Structure, optical and electro-physical properties of tetramerized anion-radical salt (N-Xy-Qn)(TCNQ)2

The (N-Xy-Qn)(TCNQ)(2) anion-radical salt characterized by tetramerized stacks of the TCNQ acceptor molecules has been synthesized and characterized using vibrational spectroscopy and electrical resistivity measurements. The bond lengths analysis based on the crystal structure data, indicates that the TCNQ molecules are non-uniformly charged with -0.83 e localized on the inner B molecules and -0.33 e on the outer A molecules within ABBA tetramers. Both infrared and Raman spectra of (N-Xy-Qn)(TCNQ)(2) are dominated by vibrational modes of TCNQ and display splitting related to the tetramerized structure. Many of these features are affected by the strong electron-molecular vibration (EMV) coupling. Other charge-sensitive modes allowed estimation of charge localized on TCNQ, with the results that confirm the charges estimated on basis of the crystal data. Electrical measurements revealed the low-conducting behavior with room temperature conductivity value of 2.6 mS cm(-1) and temperature dependence of resistivity that can be explained within the band conduction model. The calculated activation energies range from 0.169 eV to 0.187 eV, depending on the crystallographic direction and thermal history of the sample. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The (N-Xy-Qn)(TCNQ)(2) anion-radical salt with tetramerized stacks of TCNQ acceptor molecules was successfully synthesized and characterized using vibrational spectroscopy and electrical resistivity measurements. Analysis of the crystal structure data revealed non-uniform charge distribution, with -0.83 e localized on the inner B molecules and -0.33 e on the outer A molecules. The infrared and Raman spectra were dominated by TCNQ vibrational modes and exhibited splitting related to the tetramerized structure. The material exhibited low-conducting behavior with a room temperature conductivity of 2.6 mS cm(-1), and the temperature dependence of resistivity could be explained by the band conduction model. The estimated charge distribution based on crystal data was confirmed by other charge-sensitive modes.