Molecular conductors based on peri-ditellurium-bridged donors, 2,3-DMTTeA and TMTTeN

Molecular conductors based on peri-ditellurium-bridged polyacene donor molecules 3,4-dimethylanthra[1,9-cd:4,10-c′d′]bis[1,2]ditellurole (2,3-DMTTeA) and 2,3,6,7-tetramethylnaphtho[1,8-cd:4,5-c′d′]bis[1,2] ditellurole (TMTTeN) were prepared. The crystal structure analyses of neutral 2,3-DMTTeA molecule and its cation radical salts revealed that these crystals involve an orientational disorder of the asymmetrical molecule, 2,3-DMTTeA, and that the intermolecular network through tellurium atoms is very strong and dominant in terms of the construction of the crystal frameworks. In the crystal of (TMTTeN)₂M(CN)₂ (M = Ag and Au), the crystal structure analyses and the extended Hückel tight-binding band calculations indicated that these salts are quasi three-dimensional conductors. These salts are highly conductive (720-760 S cm^-1) and maintain metallic states down to about 50 K. Furthermore, the Ag(CN)₂^- salt exhibited a Pauli paramagnetic behavior down to 2 K [χ(para) ≈ 2.0-2.5 × 10^-4 emu mol^-1]. In the crystal of (TMTTeN)(SCN) _0.88, the donor molecules are stacked to form one-dimensional columns and construct a three-dimensional network between the columns through the intermolecular Te⋯Te contacts. The SCN^- salt is also highly conductive (590 S cm^-1) and maintains a metallic behavior down to 4.2 K. Almost temperature-independent paramagnetic susceptibility of (TMTTeN)(SCN)_0.88 indicates Pauli paramagnetism of this salt [χ(para) ≈ 1.6-1.9 × 10^-4 emu mol^-1]. A tight-binding band structure calculation indicates that the Fermi surface of the SCN^- salt is open along the b* and c* directions, but the intermolecular interactions between the donor columns are not so weak because of the three-dimensional network mediated by the protruded tellurium atoms.