Nickel redox properties

Also, the structure of the Ni11 complex (379) with the related ligand dimethyltetrathiomalonate has been determined.997 The geometry at the nickel center is approximately square planar with an inversion center. (379) shows reversible redox properties 998 Oxidation with I2 affords 1,3-bis (methylthio)-1,2-dithiolium triiodide. 

Cammack, R., Patil, D., Aguirre, R. and Hatchikian, E. C. (1982) Redox properties of the ESR-detectable nickel in hydrogenase from Desulfovibrio gigas. FEBS Lett., 142, 289-92. 

Cammack, R. P. D., Hatchikian, E. C. and Eernandez, V. M. (1987) Nickel and iron-sulfur centres in Desulfovibrio gigas hydrogenase ESR spectra, redox properties and interactions. Biochim. Biophys. Acta, 912, 98-109. 

In order to improve the resistance of Ni/Al203-based catalysts to sintering and coke formation, some workers have proposed the use of cerium compounds [36]. Ceria, a stable fluorite-type oxide, has been studied for various reactions due to its redox properties [37]. Zhu and Flytzani-Stephanopoulos [38] studied Ni/ceria catalysts for the POX of methane, finding that the presence of ceria, coupled with a high nickel dispersion, allows more stability and resistance to coke deposition. The synergistic effect of the highly dispersed nickel/ceria system is attributed to the facile transfer of oxygen from ceria to the nickel interface with oxidation of any carbon species produced from methane dissociation on nickel. 

The differences in formal potentials of different metal hexacyanometalates is the basis of tuning the redox properties of PCMs by synthesis of mixed solutions, as far as that is possible due to the ion radii. Examples for a continuous tuning of the hexacyanoferrate redox potential are mixed nickel/iron hexacyanoferrates [30], mixed copper/iron hexacyanoferrates [56], and mixed cadmium/iron hexacyanoferrates [33]. 

The redox properties of the quinone-pyrocatecholate system are shown in Scheme 23. If the species NiL2+, NiL and Nil4 are taken into account, they can be assumed to contain nickel(II) ion and coordinated neutral benzoquinone, mononegative semiquinone and dinegative pyrocatecholate, respectively. 

An extensive study of the redox properties of tetraaza macrocyclic complexes of nickel has been performed by Busch and co-workers.3056,3133,3134 Electrochemical data for selected Nim/Nin couples are reported in Table 117. From an analysis of the EPR spectra it has been found that acetonitrile, as well as other molecules or ions like Cl and S04, can coordinate in axial position to give six-coordinate complexes.3056,3141 The g values are indicative of a dj... 

Ring Conformation, Solution, and Redox Properties of Nickel(II) Derivatives of [14]aneN4... 

Fig. 10. Hypothetical reaction cycle for D. gigas hydrogenase, based on the EPR and redox properties of the nickel (Table II). Only the nickel center and one [4Fe-4S] cluster are shown. Step 1 enzyme, in the activated conformation and Ni(II) oxidation state, causes heterolytic cleavage of H2 to produce a Ni(II) hydride and a proton which might be associated with a ligand to the nickel or another base in the vicinity of the metal site. Step 2 intramolecular electron transfer to the iron-sulfur cluster produces a protonated Ni(I) site (giving the Ni-C signal). An alternative formulation of this species would be Ni(III) - H2. Step 3 reoxidation of the iron-sulfur cluster and release of a proton. Step 4 reoxidation of Ni and release of the other proton.

Zeolites containing 3d transition-metal ions were considered in Beran et al. (109-112). The peculiarities of the donor-acceptor interactions of these cations located within six-membered rings with a zeolite lattice were discussed in terms of atomic charges, bond orders, and orbital energies. The redox properties of the cations, the acid-base properties of zeolites, and the dependence of these characteristics on the Si/Al ratio were discussed as well. The authors noted that the forms containing univalent copper and nickel ions should possess the highest electron-donor ability and consequently the... 

In the reduction with 2,2 -bipyridyl, redox reactions are absent and the limiting stage is the transfer of the 2nd electron, [AEo being —60 to —70 mV. Reduction of the nickel(II) complex with PPhs, ( PrO)3P, PhP(OBu)2, or (PhO)3P is limited by the transfer of the 1st electron and is accompanied by comproportionation (PPh3, AEo= 90 mV) and disproportionation reactions (phosphites, AEq< 0). The redox properties of some transition metal-cinnamonitrile cyclo-phosphazene derivatives, e.g., 107-109 have been stuoied by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in aprotic media. 

Chemical vapor deposition (CVD) was applied to produce homogeneous thin films of pure and doped spinel cobalt oxide with similar morphology on the surface of planar and monolithic supports. The planar substrates were used to investigate the thermal stability and the redox properties of the spinel using temperature-programmed methods monitored by emission-FTIR spectroscopy, while the monolithic substrates were used to test the catalytic performance of the deposited films toward the deep oxidation of methane and to evaluate its durability. The high performance of cobalt oxide to oxidize methane in diluted streams was demonstrated at 500 °C. Furthermore, controlled doping of cobalt oxide layers with suitable cations was demonstrated for nickel as an example, which resulted in substantial increase of electric conductivity. 

Cyclic voltammetry and differential pulse polarography have been used to investigate the redox properties of the di-Ni(II) species in acetonitrile. Effectively, a two-electron step was observed for the complex of 30, whereas that of 29 (n = 2) yielded two clear one-electron steps. This is in accord with the occurrence of an interaction between the nickel sites for the latter system containing the shorter link between the isocyclams. 

Ozette, K., Leduc, P., Palacio, M., Bartoli, J.-R, Barldgia, K. M., Fajer, J., Battioni, R, Mansuy, D. (1997). New metalloporphyrins with extremely altered redox properties Synthesis structure and facile reduction to air-stable it-anion radicals of zinc and nickel P-heptanitroporphyrins, J. Am. Chem. Soc., 119 6442. 

An extensive study of the redox properties of tetraaza macrocyclic complexes of nickel has been performed by Busch and co-workers. Electrochemical data for selected... 

Also 6-ferrocenyl-substituted 2,2 -dipyridyl has been obtained by using the Sn methodology, and redox properties on new cobalt(II) and nickel(II) complexes of this ligand have been elucidated [147]. 

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