Chemical preparation and physical properties of a metallic organic charge transfer complex : HMTTF-TCNQ

A new chemical preparation of hexamethylenetetrathiofulvalenium and of the HMTTF-TCNQ charge transfer complex is described. The d.c. conductivity has been measured as a function of temperature; it shows a broad maximum (Tmax ≃ 75 K) followed by two transitions (T c1 = 49 ± 1 K, Tc2 = 43 ± 1 K). The static paramagnetism, E.P.R. and specific heat have been measured; they indicate that T c2 must be associated with the appearance of a periodic lattice distortion of the HMTTF chains which (dominate observed behaviour). The line-width is determined by interactions between chains which are more efficient in this compound than in TTF-TCNQ, in agreement with the behaviour of the electrical conductivity.