The Heterocyclic Diradical Benzo-1,2:4,5-bis(1,3,2-dithiazolyl). Electronic, Molecular and Solid State Structure

Abstract

The preparation and purification of the heterocyclic diradical benzo-1,2:4,5-bis(1,3,2-dithiazolyl) (BBDTA) is described. Crystals of BBDTA, grown by fractional sublimation at 120-180°C/10 -3 Torr, are monoclinic, space group P2 1 /c, with a ) 4.144(2), b ) 9.0344(13), and c ) 10.7424(16) Å, ) 91.11(3)°, and Z ) 2. The crystal structure consists of discrete, unassociated molecules of BBDTA. The molecules form slipped stacks along the x direction, with the mean molecular plane making an angle of 32.4°to the x axis. The interplanar separation between consecutive molecules along the stacking direction is 3.49 Å. The ESR spectrum of BBDTA is solvent dependent, displaying signals attributable to partially associated materials (not exchange coupled) and to free diradical (exchange coupled). Ab initio molecular orbital calculations suggest a small (ca. 0.5 kcal/mol) separation between the triplet and singlet diradical states. Cyclic voltammetry on BBDTA and the related benzo-1,3,2-dithiazolyl BDTA, coupled with gas phase photoelectron studies on BDTA, establish that both compounds are strong electron donors. Magnetic susceptibility measurements show that BBDTA is essentially diamagnetic up to room temperature; variable temperature single-crystal conductivity measurements provide a band gap of 0.22 eV. The transport properties are discussed in the light of extended Hückel band structure calculations, which suggest a highly three-dimensional electronic structure for bulk BBDTA in the solid state.

Interactive Radical Dimers in Photoconductive Organic Thin Films

“…Despite the presence of unpaired electrons as potential charge carriers, organic radicals always exhibit semiconductive behavior that arises from effects such as electron-electron correlations or electron-lattice interactions. [2][3][4][5][6][7][8][9] If such paramagnetic semiconductive materials are incorporated into organic electronic devices, it is expected that they will work under a very different operating principle.…”

New synthetic pathways into dithiazolyl radicals: Preparation and characterisation of 3′-methyl-benzo-1,3,2-dithiazolyl, M’BDTA

“…Birch reduction with Na/l.NH 3 which may not always support chemically sensitive functional groups. Alternatively more complex multi-step pathways are required [10]. Moreover the 1,2-dithiols are often particularly malodorous, low melting point solids or liquids with limited chemical stability, often decomposing to the corresponding disulfide bridged dimer over time when exposed to atmospheric oxygen.…”

Reversible Spin Pairing in Crystalline Organic Radicals

“…[28][29][30][31][32][33][34][35][36] Several other DTA derivatives exhibit spin-Peierls like behaviour. 37,38 Amongst these spin-transition dithiazolyls, TTTA has been most comprehensively studied and is presented as a case study in the next section.…”

“…Whilst neutral organic molecules tend to favour herringbone motifs, 46 the inclusion of electronegative atoms in the molecular backbone of DTAs appears to favour the layer-like motifs desirable for spin-transition properties. [31][32][33][34][35] …”