Reaction of Paramagnetic Synthon, Lithiated 4,4,5,5‐Tetramethyl‐4,5‐dihydro‐1H‐imidazol‐1‐oxyl 3‐oxide, with Cyclic Aldonitrones of the Imidazole Series

Abstract

It was shown that dipole-stabilized paramagnetic carbanion lithiated 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide can be attached in a nucleophilic manner to either isolated or conjugated aldonitrones of the 2,5-dihydroimidazole 3-oxide and 2H-imidazole 1-oxide series to afford adducts the subsequent oxidation of which leads to polyfunctional mono- and diradicals. According to XRD, at least two polymorphic modifications can be formed during crystallization of the resulting paramagnetic compounds, and for each of them, geometric parameters of the molecules are similar. An EPR spectrum of the diradical in frozen toluene has a complicated lineshape, which can be fairly well reproduced by using X-ray diffraction structural analysis and the following set of parameters: D=14.9 mT, E=1.7 mT; tensor a((14) N)=[0.260 0.260 1.625] mT, two equivalent tensors for the nitronyl nitroxide moiety a((14) N)=[0.198 0.198 0.700] mT, and g≈2.007. According to our DFT and ab initio calculations, the intramolecular exchange in the diradical is very weak and most likely ferromagnetic.

The Design of Radical Stacks: Nitronyl‐Nitroxide‐Substituted Heteropentacenes

“…The EPR spectra of NN 2 ‐DT m BDT in toluene solution are characteristic of bis(nitronyl nitroxide) systems with a strong (on the energy scale of EPR spectroscopy) intramolecular exchange interaction ( J ), which by far exceeds hyperfine coupling ( J ≫ A N ; Figure ). Indeed, by using the CASSCF and NEVPT2 methods, well‐proven in the calculations of J in diradicals, we predict the | J | value to be on the order of a few K (1 K corresponds to 744 mT). The solution spectrum (Figure ) consists of nine spectral peaks resulting from coupling of two unpaired electrons with four equivalent 14 N nuclei; the exchange interaction results in a distance between the lines that equals half of the HFC constant corresponding to the monoradical moiety | A N |/2≈0.375 mT.…”

Triplet Diradical‐Cation Salts Consisting of the Phenothiazine Radical Cation and a Nitronyl Nitroxide

“…The exchange interaction for the same contact in the gallium salt was the smallest positive value of J calcd-inter =+0.03 K. As stated above,t he DFT calculations usually overestimate the ferromagnetic contributions to the intramolecular J value for diradicals, but are useful to estimate those of intermolecular interactions of diradicals. [25,26] At this level of calculation, av alue smaller than 0.1 Ki sn ot reliable. The FeBr 4 salt has an almost identical intermolecular CÀCc ontact of [···(DAA-PTZ) + ···(DAA-PTZ) + ···] and as mall negative value of J calcd-inter = À1.2 Kw as found (see Ta ble S7).…”

Magnetic Interaction Observed in Hetero Biradical Derivatives Containing a 2,2,5,5‐Tetramethylpyrrolin‐1‐yloxyl Unit as a Localized Spin Center

“…However, the intramolecular magnetic coupling through a non‐conjugated spin center has not yet been elucidated except for a recent computational result . These circumstances prompted us to investigate the magneto‐structural correlation of the hetero biradicals containing the pyrrolinoxyl unit as a localized spin center.…”

“…The estimated spin density distributes not only over nitroxyl moiety andt etramethyl groups but also over vinylic moiety,w hich is in consistentw ith the above EPR studies.However,t he intramolecular magnetic coupling through a non-conjugated spin centerh as not yet been elucidated except for ar ecent computational result. [15] These circumstances prompted us to investigate the magneto-structural correlation of the hetero biradicals containing the pyrrolinoxylu nit as al ocalized spin center. In the presentp aper,t he magnetostructuralc orrelation of an ovel pyrrolinoxyl-verdazyl radical 1 was discussed in connectionw ith that of the knownh etero biradical 2,f irst synthesized by Hideg et al [16] (Figure 2).Single crystals of 1 and 2 suitable for crystallographic analysis wereo btained by slow evaporation.…”