are ordered into ferromagnetic chains was revealed; an investigation of the magneto-structural correlations inherent in the nitroxide radical will demand a special experiment in the sub-Kelvin regime.

Highlights

Nitronyl nitroxide radicals and their complexes have been intensively studied for many years, leading to key discoveries in the field of molecular magnetism, such as the preparation of pure organic ferromagnets and ferrimagnets, complexes of transition metals with nitroxides showing magnetic ordering effects, and copper–nitroxide complexes with unusual spin-crossover behavior [1,2,3,4,5,6,7,8,9]
We report the synthesis and crystal structure of neutral tetrazolyl-substituted nitronyl nitroxide 1-H, which can be useful as a ligand for the 1‐H, preparation of layered polymer complexes transition tetrazolyl‐substituted nitronyl nitroxide which can be useful as a ligand for the with preparation of metals (Figure layered polymer complexes with transition metals (Figure 1)
The rare short contacts (3.096 Å) between the oxygen and carbon atoms of the neighboring radicals possessing the spin densities of opposite signs in the pair triplet state were observed [35,36]; this explains sufficient ferromagnetic exchange coupling (J ≈ 20 cm−1 ) between the radicals inside the chain predicted by BS-density functional theory (DFT)

Summary

Introduction

Nitronyl nitroxide radicals and their complexes have been intensively studied for many years, leading to key discoveries in the field of molecular magnetism, such as the preparation of pure organic ferromagnets and ferrimagnets, complexes of transition metals with nitroxides showing magnetic ordering effects, and copper–nitroxide complexes with unusual spin-crossover behavior [1,2,3,4,5,6,7,8,9].This situation has stimulated the subsequent active developments in the chemistry of this class of paramagnetic compounds with an emphasis on the synthesis of their polyfunctional derivatives [10,11,12,13,14,15].to date, a huge number of different nitronyl nitroxides have been successfully obtained, there are still poorly studied but interesting types of organic radicals within this class. Nitronyl nitroxide radicals and their complexes have been intensively studied for many years, leading to key discoveries in the field of molecular magnetism, such as the preparation of pure organic ferromagnets and ferrimagnets, complexes of transition metals with nitroxides showing magnetic ordering effects, and copper–nitroxide complexes with unusual spin-crossover behavior [1,2,3,4,5,6,7,8,9] This situation has stimulated the subsequent active developments in the chemistry of this class of paramagnetic compounds with an emphasis on the synthesis of their polyfunctional derivatives [10,11,12,13,14,15]. We report the synthesis and crystal structure of neutral tetrazolyl-substituted nitronyl nitroxide 1-H, which can be useful as a ligand for the 1‐H, preparation of layered polymer complexes transition tetrazolyl‐substituted nitronyl nitroxide which can be useful as a ligand for the with preparation of metals

Methods

Discussion

Conclusion