The ligand 2-anilino-4,6-di-tert-butylphenol and its 2-(3,5-dichloroanilino)-4,6-di-tert-butylphenol analogue react in CH(3)CN or CH(3)OH solutions with divalent transition metal ions in the presence of air and triethylamine. Depending on the metal:ligand ratio (1:1, 1:2, or 1:3) and the presence (or absence) of the cyclic amine 1,4-dimethyl-1,4,7-triazacyclononane (dmtacn), the following complexes have been isolated as crystalline solids: [Co(III)(L(ISQ))(3)] (1); [Cu(II)(dmtacn)(L(ISQ))]PF(6) (2); [Cu(II)(L(ISQ))(2)] (3); [Ni(II)(L(ISQ))(2)] (4a); [Ni(II)((Cl)L(ISQ))(2)] (4b); [Pd(II)(L(ISQ))(2)] (5). (L(ISQ))(-) represents the monoanionic o-iminobenzosemiquinonate radical (S(rad) = (1)/(2)). Compounds 1-5 have been characterized by single-crystal X-ray crystallography at 100(2) K. For all complexes it is unambiguously established that the O,N-coordinated o-iminobenzosemiquinonato(1-) ligand is present. Complexes 3, 4b, and 5 are square planar molecules which possess an S(t) = (1)/(2), 0, and 0 ground state, respectively, as was established by (1)H NMR and EPR spectroscopies and variable-temperature magnetic susceptibility measurements. Complex 2 possesses an S(t) = 1 ground state which is attained via strong intramolecular ferromagnetic coupling (J = +195 cm(-1)) between the d(x)2-(y)2 magnetic orbital of the Cu(II) ion and the pi-orbital of the ligand radical. Complex 1 contains three mutually orthogonal (L(ISQ))(-*) ligands and has an S(t) = (3)/(2) ground state. It is shown that the electronic structure of 4a and 5 is adequately described as singlet diradical containing a divalent, diamagnetic d(8) configurated central metal ion and two strongly antiferromagnetically coupled (L(ISQ))(-) radical ligands. It is concluded that the same electronic structure prevails in the classic bis(o-diiminobenzosemiquinonato)- and bis(o-benzosemiquinonato)metal complexes of Ni(II), Pd(II), and Pt(II). The electrochemistry of all complexes has been investigated in detail. For 3, 4a, and 5 a series of reversible one-electron-transfer waves leads to the formation of the anions and cations [M(L)(2)](2-),(1-),(1+),(2+) which have been characterized spectroelectrochemically. All redox processes are shown to be ligand-based.

The hexavalent state, considered to be the highest oxidation level accessible for iron, has previously been found only in the tetrahedral ferrate dianion, FeO4(2-). We report the photochemical synthesis of another Fe(VI) compound, an octahedrally coordinated dication bearing a terminal nitrido ligand. Mössbauer and x-ray absorption spectra, supported by density functional theory, are consistent with the octahedral structure having an FeN triple bond of 1.57 angstroms and a singlet d2(xy) ground electronic configuration. The compound is stable at 77 kelvin and yields a high-spin Fe(III) species upon warming.

Two series of square planar, diamagnetic, neutral complexes of nickel(II), palladium(II), and platinum(II) containing two N,N-coordinated o-diiminobenzosemiquinonate(1-) pi radical ligands have been synthesized and characterized by UV-vis and (1)H NMR spectroscopy: [M(II)((2)L(ISQ))(2)], M = Ni (1), Pd (2), Pt (3), and [M(II)((3)L(ISQ))(2)] M = Ni (4), Pd (5), Pt (6). H(2)[(2)L(PDI)] represents 3,5-di-tert-butyl-o-phenylenediamine and H(2)[(3)L(PDI)] is N-phenyl-o-phenylenediamine; (L(ISQ))(1-) is the o-diiminobenzosemiquinonate pi radical anion, and (L(IBQ))(0) is the o-diiminobenzoquinone form of these ligands. The structures of complexes 1, 4, 5, and 6 have been (re)determined by X-ray crystallography at 100 K. Cyclic voltammetry established that the complete electron-transfer series consisting of a dianion, monoanion, neutral complex, a mono- and a dication exists: [M(L)(2)](z)z = -2, -1, 0, 1+, 2+. Each species has been electrochemically generated in solution and their X-band EPR and UV-vis spectra have been recorded. The oxidations and reductions are invariably ligand centered. Two o-diiminobenzoquinones(0) and two fully reduced o-diiminocatecholate(2-) ligands are present in the dication and dianion, respectively, whereas the monocations and monoanions are delocalized mixed valent class III species [M(II)(L(ISQ))(L(IBQ))](+) and [M(II)(L(ISQ))(L(PDI))](-), respectively. One-electron oxidations of 1 and trans-6 yield the diamagnetic dications [cis-[Ni(II)((2)L(ISQ))((2)L(IBQ))](2)]Cl(2) (7) and [trans-[Pt(II)((3)L(ISQ))((3)L(IBQ))](2)](CF(3)SO(3))(2) (8), respectively, which have been characterized by X-ray crystallography; both complexes possess a weak M.M bond and the ligands adopt an eclipsed configuration due to weak bonding interactions via pi stacking.