title: Stacking efficiency of diselenadiazolyl pi-dimers. Consequences for electronic structure and transport properties.
abstract: The preparation and crystal structure of 5-cyanofuran-2-[1,2,3,5-diselenadiazolyl], [RCN(2)Se(2)] (R = 5-cyanofuran), is reported. Crystal data for C(6)H(2)ON(3)Se(2): monoclinic, space group P2(1), a = 7.1121(7), b= 20.541(2), c =20.923(2) A, beta = 99.785(1) degrees, Z = 16. The crystal structure consists of diselenadiazolyl pi-dimer stacks running parallel to the x direction; the asymmetric unit consists of four pi-dimer units. The dimers are aligned into snakelike ribbons along the y direction, with consecutive dimers linked by head-to-tail CN-Se contacts. Each pi-dimer stack is bordered by two out-of-register stacks, but most interstack Se-Se contacts lie outside the van der Waals separation. Along the pi-dimer stacks, the intradimer Se-Se distances range from 3.183(10) to 3.294(1) A, and the interdimer Se-Se distances range from 3.826(1) to 3.945(1) A. Like other pi-dimer stacked diselenadiazolyls, [C(6)H(2)ON(3)Se(2)](2) is diamagnetic over the temperature range 4-380K. Variable temperature single-crystal conductivity measurements reveal a room-temperature conductivity near 10(-5) S cm(-1) and provide a calculated band gap of 0.72 eV. The structural results and transport properties are interpreted in the light of Extended Hückel band structure calculations.
authors.affiliation: Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1 Canada.
authors.forename: J F
authors.initials: JF
authors.lastname: Britten
authors.forename: O P
authors.initials: OP
authors.lastname: Clements
authors.forename: A W
authors.initials: AW
authors.lastname: Cordes
authors.forename: R C
authors.initials: RC
authors.lastname: Haddon
authors.forename: R T
authors.initials: RT
authors.lastname: Oakley
authors.forename: J F
authors.initials: JF
authors.lastname: Richardson