Magnetic single-component molecular conductors exhibiting strong π– d interactions

Abstract

Single-component molecular conductors [M(tmdt) 2] (tmdt = trimethylenetetrathiafulvalenedithiolate; M = Ni, Au, Pt, Cu), exhibit a variety of electromagnetic properties, which originate from the differences of the metal’s d-orbitals role in the band structure formation. The [Au(tmdt) 2] crystal undergoes an antiferromagnetic transition at 110 K, while maintaining a metallic state at lower temperatures. The Au analog has a high magnetic transition temperature as compared to traditional magnetic molecular conductors due to the strong three-dimensional (3-D) structure and the contribution of the metal d-orbitals. The single-component molecular conductor, [Cu(tmdt) 2], with π- and d-like frontier orbitals is isostructural with other metallic [M(tmdt) 2] systems (M = Ni, Pt, Au). The Cu(tmdt) 2 molecule is planar, which strikingly contrasts the tetrahedral coordination of Cu(dmdt) 2 (dmdt = dimethyltetrathiafulvalenedithiolate) with similarly extended TTF type ligands. Interestingly, unlike other [M(tmdt) 2] with metallic behavior, [Cu(tmdt) 2] shows semiconducting behavior at room temperature ( σ(RT) = ∼7 S cm −1). The RT conductivity increased linearly with increased pressure to 110 S cm −1 at 15 kbar despite the compressed pellet sample. The magnetic susceptibility indicates one-dimensional (1-D) Heisenberg behavior with J = 117 cm −1 and shows antiferromagnetic ordering at 13 K. The [Cu(tmdt) 2] is a new multi-frontier π– d system, which introduces a d( σ)-type frontier orbital around the Fermi level of the π-like metal bands.