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High‐spin organic tetraradicals with significant intramolecular exchange interactions have high potential for advanced technological applications and fundamental research, but those synthesized to date possess limited stability and processability. In this work, we have designed a tetraradical based on the Blatter's radical and nitronyl nitroxide radical moieties and successfully synthesized it by using the palladium‐catalyzed cross‐coupling reaction of a triiodo‐derivative of the 1,2,4‐benzotriazinyl radical with gold(I) nitronyl nitroxide‐2‐ide complex in the presence of a newly developed efficient catalytic system. The molecular and crystal structure of the tetraradical was confirmed by X‐ray diffraction analysis. The tetraradical possesses good thermal stability with decomposition onset at ∼150 °C under an inert atmosphere and exhibits reversible redox waves at −0.54 and 0.45 V versus Ag/AgCl. The magnetic properties of the tetraradical were characterized by SQUID magnetometry of polycrystalline powders and EPR spectroscopy in various matrices. The collected data, analyzed by using high‐level quantum chemical calculations, confirmed that the tetraradical has a triplet ground state and a nearby excited quintet state. The unique high stability of the prepared triazinyl‐nitronylnitroxide tetraradical is a new milestone in the field of creating high‐spin systems. [ABSTRACT FROM AUTHOR]

Sterically encumbered bis(m‐terphenyl)chalcogenides, (2,6‐Mes2C6H3)2E (E=S, Se, Te) were obtained by the reaction of the chalcogen tetrafluorides, EF4, with three equivalents of m‐terphenyl lithium, 2,6‐Mes2C6H3Li. The single‐electron oxidation of (2,6‐Mes2C6H3)2Te using XeF2/K[B(C6F5)4] afforded the radical cation [(2,6‐Mes2C6H3)2Te][B(C6F5)4] that was isolated and fully characterized. The electrochemical oxidation of the lighter homologs (2,6‐Mes2C6H3)2E (E=S, Se) was irreversible and impaired by rapid decomposition. [ABSTRACT FROM AUTHOR]

[TCNE].− (TCNE=tetracyanoethylene) has been isolated as D2 h π-[TCNE]22− possessing a long, 2.9 Å multicenter 2-electron-4-center (2e−/4c) C−C bond, and as C2 π-[TCNE]22− possessing a longer, 3.04 Å multicenter 2e−/6c (4 C+2 N atoms) bond. Temperature-dependent UV/Vis spectroscopic measurements in 2-methyltetrahydrofuran (MeTHF) has led to the determination of the dimerization, 2[TCNE].−⇌π-[TCNE]22−, equilibrium constants, Keq( T), [[TCNE]22−]/[[TCNE].−]2, enthalpy, Δ H, and entropy, Δ S, of dimerization for [Mepy]2[TCNE]2 (Mepy= N-methylpyridinium, H3CNC5H5+) possessing D2 h π-[TCNE]22− and [NMe4]2[TCNE]2 possessing C2 π-[TCNE]22− conformations in the solid state; however, both form D2 h π-[TCNE]22− in MeTHF solution. Based on Δ H=−3.6±0.1 kcal mol−1 (−15.2 kJ mol−1), and Δ S=−11±1 eu (−47 J mol−1 K−1) and Δ H=−2.4±0.2 kcal mol−1 (−10.2 kJ mol−1), and Δ S=−8±1 eu (−32 J mol−1 K−1) in MeTHF for [NMe4]2[TCNE]2 and [Mepy]2[TCNE]2, respectively, the calculated Keq(298 K) are 1.6 and 1.3 m−1, respectively. The observed Keq (145 K) are 3 and 2 orders of magnitude greater for [NMe4]2[TCNE]2 and [Mepy]2[TCNE]2, respectively. The Keq(130 K) is 4470, 257, ≈0.8, and ≪0.1 m−1 for [NMe4]2[TCNE]2, [Mepy]2[TCNE]2, [NEt4]2[TCNE]2, and [N( nBu)4]2[TCNE]2, respectively, decreasing with increasing cation size. At standard conditions and below ambient temperature the equilibrium favors the dimer for the NMe4+ and Mepy+ cations. From the decreasing enthalpy, NMe4+>Mepy+, along with the decrease in dimer formation Keq( T) as NMe4+>Mepy+>NEt4+>N( nBu)4+, the dimer bond energy decreases with increasing cation size in MeTHF. This is attributed to a decrease in the [A]+⋅⋅⋅[TCNE]− attractive interactions with increasing cation size. Solid state UV/Vis spectroscopic determinations of [NMe4]2[TCNE]2 are reported and compared to D2 h π-[TCNE]22− conformers. The feasibility and limitations of temperature-dependent electron paramagnetic resonance (EPR) measurements for the determination of Keq( T) are also discussed. [ABSTRACT FROM AUTHOR]

It was shown that dipole-stabilized paramagnetic carbanion lithiated 4,4,5,5-tetramethyl-4,5-dihydro-1 H-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 2 H-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(14N)=[0.260 0.260 1.625] mT, two equivalent tensors for the nitronyl nitroxide moiety a(14N)=[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. [ABSTRACT FROM AUTHOR]

Spin-labelled compounds are widely used in chemistry, physics, biology and the materials sciences but the synthesis of stable high-spin organic molecules is still a challenge. We succeeded in synthesising heteroatom analogues of the 1,1,2,3,3-pentamethylenepropane (PMP) diradicals with two nitronyl nitroxide ( DR1) and with two iminonitroxide ( DR2) fragments linked through the C(sp2) atom of the nitrone group. According to magnetic susceptibility measurements, EPR data and ab initio calculations at the (8,6)CASSCF and (8,6)NEVPT2 levels, DR1 and DR2 have singlet ground states. The singlet-triplet energy splitting (2 J) is low ( J/ k=−7.4 for DR1 and −6.0 K for DR2), which comes from the disjoint nature of these diradicals. The reaction of [Cu(hfac)2] with DR1 gives rise to different heterospin complexes in which the diradical acts as a rigid ligand, retaining its initial conformation. For the [{Cu(hfac)2}2( DR1)(H2O)] complex, sufficiently strong ferromagnetic interactions ( J1/ k=42.7 and J2/ k=14.1 K) between two coordinating CuII ions and DR1 were revealed. In [{Cu(hfac)2}2( DR1)(H2O)][Cu(hfac)2(H2O)], the very strong and antiferromagnetic ( J/ k=−416.1 K) exchange interaction between one of the coordinating CuII ions and DR1 is caused by the very short equatorial CuO bond length (1.962 Å). [ABSTRACT FROM AUTHOR]