Bis(3,5-di-t-butyl-1,2-benzoquinone 1-oximato)copper(II), Cu(ox)2, and its mixed-ligand complexes, Cu(ox)Lx [Lx = 8-hydroxyquinolinato (L1), N-Phenyl-salicylaldimine (L2), N-phenyl- 3,5-di-t-butylsalicylaldiminato (L3) and N-(2-hydroxyphenyl)-3,5-di-t-butylsalicyl-aldiminato (L4)], were prepared and their spectral behavior as well as redox-reactivity towards PPh3, (m-ClC6H4)3P, (m-CH3C6H4)3P and PPh2-(CH2)4-PPh2 studied by analytical and spectroscopic (IR, UV-vis, ESR) techniques and magnetic measurements. Cu(ox)2 and Cu(ox)L4 complexes prepared in air show μef values of 2.84 and 3.33 μB, respectively, and are consistent with an S= 1 and S= 3/2 ground states. Both compounds are formulated as copper(II)-radical complex exhibiting intramolecular ferromagnetic coupling between the orthogonal dx 2 -y 2 magnetic orbital of the CuII ion and that of the π-radical ligand.