Single crystals of the quasi-one-dimensional conductors (Per)2M(mnt)2 (Per = perylene, M = Ni and Cu, mnt = maleonitrile dithiolate or cis-2,3-dimercapt~2-butened~i~le) were prepared by electrocrystallimtion. In addition to the previously reported &phase with semiconducting properties (uRT H 50 i2-I cm-I, SRT = 22 p V K-I), a second phase with metallic properties, denoted a, was also obtained. The a-and @-phases differ by their crystallographic structure. A temperature-independent superlattice modulation stabilizing the 66 periodicity in the chain direction characterizes the 8-phases. The crystal structure of the metallic a-phase consists of a close-packed arrangement of uniform stacks of segregated perylene and M(mnt)2 units. At rwm temperature, the electrical conductivity along the stacking axis is URT H 700 i2-I cm-' and the absolute thermoelectric power has a positive value of S R T = 35 pV K-I. Both the Ni and Cu derivatives exhibit a metallic behavior down to 25 and 32 K, respectively, where a metal-insulator transition occurs.