Structure, dielectric relaxation and electrical conductivity of 2,3,7,8-tetramethoxychalcogenanthrene–2,3-dichloro-5,6-dicyano-l,4-benzoquinone 1 : 1 charge-transfer complexes

Abstract

2,3,7,8-Tetramethoxychalcogenanthrenes ( 5,10-chalcogena-cyclo-diveratrylenes, 'Vn2E2', E = S, Se) form isotypical 1 : 1 chargetransfer (CT) complexes with 2,3-dichloro-5,6-dicyano-174-benzoquinone (DDQ). X-ray analysis of Vn, S2 -DDQ shows the compound to have a columnar structure with segregated stacks of donors and acceptors. The donors are virtually planar in accordance with a formulation of [VnzE2] '[DDQ] -. Donor cations and acceptor anions are equidistant in their respective stacks, but in each case they inclined to the stacking axis, nevertheless guaranteeing an optimum overlap of the half-filled frontier orbitals which are of n-type character according to MNDO calculations. Dielectric ac measurements of permittivity E' and loss factor E" clearly reveal two processes, a dielectric one at low temperatures and a conductive one at high temperatures. The dielectric process can be described by the Havriliak-Negami (HN) and the Kohlrausch-Williams-Watts (KWW) model, and the conductive process by a Debye-type plot. Using these methods, the relevant parameters are evaluated. The dc conductivities of polycrystalline samples moulded at lo8 Pa show a temperature dependence in the plots of In t~ us. T -l , which is typical of semiconductors. Two slopes are found; that in the low-temperature region (< 285 K) is explained by an easy-path model (intragrain conductivity with low activation energies), whereas in the high-temperature region conduction across the grain boundaries (with higher activation energies) is becoming predominant. The activation energies for the intrinsic conductivities obtained by the ac and dc measurements are similar. Despite the columnar structure with segregated stacks, due to stoichiometric oxidation states of the components, the absolute values of conductivity are low (ca.

Corannulene Polysulfides: Molecular Bowls with Multiple Arms and Flaps

“…1 Scheme 1 Synthesis of pentakis(1,4-benzodithiino)corannulene (12) An X-ray crystal structure of 12 ( Figure 4) reveals that two molecules of the 'fly-trap' surround one molecule of benzene in this crystal [another is interstitial (not enclathrated)]. The flaps show flexibility by bending various amounts to form a cavity that closely encloses the benzene.…”

“…The organic layer was dried with anhyd MgSO 4 and concentrated to dryness under reduced pressure to give a red oil. Chromatography on silica gel (petroleum ether/Et 2 O = 95/5) gave dodecyldisulfide as a by-product (faster moving on silica gel) and 58 mg (77%) of the decakis(1-dodecylthio)corannulene (10) (12). A suspension of decachlorocorannulene 7 (7, 10 mg, 0.017 mmol), 1,2-benzenedithiol (16 mL, 0.14 mmol) and NaHCO 3 (34 mg, 41 mmol) in 2.0 mL of dry dimethylforamide (DMF) was stirred for 3 h at r.t. under nitrogen.…”

“…The resulting orange suspension was brought to 50°C for 12 h and to 100°C for 4 h. The suspension was then cooled to r.t. and quenched with 10% HCl solution. Extraction with CS 2 and evaporation of the solvent gave 19 mg of an orange residue, which was chromatographed on silica gel (pure CS 2 ) to afford 8 mg (50%) of pentakis(1,4-benzodithiino)corannulene (12). Mp begins to darken at 397 ºC; melts at 403-404 ºC.…”

“…Finally, to build an analog of 3 and 4 that could embrace a molecular guest without having to pay such a high entropic cost, we prepared the 'fly trap' compound, pentakis(1,4-benzodithiino)corannulene (12), by treatment of decachlorocorannulene (7) with the disodium salt of 1,2benzenedithiol (11) in DMEU at room temperature (Scheme 1). 1 Scheme 1 Synthesis of pentakis(1,4-benzodithiino)corannulene (12) An X-ray crystal structure of 12 (Figure 4) reveals that two molecules of the 'fly-trap' surround one molecule of benzene in this crystal [another is interstitial (not enclathrated)]. The flaps show flexibility by bending various amounts to form a cavity that closely encloses the benzene.…”

“…Thianthrenes participating in charge-transfer complexes flatten even further, and a 0° dihedral angle (complete planarity) was twice reported. 12,13 In 12, the distances from the outer edge of the flaps to the SS creases are 3.92-3.93 Å. A flattening of the thianthrene portions of the flaps by just 5° would swing the outer carbon atoms outwards by 0.35 Å, enough to allow much better docking.…”