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1. Kinetic Investigations of the CH (X ² Π) Radical Reaction with Cyclopentadiene

   https://doi.org/10.1021/acs.jpca.9b03813  

   Caster, Kacee L.; Donnellan, Zachery N.; Selby, Talitha M.; Goulay, F. (June 2019, The Journal of Physical Chemistry A)
2. Atmospheric Chemistry of HOHg ^(II) O ^• Mimics That of a Hydroxyl Radical

   https://doi.org/10.1021/acs.jpca.3c04159  

   Hewa_Edirappulige, Darshi T; Kirby, Ilena J; Beckett, Camille K; Dibble, Theodore S (October 2023, The Journal of Physical Chemistry A)

   HOHg(II)O•, formed from HOHg(I)• + O3, is a key intermediate in OH-initiated oxidation of Hg(0) in the atmosphere. As no experimental data is available for HOHg(II)O•, we use computational chemistry (CCSD(T)//M06-2X/AVTZ) to characterize its reactions with atmospheric trace gases (NO, NO2, CH4, C2H4, CH2O and CO). In summary, HOHg(II)O•, like the analogous BrHg(II)O• radical, largely mimics the reactivity of •OH in reactions with NOx, alkanes, alkenes, and aldehydes. The rate constant for its reaction with methane (HOHg(II)O• + CH4 → Hg(II)(OH)2 + •CH3) is about four times higher than that of •OH at 298 K. All these reactions maintain mercury as Hg(II), except for HOHg(II)O• + CO → HOHg(I)• + CO2. Considering only the six reactions studied here, we find that reduction by CO dominates the fate of HOHg(II)O• (79-93%) in many air masses (in the stratosphere and at ground level in rural, marine, and polluted urban regions) with only modest competition from HOHg(II)O• + CH4 (<15%). We expect that this work will help global modeling of atmospheric mercury chemistry. 

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3. Thiophene‐Based Double Helices: Radical Cations with SOMO–HOMO Energy Level Inversion ^†

   https://doi.org/10.1111/php.13475  

   Rajca, Andrzej; Shu, Chan; Zhang, Hui; Zhang, Sheng; Wang, Hua; Rajca, Suchada (July 2021, Photochemistry and Photobiology)

   Abstract We report relatively persistent, open‐shell thiophene‐based double helices, radical cations 1^•+‐TMS₁₂and 2^•+‐TMS₈. Closed‐shell neutral double helices, 1‐TMS₁₂and 2‐TMS₈, have nearly identical first oxidation potentials,E^+/0 ≈ +1.33 V, corresponding to reversible oxidation to their radical cations. The radical cations are generated, using tungsten hexachloride in dichloromethane (DCM) as an oxidant,E^+/0 ≈ +1.56 V. EPR spectra consist of a relatively sharp singlet peak with an unusually lowg‐value of 2.001–2.002, thus suggesting exclusive delocalization of spin density over π‐conjugated system consisting of carbon atoms only. DFT computations confirm these findings, as only negligible fraction of spin density is found on sulfur and silicon atoms and the spin density is delocalized over a single tetrathiophene moiety. For radical cation, 1^•+‐TMS₁₂, energy level of the singly occupied molecular orbital (SOMO) lies below the four highest occupied molecular orbitals (HOMOs), thus indicating the SOMO–HOMO inversion (SHI) and therefore, violating the Aufbau principle. 1^•+‐TMS₁₂has a half‐life of the order of only 5 min at room temperature. EPR peak intensity of 2^•+‐TMS₈, which does not show SHI, is practically unchanged over at least 2 h. 

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4. Isolation of the elusive bisbenzimidazole Bbim ³⁻ ˙ radical anion and its employment in a metal complex

   https://doi.org/10.1039/d1sc07245e  

   Benner, Florian; Demir, Selvan (May 2022, Chemical Science)

   The discovery of singular organic radical ligands is a formidable challenge due to high reactivity arising from the unpaired electron. Matching radical ligands with metal ions to engender magnetic coupling is crucial for eliciting preeminent physical properties such as conductivity and magnetism that are crucial for future technologies. The metal-radical approach is especially important for the lanthanide ions exhibiting deeply buried 4f-orbitals. The radicals must possess a high spin density on the donor atoms to promote strong coupling. Combining diamagnetic 89 Y ( I = 1/2) with organic radicals allows for invaluable insight into the electronic structure and spin-density distribution. This approach is hitherto underutilized, possibly owing to the challenging synthesis and purification of such molecules. Herein, evidence of an unprecedented bisbenzimidazole radical anion (Bbim 3− ˙) along with its metalation in the form of an yttrium complex, [K(crypt-222)][(Cp* 2 Y) 2 (μ-Bbim˙)] is provided. Access of Bbim 3− ˙ was feasible through double-coordination to the Lewis acidic metal ion and subsequent one-electron reduction, which is remarkable as Bbim 2− was explicitly stated to be redox-inactive in closed-shell complexes. Two molecules containing Bbim 2− (1) and Bbim 3− ˙ (2), respectively, were thoroughly investigated by X-ray crystallography, NMR and UV/Vis spectroscopy. Electrochemical studies unfolded a quasi-reversible feature and emphasize the role of the metal centre for the Bbim redox-activity as neither the free ligand nor the Bbim 2− complex led to analogous CV results. Excitingly, a strong delocalization of the electron density through the Bbim 3− ˙ ligand was revealed via temperature-dependent EPR spectroscopy and confirmed through DFT calculations and magnetometry, rendering Bbim 3− ˙ an ideal candidate for single-molecule magnet design. 

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5. Difluorination at Boron Leads to the First Electrophilic Ligated Boryl Radical (NHC-BF ₂ ^. )

   https://doi.org/10.1002/anie.201806476  

   Subervie, Daniel; Graff, Bernadette; Nerkar, Swapnil; Curran, Dennis P.; Lalevée, Jacques; Lacôte, Emmanuel (August 2018, Angewandte Chemie International Edition)