The reaction of 2 equiv of the bulky ligand N,N'-bis(3,5-di-tert-butylphenyl)-1,2-phenylenediamine, H-2[L-3(PDI)], excess triethylamine, and 1 equiv of M(CH3CO2)(2)center dot 4H(2)O (M = Ni, Co) in the presence of air in CH3CN/CH2Cl2 solution yields violet-black crystals of [Ni-II(L-3(ISQ))(2)] CH3CN (1) or violet crystals of [Co(L-3)(2)] (3). By using Pd(CH3CO2)(2) as starting material, green-blue crystals of [Pd-II(L-3(ISQ))(2)]center dot CH3CN (2) were obtained. Single-crystal X-ray crystallography revealed that 1 and 3 contain ( pseudo) tetrahedral neutral molecules [M(L-3)(2)] ( M) Ni, Co) whereas in 2 nearly square planar, neutral molecules [Pd-II(L-3(ISQ))(2)] are present. Temperature-dependent susceptibility measurements established that 1 and 2 are diamagnetic ( S) 0) whereas 3 is paramagnetic with an S) 3/ 2 ground state. It is shown that 1 contains two pi radical benzosemiquinonate(1-)-type monoanions, ((L-3(ISQ))(1-center dot), S-rad = 1/2), and a central Ni(II) ion (d(8); S = 1) which are antiferromagnetically coupled yielding the observed S-t = 0 ground state. This result has been confirmed by broken symmetry DFT calculations of 1. In contrast, the S-t = 3/2 ground state of 3 is more difficult to understand: the two resonance structures [Co-III(L-3(ISQ))(L-3(PDI))] <-> [Co-II(L-3(PDI))(L-3(IBQ))] might be invoked ( for tetrahedral [ CoII( 3LISQ) 2] containing an S Co) 3/ 2 with two antiferromagnetically coupled d- radical ligands an S-t = 1/2 is anticipated). Complex 2 is diamagnetic (S = 0) containing a Pd-II ion (d(8), S-Pd = 0 in an almost square planar ligand field) and two antiferromagnetically coupled ligand radicals (S-rad = 1/2). The electrochemistry and spectroelectrochemistry of 1, 2, and 3 have been studied, and electron-transfer series comprising the species [M(L)(2)](z) (z = 2+, 1+, 0, 1-, 2-) have been established. All oxidations and reductions are ligand centered.