John J. Hayward

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.

Syntheses of, and structural studies on, benzo-fused 1,2,4-thiadiazines

The syntheses of nine benzo-fused-1,2,4-thiadizines are reported. The use of microwave synthesis has been shown to afford high yields and short reaction times in several key reaction steps. The molecular geometries of these heterocycles are discussed and their solid state packing motifs reveal a strong tendency for the N–H group to form hydrogen bonded chains.

An unusual single-crystal-to-single-crystal (2 + 2) photocyclisation reaction of a TTF-arylnitrile derivative†

4-([2,2′-Bi(1,3-dithiolylidene)]-4-yl)benzonitrile undergoes a [2 + 2] photocycloaddition reaction upon irradiation with polychromatic light, an unusual single-crystal-to-single-crystal transformation for a TTF derivative. In contrast, the closely related pyridylnitrile derivative adopts a different packing motif and is stable to light under the same conditions.

Probing the reactivity of a 2,2′-bipyridyl-3,3′-bis-imine ligand by X-ray crystallography

The reactivity of a Schiff-base bis-imine ligand 3 is probed by X-ray diffraction studies. Its susceptibility to hydrolysis, oxidation and nucleophilic addition reactions is demonstrated by the isolation of the methanol adduct 4 and two diazapene heterocycles 5 and 6. This reactivity is also reflected in the molecular structures of two coordination complexes isolated by the reaction of 3 with M(hfac)2 salts, to afford [Cu(5)(hfac)(tfa)] (8) and [Zn(6)(hfac)2] (9).

CHAPTER 11.1:Stable Chalcogen Radicals

Recent developments in the chemistry of stable chalcogen–nitrogen radicals are discussed, with an emphasis on their electronic structure and bulk physical properties of these radicals and their metal complexes. The strength of radical–radical magnetic interactions gives rise to long‐range magnetic order (ferromagnetism, antiferromagnetism, canted antiferromagnetism) at high temperatures (T <70 K). Chalcogen–nitrogen radicals which span the spectrum from insulating through semiconducting to conducting behaviour are described.