The compound of formula (rad)(2)Mn-2[Cu(opba)](3)(DMSO)(2).2H(2)O (hereafter abbreviated as (rad)(2)Mn2Cu3) has been synthesized; rad(+) stands for the radical cation 2-(1-methylpyridinium-4-yl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, and opba stands for o-phenylenebis(oxamato). The crystal structure has been solved (space group, Cc; lattice parameters, a = 25.379(3) Angstrom, b = 25.146(3) Angstrom, c = 18.845(6) Angstrom, beta = 131.52(4)degrees, Z = 4) and has revealed quite an unusual architecture. The structure consists of two nearly perpendicular graphite-like networks with edge-sharing hexagons. The corners of each hexagon are occupied by Mn(II) ions, and the middles of the edges by Cu(II) ions. The two networks are interlocked, the center of each hexagon being occupied by a Cu(II) ion belonging to a perpendicular hexagon. (rad)(2)Mn2Cu3 contains three kinds of spin carriers : Mn(II) and Cu(II) ions, antiferromagnetically coupled through oxamato bridges, and rad(+) radical cations, bridging the Cu(II) ions through the nitronyl nitroxide groups and forming rad(+)-Cu(II) chains. The magnetic and EPR properties of (rad)(2)Mn2CU3 have been studied in some detail. The temperature dependence of chi(M) T (chi(M) being the molar magnetic susceptibility and T the temperature) shows a minimum around 115 K characteristic of a ferrimagnetic behavior and then a divergence as T approaches the very low temperatures. The temperature dependence of the magnetization has confirmed that a long-range magnetic ordering occurs at T-c = 22.5 K. The field dependence of the magnetization, M = f(H), has been measured at 4.2 K up to 200 kOe. : Mn(II) and Cu(II) ions, antiferromagnetically coupled through oxamato bridges, and rad(+) radical cations, bridging the Cu(II) ions through the nitronyl nitroxide groups and forming rad(+)-Cu(II) chains. The magnetic and EPR properties of (rad)(2)Mn2CU3 have been studied in some detail. The temperature dependence of chi(M) T (chi(M) being the molar magnetic susceptibility and T the temperature) shows a minimum around 115 K characteristic of a ferrimagnetic behavior and then a divergence as T approaches the very low temperatures. The temperature dependence of the magnetization has confirmed that a long-range magnetic ordering occurs at T-c = 22.5 K. The field dependence of the magnetization, M = f(H), has been measured at 4.2 K up to 200 kOe.