Iodine charge-transfer salts of benzene-bridged bis(1,2,3,5-diselenadiazolyl) diradicals. Electrocrystallization and solid-state characterization of 1,3- and 1,4-[(Se2N2C)C6H4(CN2Se2)][I]

Electroreduction of 1,3- and 1,4-benzene-bridged bis(diselenadiazolium) salts [1,4-Se][SbF6](2) and [1,4-Se][SbF6](2) in acetonitrile, at a Pt wire and in the presence of iodine affords the 1:1 charge-transfer salts [1,4-Se][I] and [1,3-Se][I]. Crystals of [1,4-Se][I] belong to the monoclinic space group C2/m, with FW = 598.9, a = 10.586(2), b = 16.713(2), c = 3.5006(14) Angstrom, beta = 104.26(2)degrees, V = 600.2(3) Angstrom(3), Z = 2. Crystals of [1,3-Se][I] belong to the orthorhombic space group Ima2, with FW = 598.9, a = 28.489(7), b = 3.543(2), c = 12.283(2) Angstrom, V = 1239.8(8) Angstrom(3), Z = 4. In the presence of an excess of iodine, electrocrystallization of [1,4-Se](2+) affords the mixed iodide/triiodide salt [1,4-Se][I][I-3], space group C2/c, FW = 979.59, a = 12.862(3), b = 15.063(2), c = 9.028(3) Angstrom, beta = 100.62(2)degrees, V = 1719.1(7) Angstrom(3), Z = 4. The structures of the two 1:1 compounds consist of perfectly superimposed stacks of molecular units interspersed by columns of disordered iodines. Interstack contacts in both structures are limited, indicative of 1-dimensional electronic structures. Variable-temperature single-crystal conductivity measurements on [1,4-Se][I] reveal weakly metallic behavior at room temperature, with a phase transition to a semiconducting state occurring at about 240 K. Magnetic susceptibility measurements on [1,4-Se][I] are consistent with the conductivity data; the magnetic susceptibility of [1,3-Se][I] behaves similarly. The crystal structures and transport properties are discussed in light of extended Huckel band structure calculations.