Studies on the structure and conduction mechanism of (Acrd)[Au(mnt)₂]_2.7 and (Phenz)[Au(mnt)₂]₃ molecular single crystals

Abstract

Studies on the structure and conduction mechanism of (Acrd)[Au(mnt) 2 ] 2.7 and (Phenz)[Au(mnt) 2 ] 3 Two quasi-one-dimensional acridinium (Acrd) and phenazinium (Phenz) molecular conductors with a single anion of maleonitriledithiolato aurate (Au(mnt) 2 ) were obtained by electrochemical crystallization. The Acrd single crystal was found to have a non-stoichiometric composition donor (D): acceptor (A) = 1 : 2.7, whereas the Phenz single crystal was found to have a stoichiometric composition D : A = 1 : 3. Crystal structure analysis revealed that the former has a monoclinic lattice with a = 9.26, b = 7.63, c = 27.76, β = 104.8, Z = 2, and the latter has a monoclinic lattice with a = 17.06, b = 14.46, c = 28.30, β = 108.3, Z = 6. The Acrd radicals were assumed to form alternate stacking with the anion sublattice due to the appearance of satellite reflections indicating a sinusoidal modulation structure. The Phenz single crystal was verified as adopting cation stacks with disorder in the anion sublattice. The results were supported by FTIR spectroscopy and cyclovoltammetry measurements. The room temperature dc conductivity of the Phenz crystal was found to be about two orders of magnitude higher than that of the Acrd crystal. A quasi-one-dimensional conduction mechanism was proposed for the Phenz crystal but a conventional nearest-neighbour hopping mechanism was shown to best describe conduction in the Acrd single crystal exhibiting a well-defined metal-to-insulator transition.