NEW CONDUCTING RADICAL-CATION SALTS BASED ON BEDTTF AND TETRACYANOMETALLATES SQUARE-PLANAR DIANIONS [M(CN)42-, M=PT(II), NI(II)]

The BEDTTTF salts based on tetracyanometallate dianions exhibit a rich polymorphism giving rise to semiconductor, metallic and even supercon ductor materials. New (BEDTTTF)4M(CN)2(H2O)x (M=Ni, Pt ; x=0-->4) phas es were prepared. The stoichiometries have been determined by X ray an alysis and agree well with the TGA (theromo-gravimetric analysis) resu lts. These salts are isostructural and show a conductor-insulator tran sition at low temperature. A single crystal structure on the Ni (x=4) salt has been carried out. Crystals belong to the monoclinic space gro up P2/c with a=17.403(4), b=6.767(9), 15.030(3), beta=109.26(2), R=0.0 5 for 2795 reflexions. The ESR line width dependence on temperature re vealed a phase transition at about 180K. These phases an highly locali sed and present good candidates for a low temperature Peierls transiti on.