Design, Synthesis, and Structure of Copper Dithione Complexes: Redox-Dependent Charge Transfer

Redox-active ligands impart versatility in transition metal complexes, which are attractive for photosensitizers, dye sensitized solar cells, photothermal therapy, etc. Dithiolene (Dt) ligands can transition between fully reduced and fully oxidized states. Herein, we report the syntheses, characterization, crystal structures and electronic properties of four [Cu(R(2)Dt(0))(2)](+/2+) (R = Me, iPr) complexes, [Cu(iPr(2)Dt(0))(2)][PF6] (1a), [Cu(iPr(2)Dt(0))(2)][PF6](2) (1b), and [Cu(Me(2)Dt(0))(2)][PF6] (2a), [Cu(Me(2)Dt(0))(2)][PF6](2) (2b), where iPr(2)Dt(0) = N,N '-diisopropyl-1,2-piperazine dithione and Me(2)Dt(0) = N,N '-dimethyl-1,2-piperazine dithione. In addition, the molecular structure of [Cu(iPr(2)Dt(0))(2)][BF4](2)(1c) is also reported. Complexes 1a and 2a crystallized in the triclinic, P1 space group, and 1c crystallized in the monoclinic crystal system, space group C2/(c.) The single-crystal X-ray diffraction measurements show that the Cu(I) complexes have a distorted tetrahedral geometry, whereas the Cu(II) complex exhibits a true square-planar geometry. Cu(I) complexes exhibit a low energy charge-transfer band (450-650 nm), which are not observed in Cu(II) complexes. Electrochemical studies of these complexes show both ligand- and metal-based redox couples.