SPECTRAL AND ELECTROPHYSICAL PROPERTIES OF ANION-RADICAL SALTS OF TCNQ AND METHYL-TCNQ WITH N-ALKYLPIRAZINIUM CATIONS

摘要

Anion-radical salts (ARS) of 7,7,8,8- tetracyanoquinodimethane (TCNQ) and methyl-TCNQ (MTCNQ) of composition [N-(C_nH_(2n+1))-Pz](TCNQ)_m and [N-(C_nH_(2n+1))-Pz](MTCNQ)_m, with Pz for pirazinium, n = 1, 2, ... 5 and m = 1, 2 have been synthesized and investigated. The IR absorption spectra of these compounds have been studied at room temperature. For single crystal and pellet samples of the synthesized salts, electric conductivity has been measured in the temperature range of 77 - 300 K, and the basic electrophysical characteristics were determined. The [N-CH_3-Pz](TCNQ) compound was revealed to be an organic metal undergoing a metal-dielectric transition when cooled below 120 K, the lowest temperature which has ever been achieved for ARS of TCNQ with close-type cations. The conductivity of [N-(C_nH_(2n+1))-Pz](MTCNQ)_m salts has been found to be substantial and comparable with that of analogous TCNQ-based compounds. In this, the above compounds are noticeably distinguished from the ARS with cations based on other nitrogen-containing heterocycles. In crystals of the [N-C_2H_5-Pz](MTCNQ)_2 salt, the existence of a highly quasi-two-dimensional conducting state is expected, despite this being atypical for TCNQ-based ARS.