title: Isostructural bis-1,2,3-thiaselenazolyl dimers.
abstract: Reduction of the N-methylated bis-1,2,3-thiaselenazolylium salts [2a,b,c][OTf] (with R(1) = Me and R(2) = H (2a), F (2b), Me (2c)) affords the corresponding bis-1,2,3-thiaselenazolyl radicals 2a,b,c. The radicals crystallize as centrosymmetric Se-Se sigma-bonded dimers [2a,b,c](2), in which an intramolecular Se-S bond of the radical is cleaved and replaced by an intermolecular Se-Se bond. The crystal structures of the three dimers are isomorphous, all belonging to the monoclinic space group P2(1)/c, and consist of interpenetrating, cross-braced, slipped pi-stack arrays laced together by numerous short intermolecular Se-N' and Se-S' contacts. In the solid state the dimers are diamagnetic, and behave as small band gap semiconductors with a room temperature conductivity sigma(RT) near 10(-6) S cm(-1). Application of pressure leads to a dramatic increase in conductivity for all three compounds. At 5 GPa the value of sigma(RT) ranges from near 10(-1) S cm(-1) for [2c](2) to 1 S cm(-1) for [2b](2) and 10(1) S cm(-1) for [2a](2). Comparison of the three crystal structures suggests that the compressibility of [2a](2), and hence the response of its conductivity to pressure, is superior to that of [2b,c](2).
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Alicea A
authors.initials: AA
authors.lastname: Leitch
authors.forename: Xueyang
authors.initials: X
authors.lastname: Yu
authors.forename: Craig M
authors.initials: CM
authors.lastname: Robertson
authors.forename: Richard A
authors.initials: RA
authors.lastname: Secco
authors.forename: John S
authors.initials: JS
authors.lastname: Tse
authors.forename: Richard T
authors.initials: RT
authors.lastname: Oakley