A λ⁵‐cylotriphosphazene with nitroxyl groups as model for a paramagnetic poly(organo‐λ⁵‐phosphazene)

Abstract

Reaction of hexachlorocyclotriphosphazene (syst. name: 2,2,4,4,6,6-hexachloro-l,3,5,21', 4h' ,6XS-triazatriphosphorine) (1) with 4-hydroxy-2,2,6,6-tetramethylpiperidin-l -oxyl(2 a) gave the hexa-substituted h'-cyclotriphosphazene 3 a. Electron paramagnetic resonance spectra at low concentrations (lo-' mol/L) showed a singlet only (no triplet) due to spin-spin exchange in the molecule. The paramagnetic molar susceptibility amounts to 7229.cm3/mol at 300 K and does not depend on the magnetic field strength. 3a obeyed the Curie-Weiss law between 36 and 296 K demonstrating that there is no antiferromagnetic spin exchange.

Synthesis and Straightforward Quantification Methods of Imino Nitroxide-Based Hexaradical Architecture on a Cyclotriphosphazene Scaffold

“…Special interest was devoted to the synthesis of dendrimeric multiradicals with nitroxides as end groups with the purpose of spin trapping for nitric oxide and contrasting agents in magnetic resonance imaging (MRI). Among the dendrimeric structures, the cyclotriphosphazene core provides a unique platform to be partially − or completely − functionalized by incorporating radical moieties depending on the needs of application. Studies on cyclotriphosphazene core multiradicals were mostly − devoted to EPR and magnetic analysis.…”

“…Among the dendrimeric structures, the cyclotriphosphazene core provides a unique platform to be partially − or completely − functionalized by incorporating radical moieties depending on the needs of application. Studies on cyclotriphosphazene core multiradicals were mostly − devoted to EPR and magnetic analysis. Even if nitroxide radicals are well-known to be redox-active species, no studies filling electrochemical characterization of nitroxide–cyclotriphosphazene hybrid compounds were published yet.…”

Polyphosphorhydrazone-Based Radical Dendrimers

“…The first articles published of this kind of dendrimer with radicals were based only on a cyclotriphosphazene ring as a scaffold for the radicals in order to study its magnetic, electrochemical, and structural properties, the interaction between radicals at the dendrimer surface, as well as the obtaining of chiral multi-spin systems [18,[33][34][35][36][37][38]. For example, it was possible to provide, for the first time, experimental data about the molecular structure in solution, by EPR, of the cyclotriphosphazene ring functionalized with TEMPO radicals in its six branches, demonstrating they have the same relative orientation as in the solid state determined by X-ray diffraction: three branches above the cyclotriphosphazene ring and the other three below it (Figure 1) [18].…”