Optically Detected ESR and Low Magnetic Field Signals from Spin Triads:  2-Imidazoline-1-Oxyl Derivatives in X-irradiated Alkane Liquids as a Method to Study Three-Spin Systems

Abstract

This contribution reports the design and synthesis of a series of spin-labeled charge acceptors to produce three-spin systems of "radical ion/biradical ion" type in X-irradiated alkane liquids. This opens the way to study spin triads in experimental conditions, in which short-lived radical ion pairs are conventionally studied, thus offering optically detected techniques such as magneto-resonance OD ESR and level-crossing MARY spectroscopy. The structure of the synthesized 2-imidazoline-1-oxyl derivatives is A-Sp-R, where A is a positive or negative charge acceptor, R is a stable radical, and Sp is a hydrocarbon bridge. The set of 20+ compounds represent a convenient tool to construct experimental three-spin systems with various properties, e.g. with the "third" spin introduced into one or the other partner of the radical ion pair. The degree of exchange coupling between the two paramagnetic fragments in the biradical ion has been demonstrated to strongly depend on the type of the radical fragment R and the structure of the bridge Sp. As a result, a series of acceptors with systematically reduced exchange interaction has been synthesized, and optimal systems for the observation of low magnetic field effect have been found. In the most favorable case, an OD ESR signal from a spin triad living as short as ca. 100 ns has been registered as a single unresolved line. The exchange integral for this biradical anion (9) was estimated from OD ESR and ESR experiments to be ca. 10(3) G by the order of magnitude, which is much greater than the hyperfine couplings in the biradical ion but much smaller than the thermal energy kT.

New approach to synthesis of nitronyl and imino nitroxides based on SNH methodology

“…X-Band CW ESR spectra were recorded in dilute degassed toluene solutions at room temperature on a Bruker EMX spectrometer and modeled in free package Winsim v.0.96 as described earlier. 25 The magnetochemical experiment was run on an MPMS-5S ("Quantum Design") SQUID magnetometer at temperatures from 2 K to 300 К in a homogeneous external magnetic field of up to 49.5 kOe. The molar magnetic susceptibility χ was calculated using Pascal's additive scheme including diamagnetic corrections.…”

High resolution NMR of free radicals: 13C magic angle spinning of two solid organic free radicals derived from 4,5-dihydro-1H-imidazol-3-oxide-1-oxyl and theoretical calculation of their NMR properties

“…29 The synthesis of 4,4,5,5-tetramethyl-2-(1H-pyrazol-3(5)-yl)-2-imidazoline-1-oxyl-3-oxide 3 was described by some of us. 8 Finally, 4,4,5,5-tetramethyl-2-(1H-pyrazol-4-yl)-2-imidazoline-1-oxyl-3-oxide 4 was prepared by Catala, Feher, Amabilino, Wurst and Veciana. 2 Solid state NMR 13 C (100.73 MHz) CPMAS NMR spectra were recorded by using a Bruker WB 400 spectrometer at 300 K with a 4 mm DVT probehead.…”

“…1,[3][4][5][6][7][8][9] The X-ray structure of tautomer 3b was described in 2006. 10,11 Another important contribution to pyrazolyl-nitronylnitroxides is that of Catala, Feher, Amabilino, Wurst and Veciana who prepared compound 4.…”

Cascade Reactions of Me3Si‐Substituted Imidazolidine‐1,3‐Diols with PbO2, Including Oxidation of the Corresponding Diol and Subsequent Elimination of the Trimethylsilyl Fragment

“…X-band CW ESR spectra were recorded with a Bruker EMX spectrometer for dilute degassed toluene solutions at room temperature and modeled with the Winsim v.0.96 free package as described earlier. [13] LC-MSD analysis was performed with an Agilent 1100 Series LC-MSD instrument. The system included a binary pump, vacuum degasser, autosampler, thermostatted column compartment, diode array detector, and mass-selective detector in electrospray ionization (ESI) mode.…”