A Uracil-Substituted α-Nitronyl Nitroxide

Abstract

and bInstitut fur Allgemeine Anorg. und Theoret. Chemie. Universitat Innsbruck. A-6020, Innrain 52a, AustriaWe have synthesized and chemically as well as structurally characterized a new a-nitronyl nitroxide. The spin density distribution in this uracil-substituted nitronyl nitroxide Ur-NN was examined as well as its correlation with the molecular structure, together with a study of the formation of aggregates of Ur-NN in solution.

Cytosine–guanine base pairing in a hydrogen-bonded complex of stable open-shell molecules with S = 1 spins

“…Several examples have been found in which stable radicals of nitroxide are introduced to nucleobases in crystalline solid states. [3][4][5][6] Solution chemistry and ESR spectroscopy have been reported for spin-labeled nucleosides and nucleotides. 7,8 In this study, we have synthesized an open-shell substituted heteromolecular complex of cytosine (1) and guanine (2) derivatives (Scheme 1).…”

Three‐Dimensional Six‐Connecting Organic Building Blocks Based on Polychlorotriphenylmethyl Units—Synthesis, Self‐Assembly, and Magnetic Properties

“…Other examples include the series of dithiadiazolyl and dithiazolyl radicals, which exhibit bulk magnetic order and room temperature bistability 11. Nevertheless, the family of open‐shell tectons most widely used up to now is that of α‐nitronyl nitroxide, α‐imino nitroxide, or tert ‐butyl nitroxide derivatives, because of their high stabilities and the abilities of their nitroxide groups to act as hydrogen‐bond acceptors, so the self‐assembly of such nitroxide‐based building blocks substituted with one or several hydrogen‐bond donors, such as phenol,12 boronic acid,13 imidazole,14 benzimidazole,15 triazole,16 uracil,17 pyrazole,18 phenylacetylene,19 or benzoic acid20, has been extensively studied. The resulting synthons enable both structural control and transmission of magnetic interactions between the radical molecules through strong (OH⋅⋅⋅O) or weak (CH 3 ⋅⋅⋅O) hydrogen bonds 12.…”

“…However, the difficulties lie in determining the exact strength and the nature of the magnetic interactions through the supramolecular pathways, as additional undesired intermolecular through‐space interactions are often present in the solid state and very frequently obstruct proper design of magnetic exchange pathways 12e. 17, 18 …”

Molecular recognition for stable organic radicals ? 2-(6-uradinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxylElectronic supplementary information (ESI) available: synthesis details for 1 and 2; IR data; spin density computations for 2. See http://www.rsc.org/suppdata/cc/b3/b302901h/

“…The use of hydrogen-bonding as a crystal-engineering scaffold has been utilized in a number of cases to attempt to control the solid state intermolecular exchange interactions of organic free radicals. 1 In an example using a biology-inspired motif, Veciana et al, 2 described the synthesis, crystal analysis, and magnetic properties of 2-(5-uradinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxide-3-oxyl (5-Ur-NN, 1). Only a small amount of spin density was observed on the uradinyl ring in 1.…”

“…We note that UV-vis based evidence of some form of aggregation has also been reported for 1. 2 Crystallographically, 2 is much flatter than 1, with a biannular dihedral angle of only 14.5° due to an internal N(2)-H…O(3)-N(3) hydrogen bond from the uradinyl to the iminoylnitroxide moiety (dashed bond, Fig. 1).…”