1,2,3,5‐Dithiadiazolyl Radicals

Nascimento, Mitchell A.; Rawson, Jeremy M.

doi:10.1002/9781119951438.eibc2640

Cited by 6 publications

(11 citation statements)

References 85 publications

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“…In this context we targeted the 9′-anthracenyl radical, 3 , which has the potential to combine the fluorescent properties of the anthracenyl group with the paramagnetic DTDA radical. A preliminary search of the CSD for CN 2 fragments bound to the 9′-anthracenyl group revealed an average twist angle of 52° between the CN 2 plane and the anthracenyl group, which augered well for the common cis -oid dimerization process to be suppressed in 3 . While p -NCC 6 F 4 CNSSN and 2,4,6-(F 3 C) 3 C 6 H 2 CNSSN both retain their paramagnetism in the solid state and both exhibit two polymorphs, , we have found 3 not only retains its paramagnetism in the solid state but also exhibits a remarkably rich polymorphism.…”

Section: Introductionmentioning

confidence: 99%

Structural, Magnetic, and Optical Studies of the Polymorphic 9′-Anthracenyl Dithiadiazolyl Radical

et al. 2019

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The fluorescent 9′-anthracenyl-functionalized dithiadiazolyl radical (3) exhibits four structurally determined crystalline phases, all of which are monomeric in the solid-state. Polymorph 3α (monoclinic P21/c, Z' = 2) is isolated when the radical is condensed onto a cold substrate (enthalpically favored polymorph) whereas 3β (orthorhombic P212121, Z' = 3) is collected on a warm substrate (entropically favored polymorph). The α and β polymorphs exhibit chemically distinct structures with 3α exhibiting face-to-face π−π interactions between anthracenyl groups while 3β exhibits edge-to-face π−π interactions. 3α undergoes an irreversible conversion to 3β on warming to 120 o C (393 K). The β-phase undergoes a series of reversible solid-state transformations on cooling; below 300 K a phase transition occurs to form 3γ (monoclinic P21/c, Z' = 1) and on further cooling below 165 K a further transition is observed to 3δ (monoclinic P21/n, Z' = 2). Both 3β  3γ and 3γ  3δ transitions are reversible (single-crystal X-ray diffraction) and the 3γ  3δ process exhibits thermal hysteresis with a clear feature observed by heat capacity measurements. Heating 3β above 160 o C generates a fifth polymorph (3ε) which is distinct from 3α -3δ based on PXRD data. The magnetic behavior of both 3α and the 3β/3γ/3δ system reflect an S = ½ paramagnet with weak antiferromagnetic coupling. The reversible 3δ ↔ 3γ phase transition exhibits thermal hysteresis of 20 K. Below 50 K the value of χmT for 3δ approaches 0 emu•K•mol -1 consistent with formation of a gapped state with an S = 0 ground state configuration. In solution both paramagnetic 3 and diamagnetic [3][GaCl4] exhibit similar absorption and emission profiles reflecting similar absorption and emission mechanisms for paramagnetic and diamagnetic forms. Both emit in the deep-blue region of the visible spectrum (λem ~ 440 nm) upon excitation at 255 nm with quantum yields of 4% (3) and 30% ([3][GaCl4]) affording a switching ratio [ΦF(3 + )/ΦF(3)] of 7.5 in quantum efficiency with oxidation state. Solid-state films of both 3 and [3][GaCl4] exhibit emission bands at longer wavelength (490 nm) attributed to excimer emission.

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Section: Introductionmentioning

confidence: 99%

Structural, Magnetic, and Optical Studies of the Polymorphic 9′-Anthracenyl Dithiadiazolyl Radical

et al. 2019

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“…Stable dithiazolyl ( DTA ) radicals occur in three major classes, , as outlined in Figure . In particular, 1,2,3,5- DTA (or dithiadiazolyl) derivatives, which generally show a strong propensity for dimerization, , provided both an organic radical with the highest ordering temperature and interesting cases of magnetic bistability; − that is, 4-cyanotetrafluorophenyl derivative is a weak ferromagnet (canted antiferromagnet) with an ordering temperature of 36 K. ,,− At high pressure, this material reaches an ordering temperature of 70 K but with the trade-off of decreased spontaneous magnetization (decreased canting) …”

Section: Persistent and Stable Monoradicals As Spin Centersmentioning

confidence: 99%

From Stable Radicals to Thermally Robust High-Spin Diradicals and Triradicals

Shu,

Yang,

Rajca

2023

Chem. Rev.

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Stable radicals and thermally robust high-spin di-and triradicals have emerged as important organic materials due to their promising applications in diverse fields. New fundamental properties, such as SOMO/HOMO inversion of orbital energies, are explored for the design of new stable radicals, including highly luminescent ones with good photostability. A relation with the singlet−triplet energy gap in the corresponding diradicals is proposed. Thermally robust high-spin di-and triradicals, with energy gaps that are comparable to or greater than a thermal energy at room temperature, are more challenging to synthesize but more rewarding. We summarize a number of high-spin di-and triradicals, based on nitronyl nitroxides that provide a relation between the experimental pairwise exchange coupling constant J/k in the high-spin species vs experimental hyperfine coupling constants in the corresponding monoradicals. This relation allows us to identify outliers, which may correspond to radicals where J/k is not measured with sufficient accuracy. Double helical high-spin diradicals, in which spin density is delocalized over the chiral π-system, have been barely explored, with the sole example of such high-spin diradical possessing alternant π-system with Kekuléresonance form. Finally, we discuss a high-spin diradical with electrical conductivity and derivatives of triangulene diradicals.

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“…A structural motif common to this family of radicals is the formation of a π*···π* dimer multicenter bonding interaction (Figure ), which has often been described as a “pancake bond” and reviewed several times in the recent literature. − This pancake bonding comprises a significant covalent contribution with a solution dimerization enthalpy − of ca . −35 kJ mol –1 and estimated dimerization energy in the solid state in the range −10 to −17 kJ mol –1 . ,, The covalent contribution to bonding is manifested in intradimer S···S contacts in the range 2.9–3.1 Å, which is considerably less than the sum of the van der Waals radii (3.6 Å) and strong orientation dependence of the radicals (Figure ) so as to optimize overlap between singly occupied molecular orbitals (SOMOs). − These pancake dimers are essentially diamagnetic in the solid-state, consistent with quenching of the radical paramagnetism. In addition to this multicenter bonding interaction, previous studies have identified a strong tendency for self-assembly through non-covalent interactions between DTDA heterocycles reflected in a number of repeating structural motifs, assigned as SN-I to SN-IV (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Assessment of Computational Methods for Calculating Accurate Non-covalent Interaction Energies in 1,2,3,5-Dithiadiazolyl Radicals

Nikoo

Rawson

2021

Crystal Growth & Design

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The strength of non-covalent intermolecular interactions between dithiadiazolyl (DTDA) radicals XCNSSN (X = F, Cl, Br, CN) were benchmarked using a high-level post-Hartree−Fock ab initio CCSD(T) theory with a complete basis set and corrected with a counterpoise (CP) correction for basis-set superposition error (BSSE). A range of density functional theory (DFT) functionals and basis sets were then screened to identify appropriate DFT methods which would reflect the benchmark data. These identified that minimal basis sets tended to overestimate the interaction energies, whereas inclusion of additional diffuse and polarization functions led to underestimation of these energies. The application of a CP correction for BSSE generally led to inferior performances in relation to uncorrected data for DFT calculations. The relative strengths of the intermolecular interactions were implemented to rationalize the trends in packing within the series XCNSSN (X = F, Cl, Br, CN). The nature of these interactions was also probed through an Atoms in Molecules approach which reveals intermolecular bond critical points for the different types of interactions, which are all diagnostic of non-covalent interactions between DTDA radicals. These are compared with previous experimental charge-density studies on related DTDA radicals. The best-performing DFT methods were then applied to the αand β-polymorphs of the larger radical p-NCC 6 F 4 CNSSN which was too large for benchmark studies. These confirmed the small energetic differences between α and β phases with the top five best-performing methods and functionals correctly reflecting the relative phase stabilities.

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1,2,3,5‐Dithiadiazolyl Radicals

Cited by 6 publications

References 85 publications

Structural, Magnetic, and Optical Studies of the Polymorphic 9′-Anthracenyl Dithiadiazolyl Radical

Structural, Magnetic, and Optical Studies of the Polymorphic 9′-Anthracenyl Dithiadiazolyl Radical

From Stable Radicals to Thermally Robust High-Spin Diradicals and Triradicals

Assessment of Computational Methods for Calculating Accurate Non-covalent Interaction Energies in 1,2,3,5-Dithiadiazolyl Radicals

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