Spectroscopic characterization of (BEDT-TTF)2[Pt(S2C4O2)2] charge density wave ground state

Abstract

We report a detailed spectroscopic characterization of the charge transfer (CT) complex between bis(ethylendithio)tetrathiafulvalene (BEDT-TTF) and bis(dithiosquarate)platinate(II), (BEDT-TTF) 2 [Pt(S 2 C 4 O 2 ) 2 ]. In this complex BEDT-TTF dimers are separated by the [Pt(S2C4O2)2] 2– anions, forming a quasi-one-dimensional stack. We show that the stack structure is stabilized by CT between BEDT-TTF dimers and between BEDT-TTF and [Pt(S 2 C 4 O 2 ) 2 ]. Two CT transitions, polarized along the stack axis, are identified in the optical spectra. Furthermore, the average charge on the molecules is not a multiple integer, and the amplitude of the intrinsic ground state charge density wave (CDW) can be represented as: …[Pt(S 2 C 4 O 2 ) 2 ] 1.8– BEDT-TTF 0.9+ BEDT-TTF 0.9+ [Pt(S 2 C 4 O 2 ) 2 ] 1.8– … The optical spectra polarized along the (BEDT-TTF) 2 [Pt(S 2 C 4 O 2 ) 2 ] stack are well reproduced by a semiempirical model which takes into account the coupling of BEDT-TTF molecular vibrations with the CT electrons (e-mv coupling). Under pressure, (BEDT-TTF) 2 [Pt(S 2 C 4 O 2 ) 2 ] undergoes two distinct phase transitions in the ranges 1-1.6 and 2.2-2.5 GPa, the first involving a stack distortion.