Some new radical-cation salts based on unsymmetrical tetraheterofulvalenes: (MDTTTF) 4Pt(CN) 4, the first κ-phase salt, with a square planar dianion

Abstract

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 κ-(MDTTTF) 4Pt(CN) 4 (CH 2Cl 2) phase constitutes the first κ-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 κ-(MDTTTF) 4Pt(CN) 4 are similar to those of (MDTTTF) 2AuI 2, 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 κ salts. An explanation of the origin of these different behaviours is proposed.