Electrocrystallisation of the p-electron donor dithiopheno-tetrathia- fulvalene (DT-TTF) with maleonitrile dithiolate (mnt) - metal (M) complexes gives rise to the new family of radical ion salts ((DT-TTF)2M(mnt)2 )( MaAu, Pt, Ni), which are isostructural and crystal- lise in the monoclinic space group P21/n forming regular segregated stacks of donor and acceptor molecules along the b axis. The DT-TTF stacks are paired and interact strongly through S ··· S contacts in a ladder-like motif. The three salts have quite high room-temperature electrical conductivities (9, 40 and 40 S cm ˇ1 for Ma Au, Pt and Ni respec- tively) but their conductivity - tempera- ture dependencies differ. The Au salt has an activated conductivity at room temperature whereas the Ni and Pt salts are metal-like at room temperature and both exhibit a metal - insulator transi- tion around 120 K. These contrasting transport properties are accounted for by the differences in the transfer inte- grals along the DT-TTF stacks. The magnetic susceptibility of the salt with Ma Au, in which the (Au(mnt)2 ˇ ) anion is diamagnetic, can be fitted to a two- legged spin-ladder model. From diffuse X-ray scattering studies it is established that below 220 K the donors dimerise along the b stacking direction, and the spin carrier units in the ladder are identified as those formed by dimerised donors ((DT-TTF)2) a . . Observation in their EPR spectra of a single line which increases dramatically in width as the conductivity increases is evidence for the presence of two magnetic subsys- tems which interact in the salts (Ma Ni, Pt) with paramagnetic (M(mnt)2) ˇ ions.