Electronic and Structural Characterization of A Charge-transfer Crystal With Strong Electronic Correlations Through Infrared and Raman-spectroscopy - Tmpd-tcnqf4

The electronic and structural characterization of the title charge transfer (CI) complex is carried out mainly by the exploitation of the infrared powder spectrum and its temperature dependence from room temperature to 15 K as well as of the Raman powder spectrum at 15 K. The infrared spectrum shows that the complex has a fully ionic electronic ground state (ρ≂1) and the analysis of the spectroscopic effects due to the radical electron–intramolecular vibration interactions reveals a structure built up of segregated stacks of TMPD and TCNQF4. Moreover, this analysis shows that the TCNQF4 stacks are nonregular in the whole studied temperature range, whereas, by lowering temperature, the TMPD stacks undergo a phase transition from a regular to a nonregular structure with onset at about 180 K. The effective on‐site electronic correlation parameter, the hopping integral, and the magnetic gap of both stacks in the nonregular phase are estimated by adopting a cluster model made up of a dimeric unit to describe the stacks and by comparison with known materials. On the same basis, the temperature dependence of the hopping integrals is also estimated. The collected information, considered in the light of the Peierls–Hubbard model, suggests that TMPD–TCNQF4 can be considered a compound with strong electronic correlations.