A series of four-coordinate square-planar nickel(II) complexes of o-phenylenebis(N'-methyloxamidate)(L1) and related o-phenylene(N'-methyloxamidate)oxamate (L2) and o-phenylenebis(oxamate)(L3) tetradentate ligands have been synthesized and characterized structurally, spectroscopically and electrochemically. The parent nickel(II)-L1 complex presents an intense MLCT band in the UV region (lambda max = 357 nm) and a distinctive 1 s --> 4p CT satellite in the Ni K-edge XANES spectrum (E = 8339.2 eV). These features together with the short Ni-N(amidate) bond lengths (1.85-1.93 A) as revealed by the analysis of the Ni K-edge EXAFS spectrum and confirmed by single-crystal X-ray diffraction are typical of square-planar low spin (S = 0) Ni(II) ions. The dianionic nickel(II) complexes, [Ni(II)L(i)](2-)(i = -3), experience two redox processes in acetonitrile at 25 degrees C. The first redox process, at moderately low potentials (E1 = 0.12-0.52 V vs. SCE), is a reversible one-electron metal-centered oxidation to the corresponding monoanionic nickel(III) complexes, [Ni(III)L(i)]-. The second redox process, at relatively high potentials (E2 = 0.86-1.04 V vs. SCE), is a quasireversible to irreversible one-electron oxidation largely centered on the o-benzenediamidate fragment of the non-innocent ligand, yielding the corresponding neutral nickel(iii) complexes with a o-benzosemiquinonediimine pi-cation radical ligand, [Ni(III)(L(i))*+]. The singly and doubly oxidized species of the parent nickel(II)-L1 complex have been prepared by chemical oxidation and characterized spectroscopically in acetonitrile at -40 degrees C. The stable singly oxidized nickel(III)-L1 species presents an intense LMCT band in the NIR region (lambda max = 910 nm) and a rhombic X-band EPR spectrum (g1 = 2.193, g2 = 2.080 and g3 = 2.006) characteristic of square-planar low spin (S = 1/2) Ni(III) ions. The unstable double oxidized nickel(III)-L1 pi-cation radical species exhibits a rather intense visible band (lambda max = 645 nm) that is tentatively assigned as a MLCT transition from the Ni(III)-benzosemiquinone type ground state to the Ni(IV) excited state.
The title compound, [Cu2Cl4(C20H18N2O)2], is a centrosymmetric dimer bridged through the Cl atoms. The bridging Cu2Cl2 unit is planar and each CuII ion has two different distances to the bridging Cl atom. The CuII ions are coordinated to three Cl and two N atoms in a square‐pyramidal disposition. Hydrogen bonds are formed by –OH and –NH with the Cl atoms.
The title compounds, C20H16ClNO and C21H19NO2, adopt syn orientations of the C=O and N-H bonds but, like their analogues, form no strong intermolecular hydrogen bonds.
The title compound, [Cu2Cl4(C20H17ClN2O)2], is a centrosymmetric dimer bridged through the Cl atoms. The bridging Cu2Cl2 unit is planar and the geometry around the CuII ions is that of a square pyramid.
The title compound, [Cu2Cl4(C42H40N4O2)], is a binuclear molecule bridged by two Cl atoms. The bridging unit Cu2Cl2 is almost planar and the CuII ions are coordinated by two N and three Cl atoms forming a square pyramid. There are two bifurcated hydrogen bonds.
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