Iminosemiquinone complexes of copper have been prepared by treating Cu metal with 2,4,6,8-tetra-tertbutylphenoxazin- 1-one (PhenoxBQ). Reactions carried out with PPh(3) gave Cu-1(PPh(3))(2)(PhenoxSQ). Crystallographic characterization of crystals obtained as the acetonitrile solvate (triclinic, P1 $($) over bar$$, a 11.414(2) Angstrom, b = 15.431(2) Angstrom, c = 17.999(3) Angstrom, alpha = 92.88(1)degrees, beta = 94.21(1)degrees, gamma = 109.84(1)degrees, V = 2964.4(8) Angstrom 3, Z = 2, R = 0.064) has shown that the coordination geometry is tetrahedral, EPR spectra indicate that the unpaired electron is ligand-based, and electrochemical properties consist of one-electron oxidation and reduction reactions at the iminoquinone ligand. Reactions carried out in the absence of coligand or in the presence of a nitrogen-donor coligand gave Cu-II(PhenoxSQ)(2), Crystallographic characterization of crystals obtained as the dichloromethane solvate (monoclinic, C2/c, 28.40(2) Angstrom, 12.946(4) Angstrom, a = 20.552(12) Angstrom, beta = 129.32(4)degrees, V = 5846(6) Angstrom 3, R = 0.070) has shown that the molecule has a distorted tetrahedral structure. Electrochemical characterization has indicated that the complex undergoes two one-electron oxidations and two one-electron reductions, all occurring at the iminoquinone ligands. EPR spectra and variable-temperature magnetic measurements indicate that exchange between PhenoxSQ ligands is ferromagnetic, while Cu-PhenoxSQ exchange is antiferromagnetic. At low temperature, the complex has a ligand-based S = 1/2 magnetic ground state.