Yassine Beldjoudi

Preparation and crystal structures of the isomeric series 4-tolyl-1,2,3,5-dithiadiazolyl, (o-MeC6H4CNSSN)2, (m-MeC6H4CNSSN)2 and (p-MeC6H4CNSSN)2

The radicals (p-MeC6H4CNSSN)2 (1) (m-MeC6H4CNSSN)2 (2) and (o-MeC6H4CNSSN)2 (3) were prepared from the corresponding tolunitriles using conventional synthetic methodologies and were crystallised by vacuum sublimation. All three structures comprise cis-cofacial π*–π* dimers with one dimer in the asymmetric unit for 1 and 2 and four dimers in the asymmetric unit for 3. In both 1 and 2 the crystal packing reveals close S⋯π(aryl) interactions which drive formation of a double herringbone motif, analogous to that observed in the parent radical [PhCNSSN]2. The double herringbone sheets in both 1 and 2 are linked via Sδ+⋯Nδ− contacts. The presence of the methyl group in the ortho-position has a pronounced effect on the solid state structure of 3; the steric demand of the ortho-methyl group generates a substantially larger twist angle between aryl and heterocyclic rings (19.43–28.07° in 3 compared with 5.20–10.91° in 1 and 2). This induces a larger mean intra-dimer separation (mean S⋯S = 3.117(2) A, cf.1 and 2 at 3.0759(9) and 3.078(1) A) and also inhibits formation of S⋯π interactions in 3. Instead the structure of 3 reveals a layered arrangement of dimers with intra-layer Sδ+⋯Nδ− contacts. The lengthening of the intramolecular S⋯S bond in 3 leads to a weakening of the π*–π* dimer and is manifested in the observation of a thermally accessible triplet state (S = 1) at room temperature by EPR spectroscopy. Warming above room temperature leads to a rapid increase in EPR intensity above 320 K associated with melting of 3.

A fluorescent dithiadiazolyl radical: structure and optical properties of phenanthrenyl dithiadiazolyl in solution and polymer composites

The phenanthrene-functionalised dithiadiazolyl radical 2 provides a rare example of a fluorescent radical, exhibiting bright blue fluorescence (410 nm) in solution (MeCN: ΦF = 0.11). The indirect participation of the radical electron in the fluorescence process is supported by (i) TD-DFT studies and (ii) the observation that the diamagnetic salt [2][GaCl4] also exhibits a similar broad emission at 410 nm. The large Stokes shift appears associated with significant molecular relaxation in the excited state, evidenced by the solvent-independent nature of the absorption profile but marked solvent-dependent emission spectrum. Incorporation of 2 into polymer matrices such as PMMA or polystyrene leads to substantial enhancement in air stability with evidence of efficient emission quenching at higher w/w radical : polymer ratios.

Studies on a “Disappearing Polymorph”: Thermal and Magnetic Characterization of α-p-NCC6F4CNSSN•

The α-and β-phases of the thiazyl radical p-NCC6F4CNSSN• (1) can be selectively prepared by careful control of the sublimation conditions, with the α-phase crystallizing preferentially when the substrate temperature is maintained below -10 °C, whereas the β-phase is isolated when the substrate temperature is maintained at or above ambient temperature. Differential scanning calorimatry studies reveal that the α-phase converts to the β-phase upon warming over the range 111-117 °C (ΔH = +4 kJ·mol-1) via a melt-recrystallization process, with the β-phase itself melting at 167-170 °C (ΔHfus = 27 kJ·mol-1). IR and Raman spectroscopy can be used to clearly discriminate between 1α and 1β. The α-phase shows a broad maximum in the magnetic susceptibility around 8 K that, coupled with a broad maximum in the heat capacity, is indicative of short-range order. Some field dependence of the susceptibility below 3 K is observed, but the lack of features in the ac susceptibility, M vs H plots, or heat capacity mitigates against long-range order in 1α.

Correction to Route to Benzo- and Pyrido-Fused 1,2,4-Triazinyl Radicals via N′-(Het)aryl-N′-[2-nitro(het)aryl]hydrazides

As such, Scheme 7 in the original article should now be as follows: Furthermore, the Experimental Section (section 4.7.2) now becomes: 4.7.2. 5-[1,3-Di(pyrid-2-yl)-7-(tri f luoromethyl)-1,4dihydrobenzo[e][1,2,4]triazin-4-yl]-1,3-di(pyrid-2-yl)-7-(trif luoromethyl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (1o). To a stirred solution of 1,3-di(pyrid-2-yl)-7-(trifluoromethyl)-1,4-dihydro1,2,4-benzotriazine (23c) (355 mg, 1.0 mmol) in DCM (10 mL) at ca. 20 °C was added MnO2 (869 mg, 10.0 mmol). After 2 days, the reaction mixture was filtered through Celite and rinsed with additional DCM, and volatiles were removed in vacuo. The residue was chromatographed on basic alumina (DCM/t-BuOMe, 1:1) to give the title compound 1o (173 mg, 49%) as black needles. Mp (DSC) onset 218.1 °C, peak max 222.9 °C (from MeCN); Rf 0.49 (Al2O3, DCM); (found C, 60.93; H, 3.07; N, 19.89. C36H21F6N10• requires C, 61.11; H, 2.99; N, 19.79%); λmax(DCM)/nm 236 (log ε 4.56), 267 (4.66), 282 inf (4.63), 328 inf (4.36), 436 (3.78), 510 (3.31); νmax/cm −1 3061w and 3011w (Ar CH), 1585m, 1568w, 1514w, 1466m, 1429s, 1402m, 1375m, 1344s, 1325s, 1290m, 1271s, 1233w, 1190w, 1161s, 1115s, 1088m, 1061m, 1043w, 991w, 947w, 912m, 878m, 822m, 800m, 775m, 743m, 733w; MALDITOF (m/z) 709 (MH + 1, 39%), 708 (MH, 100), 696 (24), 630 (8), 617 (20), 603 (9), 588 (17), 354 (8), 342 (9), 339 (6). The structures of the remaining radicals have been rechecked, and their structures are correct. From a brief initial study, it appears that the higher basicity of the dipyridyl 1o is partly responsible for this unexpected dimerization, and we have been unable to find conditions to oxidize the precursor triazine 23c that do not give the dimeric species 1o. This dimerization is now under study, and we plan to provide a full report on this reaction in the very near future.