New Te-based counter anions for conducting cation radical salts: tetraiodotellurate(II) and hexaiododitellurate(II)

Synthesis, structure, and resistivity measurements of several cation radical salts formed by the organic donors TMTTF, EDT-TTF, ET and BETS with new Te-based planar dianions, TeI42− and Te2I62− are reported. The anion sheets in these salts consist of discrete mono- or dinuclear anions. Crystal structure of (ET)4TeI4 (1) is based on the “herring bone” arrangement of ET molecules, similar to the α-type. Compound 1 is a semiconductor (ρr.t.=0.5 Ω cm) and shows a transition to the insulating state at 210 K. (ET)5Te2I6 (2) consists of alternating arrangement of the θ-type donor layer and the checker-like anion sheet. With decreasing temperature, the resistivity of 2 (ρr.t.=2 Ω cm) shows a gradual increase followed by a sharp upturn at 110 K. (BETS)5Te2I6 (3) is isostructural with 2. This salt is metallic down to 120 K (ρr.t.=0.02 Ω cm), and shows a gradual increase of the resistivity followed by a clear transition to the insulating state at about 60 K.