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Abstract: Reactions of ZnCl2 with tridentate ligands based either on a 2,2′-bipyridine-substituted verdazyl radical (1) or a 2,6-pyridine-linked verdazyl diradical (2) give trigonal bipyramidal complexes 1·ZnCl2 and 2·ZnCl2, respectively in which the Zn–N bonds to the verdazyl nitrogen atoms are considerably longer than the Zn–N (pyridine) bonds. Electronic and EPR spectroscopy and magnetic susceptibility studies indicate that the perturbation of the verdazyl chromophore in the two Zn complexes is small. However, the redox properties of the Zn complexes are substantially different from those of the free ligand. The oxidation and reduction potentials of the verdazyl radical 1 both shift to more positive potentials in 1·ZnCl2. Voltammetry studies of diradical complex 2·ZnCl2 reveal substantial changes: reduction of the two verdazyl moieties in the complex occurs in a stepwise manner, whereas in the free ligand the two verdazyls have nearly identical reduction potentials. Oxidation of 2·ZnCl2 appears to lead to hemilabile behavior, i.e. the verdazyl–Zn bonds are broken reversibly upon oxidation, based on the voltammetric profile and also based on spectroscopic studies of the neutral and oxidized form of this complex. [Copyright &y& Elsevier]

Abstract: 3-Nitroformazans react with bis(1,1,1,5,5,5-hexafluroacetylacetonato)palladium to afford monometallic complexes. The complexes were characterized via X-ray crystallography, cyclic voltammetry, and electronic spectroscopy. The nature of the aryl substituents on the formazan ligands had a profound effect on the structure and spectroscopy of the complexes, with o-substituted aromatic rings twisted with respect to the ligand, while the p-tolyl substituted derivative adopted a planar structure. The complexes undergo irreversible reductions near −1V versus Fc/Fc+. [Copyright &y& Elsevier]

Abstract: The synthesis, structure, and magnetic properties of a dinuclear Co(II) complex of a tridentate verdazyl radical are presented. The reaction of a tetrazane containing a 4,6-bis(2-pyridyl)-pyrimid-2-yl substituent with cobalt chloride hexahydrate in aerated solution leads to in situ oxidation of the tetrazane to a verdazyl radical which is coordinated to Co(II) in a tridentate manner. The second tridentate coordination site of the verdazyl remains vacant. The crystal structure reveals the complex to be dimeric, with the cobalt ions linked by two bridging chlorides. The structure of Co2Cl2 core is highly asymmetric, with two short (2.3317Å) and two long (2.744Å) Co–Cl bonds. There are relatively short intermolecular contacts between coordinated verdazyl radicals in the solid state. Magnetic susceptibility data from 2 to 300K suggest intramolecular ferromagnetic interactions, and modeling of the high-temperature data produced a best fit with J Co–verdazyl of +20cm−1. [Copyright &y& Elsevier]