The change of the alkyl chain length in N,N-bis(coordinating group)-substituted oxamides was observed to be able to tune the structures of two new radical complexes[Cu2(oxen)(4-NITPhPy)2](ClO4)2 (1) [oxen = N,N-bis(2-aminoethyl)oxamide] and [Cu2(oxpn)(4-NITPhPy)2](ClO4)2·H2O (2) [oxpn = N,N-bis(2-aminopropyl)oxamide], which constructed from trans-oxamido-bridged Cu(II)–Cu(II) dinuclear building blocks and a new nitronyl nitroxide, 2-[4-(4-pyridyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPy): 1 possesses a dinuclear structure while 2 shows a 1D chain structure. The magnetic data of 1 could be analyzed using a model derived from the Cu(II)–Cu(II) dinuclear building block with two nitroxide terminal ligands, giving J1 = −286 cm−1, J2 = −6 cm−1 and θ = −3.95 K. The magnetic interactions in 2 were simulated by an appropriate uniform chain model composed of the tetraspin [Cu2-(NIT)2] units. The best fitting gives J1 = −213.5 cm−1, J2 = 19.13 cm−1 and Jc = −2.11 cm−1.