Proton Transfer and a Dielectric Phase Transition in the Molecular Conductor (HDABCO⁺)₂(TCNQ)₃

Abstract

One-dimensional dielectric (N.H.N)( infinity ) hydrogen-bonding chains of monoprotonated 1,4-diazabicyclo[2.2.2]octane (HDABCO(+)) were introduced into an electrically conducting 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) salt as the countercation structure. Room-temperature electrical conductivity was approximately 10(-)(3) S cm(-)(1), with a semiconductive behavior. The temperature-dependent dielectric constants of (HDABCO(+))(2)(TCNQ)(3) indicated a dielectric transition at 306 K. A large deuterium isotope effect for the dielectric transition (DeltaT = 70 K) was observed for the deuterated salt, (DDABCO(+))(2)(TCNQ)(3). Thermally activated order/disorder of the protons or deuteriums within the one-dimensional hydrogen-bonding chains of (HDABCO(+))( infinity ) and (DDABCO(+))( infinity ) affected the dielectric responses in the TCNQ-based semiconductors.