SOME NEW RADICAL-CATION SALTS BASED ON UNSYMMETRICAL TETRAHETEROFULVALENES - (MDTTTF)4PT(CN)4, THE 1ST KAPPA-PHASE SALT, WITH A SQUARE-PLANAR DIANION

We report the synthesis of the organic donor radical cations, methylenedithiotetrathiafulvalene (MDTTTF), ethylenedithiotetrathiafulvalene (EDTTTF) and vinylenedithiotetrathiafulvalene (VDTTTF), with the square planar dianions, Pt(CN)4 and Ni(CN)4. Among these salts, the kappa-(MDTTTF)4Pt(CN)4 (CH2Cl2) Phase constitutes the first kappa-phase, produced with a nonlinear dianion. Crystal and electronic structures, electrical and optical properties and ESR measurements have been investigated for these salts. Crystal and electronic structures of kappa-(MDTTTF)4Pt(CN)4 are similar to those Of (MDTTTF)2AuI2, Which is an ambient pressure superconductor (T(c)=4.5 K). However, d.c. conductivity measurements show a semiconducting behaviour, associated with an ESR linewidth decreasing with temperature in contrast with all other known kappa-salts. An explanation of the origin of these different behaviours is proposed.