Structural Phase Transition in (NMe4)2TCNQ3

The structural properties of a neutral/radical 1 : 2 mixed compound, (NMe4)2TCNQ3, have been studied by the X-ray diffraction method in a temperature range between 25 and 150 ℃. The experimental data show that a second order phase transition takes place at around 60 ℃ and that the high-temperature phase has a monoclinic C2/m structure. The molecular planes of dimerized TCNQ-· radicals, being slipped against each other in the low temperature phase, are expected from the C2/m symmetry to be totally eclipsed in the high-temperature phase. A good fit of the power law (1-T/Tc)a to the temperature variation of the intensity of the Bragg reflection arising from the slipped TCNQ-· radicals is obtained with Tc = 330.7±0.8 K and a = 0.66±0.05 for T≤Tc. Influences of this novel phase transition on the electronic properties are discussed