p-Hydroquinone–metal compounds: synthesis and crystal structure of two novel V^V–p-hydroquinonate and V^IV–p-semiquinonate species

Abstract

Reaction of the p-hydroquinone derivative H2Na4bicah.4H2O with either VIVOSO(4).3H2O and NaVVO3 in equivalent quantities or with NaVVo3 yields the tetranuclear VIVO2+ macrocycle-semiquinonate compound Na6[(VIVO)4-(mu2-O)2[mu2-bicas.(-5)-N,O,O,O]2].Na2SO(4).20H2O (1.Na2SO(4).20H2O) and the dinuclear cis-VVO2(+)-hydroquinone species Na4[(VVO2)2[mu2-bicah(-6)-N,O,O,O]].11H2O (2.11H2O) respectively. Compounds 1.Na2SO(4).20H2O and 2.11H2O were characterized by X-ray structure analysis and ab initio calculations.

σ-Bonded p-Dioxolene Transition Metal Complexes

“…The first hydroquinone complex characterized by crystallography has been reported 30 years ago (Heistand, et al, 1982). However only the last 10 years the number of the characterized by crystallography p-dioxolene complexes has increased significantly, including the first p-semiquinone complex in 2002 (Drouza, et al, 2002). This is in marked contrast to the extensive structural chemistry of chelate stabilized o-dioxolene metal complexes reported in the literature (Pierpont, 2001).…”

A journey into the electrochemistry of vanadium compounds

“…Actually, we found only one example of this type of ligands (Chart 5), that gave a tetranuclear VO 2+ complex, a macrocyclesemiquinonate compound, with two oxygen atoms bridging VO moieties two by two [98]. Cyclic voltammetry, rotating disk voltammetry and coulometry gave a reversible and a quasireversible one-electron metal centered redox processes, at 0.48 V vs. NHE for the V(IV) 4 → V(IV) 3 ,V(V) oxidation and 0.10 V for the V(IV) 4 → V(IV) 3 ,V(III) reduction, respectively.…”

NMR characterization and dynamics of vanadium(V) complexes with tripod (hydroquinonate/phenolate) iminodiacetate ligands in aqueous solution

“…At pH below 7, the complexes are reduced, giving green and at pH below 6 dark blue solutions originated from vanadium(IV)/semiquinonate [17,18] and from vanadium(IV/V) oxygen-bridged complexes [16]. Above pH 8.5, the complexes partially hydrolyze (less than 5 % at pH 8.5) to form vanadate, vanadate oligomers, and free ligand.…”

“…The spectroscopic properties of 1 (IR, UV-vis, and NMR spectroscopies) are exactly the same with those of the complex Na 4 2 O that has been previously reported by us [18], revealing that the anions of both the Na + and NH 4 + salts are identical in solid state and in solution. Figure 1 shows the structure and the labeling of the dinuclear anion, which has been obtained from the X-ray crystal structure of Na 4 The infrared spectra of 1-3 show two bands, one symmetric and one antisymmetric at 889, 868 for 1, 945, 907 for 2, and 916, 880 cm -1 for 3 attributed to the V=O bonds of VO 2 + .…”

“…In order to stabilize the coordination of phenolate oxygen to the metal, we have synthesized new tripod phenolate/hydroquinonate ligands substituted with iminodiacetic group at o-position [15][16][17][18]. The iminodiacetate arms have been employed to mimic the protein environment in enzyme active sites around tyrosine.…”