Bilayer conducting salts with polymeric anions

Abstract

Five new salts of 5-cyanobenzene-ethylenedithio-tetrathiafulvalene (CNB-EDT-TTF), with general formula (CNB-EDT-TTF)₄A, and anions A= Ag(CN)₂ (1), Ag(CN)₂•H₂O (2), Ag₂(CN)₃ (3), Ag(SCN)₂ (4) and Hg₂(SCN)₅ (5), were prepared by electrocrystallisation and characterised by single crystal X-ray diffraction, electrical conductivity, thermoelectric power and magnetic susceptibility measurements. Their crystal structure is based on a double layer arrangement of the donors with a β” packing patern identical to that previously observed in related salts with small discrete anions. The donor bilayers are separated by layers of anions which however are incoherently arranged perpendicularly to the layers. The average structures obtained are compatible with anionic arrangements similar to those previously observed in single layer salts of BEDT-TTF and related donors, where with exception of 1 the anions are polymeric. While 2 presents an electrical resistivity with a thermally activated regime, 1, 3, 4 and 5 show a metallic behaviour at high temperatures with room temparature values in the range 10-20 S/cm and sample dependent electronic localisation effects at lower temperatures. Thermoelectric power of these compounds is +82 -90 μV/K at room temperature, following a behavior identical to the analogues with small discrete anions. The paramagnetic susceptibility of 4 and 5, similarly to that of the analogues with I₃, PF₆, AsF₆ and ReO₄ anions, present values of ≈1.0x10 ^-3 emu/mol at room temperature, significantly enhanced compared with the Pauli-type contribution predicted from electron band calculations.