title: Pressure enhanced conductivity in bis-1,2,3-thiaselenazolyl dimers.
abstract: A synthetic sequence to salts of N-alkylated pyridine-bridged 1,2,3-thiaselenazolo-1,2,3-thiaselenazolylium cations [2]+ (R1 = Me, Et; R2 = H) is described. The corresponding radicals 2 (R1 = Me, Et; R2 = H) can be generated from the cations by chemical or electrochemical reduction. Crystals of the two radicals are isostructural and consist of interpenetrating pi-stacked arrays of closed-shell Se-Se sigma-bonded dimers [2]2 laced together with numerous short intermolecular Se- - -Se, Se- - -S, and Se- - -N contacts. Variable-temperature magnetic, conductivity, and near-infrared optical measurements indicate that the bulk materials behave as small band gap semiconductors with room-temperature conductivities sigma(RT) near 10(-6) S cm(-1) and thermal activation energies Ea of 0.32 eV (R1 = Me) and 0.36 eV (R1 = Et). LMTO band structure calculations on both compounds are consistent with this interpretation. The application of external pressure leads to dramatic increases in conductivity; at 4 GPa sigma(RT) reaches a value near 10(-1) S cm(-1) for R1 = Me and 10(-2) S/cm for R1 = Et. The conductivity remains activated for both compounds, but for R1 = Me the activation energy Ea is reduced to near 0.03 eV at 5 GPa, suggestive of a weakly metallic state.
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Leanne
authors.initials: L
authors.lastname: Beer
authors.forename: Jaclyn L
authors.initials: JL
authors.lastname: Brusso
authors.forename: Robert C
authors.initials: RC
authors.lastname: Haddon
authors.forename: Mikhail E
authors.initials: ME
authors.lastname: Itkis
authors.forename: Holger
authors.initials: H
authors.lastname: Kleinke
authors.forename: Alicea A
authors.initials: AA
authors.lastname: Leitch
authors.forename: Richard T
authors.initials: RT
authors.lastname: Oakley
authors.forename: Robert W
authors.initials: RW
authors.lastname: Reed
authors.forename: John F
authors.initials: JF
authors.lastname: Richardson
authors.forename: Richard A
authors.initials: RA
authors.lastname: Secco
authors.forename: Xueyang
authors.initials: X
authors.lastname: Yu