Conductivity in Thin Films of Transition Metal Coordination Complexes

Two coordination complexes have been made by combining the dithiolene complexes [M(mnt)₂]^2- (mnt = maleonitriledithiolate; M = Ni²⁺ or Cu²⁺) as anion, with the copper(II) coordination complex [Cu(Stetra)] (Stetra = 6,6'-bis(4,5-dihydrothiazol-2-yl)-2,2'-bipyri-dine) as cation. The variation of the metal centers leads to a dramatic change in the conductivity of the materials, with the M = Cu²⁺ variant (Cu-Cu) displaying semiconductor behavior with a conductivity of approximately 2.5 × 10^-8 S cm^-1, while the M = Ni²⁺ variant (Ni-Cu) displayed no observable conductivity. Computational studies found Cu-Cu enables a minimization of reorganization energy losses and, as a result, a lower barrier to the charge transfer process, resulting in the reported higher conductivity.