Syntheses and crystal structures of the molecular conductors Z[Pd(dmit)2]2 {Z = (Me3NEt)+, (MeNEt3)+, (NEt4)+} and their precursors Z2[Pd(dmit)2]

Abstract

Electrically conductive platelet crystals of Z[Pd(dmit)₂]₂ [Z = (Me₃NEt)⁺, (MeNEt₃)⁺, (NEt₄)⁺], as well as their precursors Z₂[Pd(dmit)₂], have been synthesized by a non-electrochemical method and their structures have been determined. The single-crystal conductivities at a direction on the cleavage surface at room temperature were measured to be 58 Ω⁻¹ cm⁻¹ for (Me₃NEt)[Pd(dmit)₂]₂, 5.0 Ω⁻¹ cm⁻¹ for (MeNEt₃)[Pd(dmit)₂]₂ and 2.2 Ω⁻¹ cm⁻¹ for (NEt₄)[Pd(dmit)₂]₂, respectively. This sequence of conductivity is agreement with the sequence of structural two-dimensionality of these three complexes. The resistivity–temperature curves reveal the semiconducting behavior of the above complexes, which show very narrow band gaps. The structure analysis results reveals that when the size of cation Z in Z[Pd(dmit)₂]₂ is finely tuned [(Me₄N)⁺ → (Me₃NEt)⁺ → (Me₂NEt₂)⁺ → (MeNEt₃)⁺ → (NEt₄)⁺], the corresponding complexes belong to the same structural motif and each individual possesses some special structural characteristics. Subtle structural difference in this group of complexes can severely influence their measured conductivities and significantly influence their calculated band structures.