The Radical Ions of Dipleiadiene (Dicyclohepta[de,ij]naphthalene) and Its 12b,12c-Homo Derivative. An ESR and ENDOR study

The radical anions and the radical cations of dipleiadiene (dicyclohepta[de,ij]naphthalene; 1 ) and its 12b, 12c-homo derivative 2 were characterized by ESR and ENDOR spectroscopy. Their singly occupied orbitals are related to the degenerate nonbonding MOs of a 16-membered π-perimeter. The π-spin distribution over the perimeter is similar in the radical cations 1 ^.+ and 2 ^.+, and an analogous statement holds for the radical anions 1 ^.? and 2 ^.?. However, deviations of the π-system from planarity lead to a decrease in the absolute values of the negative coupling constants of the perimeter protons in 2 ^.+ and 2 ^.? relative to those in 1 ^.+ and 1 ^.?. The hyperfine data for the perimeter protons in the radical ions correlate with the changes in ¹³C chemical shifts on passing from the neutral compounds to the corresponding diions. It is concluded from the coupling constants of the CH₂ protons in the radical ions of 2 that the cation 2 ^.+ exists in the methano-bridged form ( A ) of the neutral 2 (and, presumably, also of the dication 2 ²⁺), whereas the anion 2 ^.? adopts the bisnorcaradiene form ( B ) of the dianion 2 ^2?.     

Single‐Electron Self‐Exchange between Cage Hydrocarbons and Their Radical Cations in the Gas Phase

We show that the radical cations of adamantane (C₁₀H₁₆^.+, 1 H^.+) and perdeuteroadamantane (C₁₀D₁₆^.+, 1 D^.+) are stable species in the gas phase. The radical cation of adamantylideneadamantane (C₂₀H₂₈^.+, 2 H^.+) is also stable (as in solution). By using the natural ¹³C abundances of the ions, we determine the rate constants for the reversible isergonic single‐electron transfer (SET) processes involving the dyads 1 H^.+/ 1 H, 1 D^.+/ 1 D and 2 H^.+/ 2 H. Rate constants for the reaction 1 H^.++ 1 D? 1 H+ 1 D^.+ are also determined and Marcus’ cross‐term equation is shown to hold in this case. The rate constants for the isergonic processes are extremely high, practically collision‐controlled. Ab initio computations of the electronic coupling (H_DA) and the reorganization energy (λ) allow rationalization of the mechanism of the process and give insights into the possible role of intermediate complexes in the reaction mechanism.     

The First Step of the Oxidation of Elemental Sulfur: Crystal Structure of the Homopolyatomic Sulfur Radical Cation [S8].+

The oxidation of elemental sulfur in superacidic solutions and melts is one of the oldest topics in inorganic main group chemistry. Thus far, only three homopolyatomic sulfur cations ([S₄]²⁺, [S₈]²⁺, and [S₁₉]²⁺) have been characterized crystallographically although ESR investigations have given evidence for the presence of at least two additional homopolyatomic sulfur radical cations in solution. Herein, the crystal structure of the hitherto unknown homopolyatomic sulfur radical cation [S₈]^.+ is presented. The radical cation [S₈]^.+ represents the first step of the oxidation of the S₈ molecule present in elemental sulfur. It has a structure similar to the known structure of [S₈]²⁺, but the transannular sulfur⋅⋅⋅sulfur contact is significantly elongated. Quantum-chemical calculations help in understanding its structure and support its presence in solution as a stable compound. The existence of [S₈]^.+ is also in accord with previous ESR investigations.     

Spectroelectrochemical and spectrophotochemical properties of N-tetradecyl-N '-ethyl-viologen: Micellar effects

The results of Spectroelectrochemical studies in homogenous solutions have shown that below the cmc value the cation radical of N-tetradecyl-N '-ethyl viologen (TDEV) dimerizes. The TDEV and tetradecyltriethyl-ammonium bromide (TDEA) micelles were found to stabilize the cation radical TDEV^.+ and increase the rate constant for the reaction TDEV+TDEV²⁺ = TDEV^.+ as compared with the results obtained at concentrations below cmc.Based on the spectrophotochemical measurements for TDEV it was found that the quantum yield (Φ) of photoreduction in micellar evironment of TDEA was twice as large as Φ for reactions performed in homogenous solution. Moreover, in micellar solutions photoreduction of TDEV leads to a cation radical of reduced TDEV (TDEV⁺), but in homogenous solution to the dimer of TDEV [TDEV]₂. Therefore, the process of dimerization of TDEV^.+ cation radical is inhibited by micellar catalysis.     

Quadruple Switching of Pleated Foldamers of Tetrathiafulvalene–Bipyridinium Alternating Dynamic Covalent Polymers

Two dynamic covalent polymers P1 and P2 were prepared by alternately linking electron‐rich tetrathiafulvalene (TTF) and electron‐deficient bipyridinium (BIPY²⁺) through hydrazone bonds. In acetonitrile, the polymers were induced by intramolecular donor–acceptor interactions to form pleated foldamers, which unfolded upon oxidation of the TTF units to the radical cation TTF^.+. Reduction of the BIPY²⁺ units to BIPY^.+ led to the formation of another kind of pleated secondary structures, which are stabilized by intramolecular dimerization of the BIPY^.+ units. The diradical dicationic cyclophane cyclobis(paraquat‐p‐phenylene) (CBPQT^2(.+)) could further force the folded structures to unfold by including the BIPY^.+ units of the polymers. Upon oxidation of the BIPY^.+ units of the cyclophane and polymers to BIPY²⁺, the first folded state was regenerated. Switching or conversion between the four conformational states was confirmed by UV/Vis spectroscopic experiments.     

Influence of Ring Annelation on the Mode Selectivity of the Ionized Diazabicycloheptenes and Corresponding Housanes: An ESR and ENDOR Study

The tricyclic azoalkanes, (1α,4α,4aα,7aα)‐4,4a,5,6,7,7a‐hexahydro‐1,4,8,8‐tetramethyl‐1,4‐methano‐1H‐cyclopenta[d]pyridazine ( 1c ), (1α,4α,4aα,6aα)‐4,4a,5,6,6a‐pentahydro‐1,4,7,7‐tetramethyl‐1,4‐methano‐1H‐cyclobuta[d]pyridazine ( 1d ), (1α,4α,4aα,6aα)‐4,4a,6a‐trihydro‐1,4,7,7‐tetramethyl‐1,4‐methano‐1H‐cyclobuta[d]pyridazine ( 1e ), and (1α,4α,4aα,5aα)‐4,4a,5,5a‐tetrahydro‐1,4,6,6‐tetramethyl‐1,4‐methano‐1H‐cyclopropa[d]pyridazine ( 1f ), as well as the corresponding housanes, the 2,3,3,4‐tetramethyl‐substituted tricyclo[3.3.0.0^2,4]octane ( 2c ), tricyclo[3.2.0.0^2,4]heptane ( 2d ), and tricyclo[3.2.0.0^2,4]hept‐6‐ene ( 2e ), were subjected to γ‐irradiation in Freon matrices. The reaction products were identified with the use of ESR and, in part, ENDOR spectroscopy. As expected, the strain on the C‐framework increases on going from the cyclopentane‐annelated azoalkanes and housanes ( 1c and 2c ) to those annelated by cyclobutane ( 1d and 2d ), by cyclobutene ( 1e and 2e ), and by cyclopropane ( 1f ). Accordingly, the products obtained from 1c and 2c in all three Freons used, CFCl₃, CF₃CCl₃, and CF₂ClCFCl₂, were the radical cations 3c ^.+ and 2c ^.+ of 2,3,4,4‐tetramethylbicyclo[3.3.0]oct‐2‐ene and 2,3,3,4‐tetramethylbicyclo[3.3.0]octane‐2,4‐diyl, respectively. In CFCl₃ and CF₃CCl₃ matrices, 1d and 2d yielded analogous products, namely the radical cations 3d ^.+ and 2d ^.+ of 2,3,4,4‐tetramethylbicyclo[3.2.0]hept‐2‐ene and 2,3,3,4‐tetramethylbicyclo[3.2.0]heptane‐2,4‐diyl. The radical cations 3c ^.+ and 3d ^.+ and 2c ^.+ and 2d ^.+ correspond to their non‐annelated counterparts 3a ^.+ and 3b ^.+, and 2a ^.+ and 2b ^.+ generated previously under the same conditions from 2,3‐diazabicyclo[2.2.1]hept‐2‐ene ( 1a ) and bicyclo[2.1.0]pentane ( 2a ), as well as from their 1,4‐dimethyl derivatives ( 1b and 2b ). However, in a CF₂ClCFCl₂ matrix, both 1d and 2d gave the radical cation 4d ^.+ of 2,3,3,4‐tetramethylcyclohepta‐1,4‐diene. Starting from 1e and 2e , the radical cations 4e ^.+ and 4e′ ^.+ of the isomeric 1,2,7,7‐ and 1,6,7,7‐tetramethylcyclohepta‐1,3,5‐trienes appeared as the corresponding products, while 1f was converted into the radical cation 4f ^.+ of 1,5,6,6‐tetramethylcyclohexa‐1,4‐diene which readily lost a proton to yield the corresponding cyclohexadienyl radical 4f ^.. Reaction mechanisms leading to the pertinent radical cations are discussed.     

Formation of the Charge-Localized Dimer Radical Cation of 2-Ethyl-9,10-dimethoxyanthracene in Solution Phase

Although dimer radical ions of aromatic molecules in the liquid-solution phase have been intensely studied, the understanding of charge-localized dimers, in which the extra charge is localized in a single monomer unit instead of being shared between two monomer units, is still elusive. In this study, the formation of a charge-localized dimer radical cation of 2-ethyl-9,10-dimethoxyanthracene (DMA), (DMA)₂^.+ is investigated by transient absorption (TA) and time-resolved resonance Raman (TR³) spectroscopic methods combined with a pulse radiolysis technique. Visible- and near-IR TA signals in highly concentrated DMA solutions supported the formation of non-covalent (DMA)₂^.+ by association of DMA and DMA^.+. TR³ spectra obtained from 30 ns to 300 μs time delays showed that the major bands are quite similar to those of DMA except for small transient bands, even at 30 ns time delay, suggesting that the positive charge of non-covalent (DMA)₂^.+ is localized in a single monomer unit. From DFT calculations for (DMA)₂^.+, our TR³ spectra showed the best agreement with the calculated Raman spectrum of charge-localized edge-to-face T-shaped (DMA)₂^.+, termed DT^.+, although the charge-delocalized asymmetric π-stacked face-to-face (DMA)₂^.+, termed DF3^.+, is the most stable structure of (DMA)₂^.+ according to the energetics from DFT calculations. The calculated potential energy curves for the association between DMA^.+ and DMA showed that DT^.+ is likely to be efficiently formed and contribute significantly to the TR³ spectra as a result of the permanent charge-induced Coulombic interactions and a dynamic equilibrium between charge localized and delocalized structures.     

Synthesis,Crystal Structure,and Physical Property of Sterically Unprotected Thiophene/Phenylene Co‐Oligomer Radical Cations: A Conductive π–π Bonded Supermolecular meso‐Helix

Sterically unprotected thiophene/phenylene co‐oligomer radical cation salts BPnT^.+[Al(OR_F)₄]^? (OR_F=OC(CF₃)₃, n=1–3) have been successfully synthesized. These newly synthesized salts have been characterized by UV/Vis‐NIR absorption and EPR spectroscopy, and single‐crystal X‐ray diffraction analysis. Their conductivity increases with chain length. The formed meso‐helical stacking by cross‐overlapping radical cations of BP2T^.+ is distinct from previously reported face‐to‐face overlaps of sterically protected (co‐)oligomer radical cations.     

para‐Phenylene‐Bridged Spirobi(triarylamine) Dimer with Four Perpendicularly Linked Redox‐Active π Systems

para‐Phenylene‐bridged spirobi(triarylamine) dimer 2 , in which π conjugation through four redox‐active triarylamine subunits is partially segregated by the unique perpendicular conformation, was prepared and characterized by structural, electrochemical, and spectroscopic methods. Quantum chemical calculations (DFT and CASSCF) predicted that the frontier molecular orbitals of 2 are virtually fourfold degenerate, so that the oxidized states of 2 can give intriguing electronic and magnetic properties. In fact, the continuous‐wave ESR spectroscopy of radical cation 2 ^.+ showed that the unpaired electron was trapped in the inner two redox‐active dianisylamine subunits, and moreover was fully delocalized over them. Magnetic susceptibility measurements and pulsed ESR spectroscopy of the isolated salts of 2 , which can be prepared by treatment with SbCl₅, revealed that the generated tetracation 2 ⁴⁺ decomposed mainly into a mixture of 1) a decomposed tetra(radical cation) consisting of a tri(radical cation) moiety and a trianisylamine radical cation moiety (≈75 %) and 2) a diamagnetic quinoid dication in a tetraanisyl‐p‐phenylendiamine moiety and two trianisylamine radical cation moieties (≈25 %). Furthermore, the spin‐quartet state of the tri(radical cation) moiety in the decomposed tetra(radical cation) was found to be in the ground state lying 30 cal mol^?1 below the competing spin‐doublet state.     

Studies on a Vinyl Ruthenium‐Modified Squaraine Dye: Multiple Visible/Near‐Infrared Absorbance Switching through Dye‐ and Substituent‐Based Redox Processes

The bis(vinyl ruthenium)‐modified squaraine dye 1 was synthesized by treatment of [RuHCl(CO)(PiPr₃)₂] with bis(ethynyl)‐substituted squaraine 8 . Spectroscopic and electrochemical measurements on 1 and its organic precursors 6 – 8 were performed to study the effect of the vinyl ruthenium “substituents,” particularly with respect to (poly)electrochromism. Attachment of the vinyl ruthenium moieties endows metal–organic squaraine 1 with two additional oxidation waves and lowers the first two oxidation potentials by approximately 300 mV with respect to its organic precursors. Squaraines 6 , 7 , 8 , and 1 strongly absorb at 648, 663, 656, or 709 nm. Although organic dyes 6 , 7 , and 8 fluoresce, no room‐temperature emission is observed for 1 . The radical cations and anions of 6 , 7 , 8 , and 1 as well as the doubly oxidized dications have been studied by IR and UV/Vis/NIR spectroelectrochemistry, and the ?/0/+/2+ redox sequences were found to be reversible in each case. Our results indicate that the 1^2?/?/0/+/2+ redox system constitutes a polyelectrochromic switch in which absorption in the visible or the near‐infrared range is reversibly turned off or shifted deep into the NIR. They also show that radical cation 1^.+ is an intrinsically delocalized system with only little contribution from the outer vinyl ruthenium tags to the oxidation process. Dication 1²⁺ constitutes a class‐II mixed‐valent system with two electronically different vinyl ruthenium moieties and has an open‐shell singlet electronic ground‐state structure. ESR and NMR spectra of chemically prepared 1^.+ and 1²⁺ corroborate these results. It has also emerged that reduction involves an orbital that is strongly delocalized across the entire squaraine π system and strongly affects the peripheral vinyl ruthenium sites.     

Mechanistic aspects of the bromination of 10-substituted phenothiazines

The addition of 1 and 2 molar equivalents of bromine to a series of 10-alkylphenothiazines, 1a-d (methyl, ethyl, n-propyl, and isopropyl, respectively), yields the corresponding 3-bromo- and 3,7-dibromo-10-alkylphenothiazines ( 11a-d and 12a-d , respectively). Evidence which supports the typical clectrophilic aromatic substitution mechanism is presented. Radical cations ( 12a-d^.+ ) arc produced when 12a-d are treated with 1 or 2 molar equivalents of bromine. Upon boiling in acetic acid these radical cations are converted predominantly to 1,3,7,9-lelrabromophenothiazine ( 5 ) and the parent 3,7-dibromo-10-alkylphenothiazine ( 12a-d ) with the evolution of hydrogen bromide. The 10-methyl radical ( 12a ) gives, in addition, 1,3,7-tribromo-10-methylphenothiazine ( 15 ). A mechanism if proposed for these reactions in which initial dealkylution of 12b-d^.+ to 3.7-dibromophenothiazine radical cation ( 13 ) occurs followed by reduction of 13^.+ by bromide ion to parent 3,7-dibromophenothiazine ( 13 ). Subsequent bromination of 13 by molecular bromine produced in the previous redox reaction yields 1,3,7-tribromo-( 14 ) and 1,3,7,9-tetra-bromo-( 5 ) phenothiazines. The small size of the methyl group allows 12a to be brominated at the 1-position prior to dealkylation. In addition to undergoing bromination at the 3- and 7-position, 10-isopropylphenothiazine ( 1d ) is oxidized to the radical cation 12e^.+ when treated with bromine. 10-Benzylphenothiazine ( 1e ), however, undergoes oxidation to radical cation 1e^.+ exclusively. This radical cation debenzylates readily at room temperature and is converted finally into phenothiazine.     

Kinetics and mechanism of formation and decay of 2,2′-azinobis-(3-ethylbenzothiazole-6-sulphonate) radical cation in aqueous solution by inorganic peroxides

The kinetics of oxidation of 2,2′-azinobis-(3-ethylbenzothiazole-6-sulphonate) (ABTS) by the inorganic peroxides, peroxomonosulphate, peroxodisulphate, peroxodiphosphate, and hydrogen peroxide were investigated in aqueous solution. The kinetics of formation of the radical cation, ABTS^.+, on one-electron abstraction by these peroxides and the further reaction of ABTS^.+ with higher concentrations of these peroxides at longer time scale were studied by following the growth and decay of the radical cation, ABTS^.+ at 417 nm. The rate of formation of ABTS^.+ was found to obey a total second-order, first-order each in [ABTS] and [peroxide], except for H₂O₂, which reacted through Michaelis-Menten kinetics. All the peroxides investigated were found to react with ABTS^.+; however peroxodisulphate alone oxidized ABTS^.+ to the dication (ABTS⁺⁺), the other peroxides reacted via ionic mechanism, probably forming sulphoxide and sulphone as products. The kinetics of decay of the radical cation, ABTS^.+, was also found to follow a total second-order, first-order each in [ABTS^.+] and [peroxide], except peroxodiphosphate the reaction of which obeyed Michaelis-Menten kinetics. The effect of pH and temperature were also investigated in all the systems and the kinetic and thermodynamic parameters were evaluated and discussed with suitable reaction mechanisms.     

Low-Temperature Isolation of a Labile Silylated Hydrazinium-yl Radical Cation, [(Me3Si)2N−N(H)SiMe3].+

The oxidation of silylated hydrazine, (Me₃Si)₂N−N(H)SiMe₃, with silver salts led to the formation of a highly labile hydrazinium-yl radical cation, [(Me₃Si)₂N−N(H)SiMe₃]^.+, at very low temperatures (decomposition > −40 °C). EPR, NMR, DFT and Raman studies revealed the formation of a nitrogen-centered radical cation along the N−N unit of the hydrazine. In the presence of the weakly coordinating anion [Al{OCH(CF₃)₂}₄]⁻, crystallization and structural characterization in the solid state were achieved. The hydrazinium-yl radical cation has a significantly shortened N−N bond and a nearly planar N₂Si₃ framework, in contrast to the starting material. According to DFT calculations, the shortened N−N bond has a total bond order of 1.5 with a π-bond order of 0.5. The π bond can be regarded as a three-π-electron, two-center bond.     

C4 Cumulene and the Corresponding Air‐Stable Radical Cation and Dication

A neutral C₄ cumulene 1 that includes a cyclic alkyl(amino) carbene (cAAC), its air‐stable radical cation 1 ^.+, and dication 1 ²⁺ have been synthesized. The redox property of 1 ^.+ was studied by cyclic voltammetry. EPR and theoretical calculations show that the unpaired electron in 1 ^.+ is mainly delocalized over the central C₄ backbone. The commercially available CBr₄ is utilized as a source of dicarbon in the cumulene synthesis.     

SET and HAT/PCET acid-mediated oxidation processes in helical shaped fused bis-phenothiazines

Helical shaped fused bis-phenothiazines 1 – 9 have been prepared and their red-ox behaviour quantitatively studied. Helicene radical cations (Hel^.+) can be obtained either by UV-irradiation in the presence of PhCl or by chemical oxidation. The latter process is extremely sensitive to the presence of acids in the medium with molecular oxygen becoming a good single electron transfer (SET) oxidant. The reaction of hydroxy substituted helicenes 5 – 9 with peroxyl radicals (ROO^.) occurs with a ‘classical’ HAT process giving HelO^. radicals with kinetics depending upon the substitution pattern of the aromatic rings. In the presence of acetic acid, a fast medium-promoted proton-coupled electron transfer (PCET) process takes place with formation of HelO^. radicals possibly also via a helicene radical cation intermediate. Remarkably, also helicenes 1 – 4 , lacking phenoxyl groups, in the presence of acetic acid react with peroxyl radicals through a medium-promoted PCET mechanism with formation of the radical cations Hel^.+. Along with the synthesis, EPR studies of radicals and radical cations, BDE of Hel-OH group (BDE_OH), and kinetic constants (k_inh) of the reactions with ROO^. species of helicenes 1 – 9 have been measured and calculated to afford a complete rationalization of the redox behaviour of these appealing chiral compounds.     

ESR and quantum chemical studies of the structures and thermal transformations of the radical cations of vinylcyclopropane in irradiated frozen Freon matrices. Simulation of radical processes in solids

Thermal transformations of vinylcyclopropane radical cations (VCP^.+) in X-ray-irradiated frozen Freon matrices (CFCl₂CF₂Cl and CFCl₃) were studied by ESR; radical processes involving VCP^.+ in solid VCP were simulated.Gauche- andanti-VCP ^.+ were found to be the primary radical cations, however, the former, unlike the latter, is stable only under gas-phase conditions. The thermodynamic equilibrium betweenanti-VCP^.+ and its less stable distonic form,dist(90,0)-C ₅H₈ ^.+, is established in frozen Freon matrices and the VCP host matrix; the structure of dist(90,0)****-C ₅H₈ ^.+ is stabilized by a molecule ofanti-VCP. In CFC₃, along with dist(90,0)-C₅H₈ ^.+,-dimeric resonance [anti-VCP]₂ ^.+ complex was detected. A general scheme of the transformations of VCP^.+ in the solid phase has been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 11–21, January, 1994.     

Effect of Annulation Mode of Twistarene on the Physical Property and Self-Assembly Behavior of Functionalized Curved Aromatic Molecules

Four novel curved polycyclic aromatic hydrocarbons 3 a , 5 , 8 , 15 a have been synthesized and characterized, where molecules 3 a and 15 a bear [5]carbohelicene units. X-ray single crystal analyses indicate that compound 3 a shows offset packing arrangements of (P₅)- and (M₅)-isomers, and 15 a has a symmetrical plane and looks like a butterfly. In comparison, 8 exhibits a slightly curved structure, in which the significant convex-to-convex π-overlap with the shortest distance of 3.42 Å occurs. In addition, the effect of annulation mode of twistarenes on the physical properties, self-assembly behaviors, and switchable photoconductivity of the as-prepared curved aromatic compounds were further examined in a comparative manner.     

2,2′‐Bipyridinium(1+) bromide monohydrate

In the crystal structure of 2,2′‐bipyridinium(1+) bromide monohydrate, C₁₀H₉N₂⁺·Br⁻·H₂O, the cation has a cisoid conformation with an intramolecular N—H⋯N hydrogen bond. The cation also forms an N—H⋯O hydrogen bond to an adjacent water mol­ecule, which in turn forms O—H⋯Br⁻ hydrogen bonds to adjacent Br⁻ anions. In this way, a chain is formed extending along the b axis. Additional interactions (C—H⋯Br⁻ and π–π) serve to stabilize the structure further.     

Elusive Antimony‐Centered Radical Cations: Isolation,Characterization, Crystal Structures,and Reactivity Studies

One‐electron oxidation of the stibines Aryl₃Sb ( 1 , Aryl=2,6‐ⁱ Pr₂‐4‐OMe‐C₆H₂; 2 , Aryl=2,4,6‐ⁱ Pr₃‐C₆H₂) with AgSbF₆ and NaBAryl^F₄ (Aryl^F=3,5‐(CF₃)₂C₆H₃) afforded the first structurally characterized examples of antimony‐centered radical cations 1 ^.+[BAryl^F₄]⁻ and 2 ^.+[BAryl^F₄]⁻. Their molecular and electronic structures were investigated by single‐crystal X‐ray diffraction, electron paramagnetic resonance spectroscopy (EPR) and UV/Vis absorption spectroscopy, in conjunction with theoretical calculations. Moreover, their reactivity was investigated. The reaction of 2 ^.+[BAryl^F₄]⁻ and p ‐benzoquinone afforded a dinuclear antimony dication salt 3 ²⁺[BAryl^F₄]₂⁻, which was characterized by NMR spectroscopy and X‐ray diffraction analysis. The formation of the dication 3 ²⁺ further confirms that the isolated stibine radical cations are antimony‐centered.     

Elusive Antimony‐Centered Radical Cations: Isolation,Characterization, Crystal Structures,and Reactivity Studies

One‐electron oxidation of the stibines Aryl₃Sb ( 1 , Aryl=2,6‐ⁱ Pr₂‐4‐OMe‐C₆H₂; 2 , Aryl=2,4,6‐ⁱ Pr₃‐C₆H₂) with AgSbF₆ and NaBAryl^F₄ (Aryl^F=3,5‐(CF₃)₂C₆H₃) afforded the first structurally characterized examples of antimony‐centered radical cations 1 ^.+[BAryl^F₄]⁻ and 2 ^.+[BAryl^F₄]⁻. Their molecular and electronic structures were investigated by single‐crystal X‐ray diffraction, electron paramagnetic resonance spectroscopy (EPR) and UV/Vis absorption spectroscopy, in conjunction with theoretical calculations. Moreover, their reactivity was investigated. The reaction of 2 ^.+[BAryl^F₄]⁻ and p ‐benzoquinone afforded a dinuclear antimony dication salt 3 ²⁺[BAryl^F₄]₂⁻, which was characterized by NMR spectroscopy and X‐ray diffraction analysis. The formation of the dication 3 ²⁺ further confirms that the isolated stibine radical cations are antimony‐centered.