Syntheses and structural characterization of new heteroleptic 1,1′-bis(diphenylphosphino)ferrocene-dithio complexes of Ni, Pd and Pt: Their uses as sensitizers in TiO2 dye sensitized solar cells

A series of new heteroleptic complexes of the form [M(dppf)L] [where dppf = 1,1′-bis(diphenylphosphino)ferrocene; M = Ni(II) (1), Pd(II) (2), Pt(II) (3) and L = p-tolylsulfonyl dithiocarbimate, p-CH3C6H4SO2NCS2; M = Ni(II) (4), Pd(II) (5), Pt(II) (6) and L = p-chlorobenzene sulfonyl dithiocarbimate, p-ClC6H4SO2NCS2; M = Ni(II) (7), Pd(II) (8) and L = p-bromobenzene sulfonyl dithiocarbimate, p-BrC6H4SO2NCS2; M = Ni(II) (9), Pd(II) (10) and L = 1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolate (ecda), C2H5OCO(CN)CCS2] have been synthesized and characterized by elemental analysis, spectroscopy (IR,1H, 13C and 31P NMR and UV–Vis.), cyclic voltammetry and single crystal X-ray diffraction and their light harvesting properties have been investigated by using them as photosensitizers in dye sensitized TiO2 solar cells. In these complexes the metal lies at the center of a distorted square planar environment; the distortion varies in the order Pd ≈ Pt > Ni. Among these, the nickel complexes showed light-to-electrical energy conversion efficiencies close to that shown by Ru dye N719 whereas the corresponding palladium and platinum complexes show inferior efficiencies under similar experimental conditions.