title: Structural, magnetic, and electrical characterization of new polycrystalline phases of nickel- and platinum-doped [(DT-TTF)n][Au(mnt)2] (n = 1, 2).
abstract: Doping of spin-ladder systems by isostructural paramagnetic complexes was attempted. Despite the close isostructural nature of the pure (DT-TTF)2[M(mnt)2] (M = Au, Ni, Pt) end-members, which present a ladder structure, doping of the spin-ladder (DT-TTF)2[Au(mnt)2] with either 5% or 25% [M(mnt)2]- (M = Ni, Pt) generates two (metrically) new phases. Their markedly different crystal structures have been determined using laboratory X-ray powder diffraction data. (DT-TTF)2[Au0.75Ni0.25(mnt)2] consists of a mixed-valence compound (of triclinic symmetry), which was only detected, pure or in a mixture of phases, when [Ni(mnt)2]- was used as a dopant. Differently, the stoichiometric 1:1 [DT-TTF][Au0.75Pt0.25(mnt)2] monoclinic phase was found when [Pt(mnt)2]- (in 5% and 25%) was employed as the doping agent. Remarkably, only in the 5% Pt doping experiment, the major component of the mixture was the ladder structure compound (DT-TTF)2[Au(mnt)2] doped with minor amounts of Pt. This 5% Pt-doped specimen shows an EPR signal (g = 2.0115, DeltaHpp = 114 G at 300 K) wider than the pure compound (DT-TTF)2[Au(mnt)2], denoting exchange between the donor spins and Pt(mnt)2- centers. The electrical transport properties of the 5% Pt-doped composition at high temperatures are comparable to those of (DT-TTF)2[Au(mnt)2] with room-temperature conductivity sigma300K = 13 S/cm and thermopower S300K = 46 microV/K, with a sharp transition at 223 K similar to that previously observed in the Cu analogue at 235 K.
authors.affiliation: Institut de Ciència de Materials de Barcelona, CSIC, Campus de la UAB, E-08193 Bellaterra, Spain.
authors.forename: Xavi
authors.initials: X
authors.lastname: Ribas
authors.forename: Angelo
authors.initials: A
authors.lastname: Sironi
authors.forename: Norberto
authors.initials: N
authors.lastname: Masciocchi
authors.forename: Elsa B
authors.initials: EB
authors.lastname: Lopes
authors.forename: Manuel
authors.initials: M
authors.lastname: Almeida
authors.forename: Jaume
authors.initials: J
authors.lastname: Veciana
authors.forename: Concepció
authors.initials: C
authors.lastname: Rovira