Doping o
f spin-ladder systems by isostructural paramagnetic complexes was attempted. Despite the close isostructuralnature o
f the pure (DT-TTF)
2[M(mnt)
2] (M = Au, Ni, Pt) end-members, which present a ladder structure, doping o
fthe spin-ladder (DT-TTF)
2[Au(mnt)
2] with either 5% or 25% [M(mnt)
2]
- (M = Ni, Pt) generates two (metrically)
newphases. Their markedly di
fferent crystal structures have been determined using laboratory X-ray powder di
ffractiondata. (DT-TTF)
2[Au
0.75Ni
0.25(mnt)
2] consists o
f a mixed-valence compound (o
f triclinic symmetry), which was onlydetected, pure or in a mixture o
f phases, when [Ni(mnt)
2]
- was used as a dopant. Di
fferently, the stoichiometric1:1 [DT-TTF][Au
0.75Pt
0.25(mnt)
2] monoclinic phase was
found when [Pt(mnt)
2]
- (in 5% and 25%) was employed asthe doping agent. Remarkably, only in the 5% Pt doping experiment, the major component o
f the mixture was theladder structure compound (DT-TTF)
2[Au(mnt)
2] doped with minor amounts o
f Pt. This 5% Pt-doped specimenshows an EPR signal (
g = 2.0115,
![](/images/gi<font color=)
fchars/Delta.gi
f" BORDER=0 >
Hpp = 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 o
f the 5%Pt-doped composition at high temperatures are comparable to those o
f (DT-TTF)
2[Au(mnt)
2] with room-temperatureconductivity
![](/images/gi<font color=)
fchars/sigma.gi
f" BORDER=0 >
300K = 13 S/cm and thermopower
S300K = 46
![](/images/entities/mgr.gi<font color=)
f">V/K, with a sharp transition at 223 K similar to thatpreviously observed in the Cu analogue at 235 K.