Mixed valence trimers in cation radical salts of TMTTF with the planar bis(6-sulfo-8-quinolato) platinum complex [Pt(qS)2]2−

Abstract

Electrocrystallization of TMTTF (tetramethyltetrathiafulvalene) in the presence of the dianionic [Pt(qS)₂]²⁻ platinum complex (qS: 5-sulfo-8-quinolinol) afforded simultaneously two phases. Phase A with isolated dicationic (TMTTF)₂²⁺ species is fully insulating and characterized by C–H hydrogen bonds with the anionic sulfonate moieties. Phase B is a mixed valence salt formulated as (TMTTF)₃[Pt(qS)₂]. It is organized into strongly trimerized chains, with a notably higher conductivity (σ_RT = 4 × 10⁻⁵ S cm⁻¹). The charge distribution within the TMTTF trimers has been evaluated from the intramolecular bond distances, and IR and Raman spectra, converging all to a +0.5/+1/+0.5 motif, which is not modified at lower temperatures. Spectroscopic studies of such trimeric structures are scarce and the doublet (or triplet) structure expected in the IR of trimers is clearly identified here in the EMV-activated ν₈(a_g) mode associated with the totally symmetric vibration of methyl groups, in relation to the weak C–H⋯O hydrogen bonds between the radical cation and the dianionic [Pt(qS)₂]²⁻ platinum complex.