Ni II oxide

Bunsenite (NiO) is extremely rare, and a member of the periclase group of minerals. It had been discovered as early as 1868 in Johanngeorgenstadt, Erzgebirge, Saxony, Germany in a hydrothermal Ni-U vein. It is translucent to opaque, and occurs as well-formed fine sized crystals (up to 3 mm). Its hardness is 5.5, the colour pistachio-green, the lustre adamantine, and the streak brownish black. 

The lattice of NiO is face centred cubic, space group Fm3m, with imit cell dimensions ao = 4.177 A, Z = 4, / (calc.) = 6.806 g cm (according to JCPDS-ICDD card No.4-835, [53SWA/TAT]), /)(obs.) = 6.4 - 6.8 g-cm l 

A very accurate technique for the determination of the standard entropy S (298.15 K) of a solid crystalline compound is the integration of low-temperature heat capacity data,, between 0 and 298.15 K  

The uncertainty has been chosen, such that both values (the result of the present evaluation and the value of King [57KIN]) fall within the error limits. 

The heat content of nickel oxide was investigated at temperatures above 

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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.

The oxidative addition of aryl halides to Ni(0) affords trans-arylNi(II) halides and paramagnetic Ni(I) halides. An overall second-order rate-determining step (rate = K2[Ni(0)][ArX]) involves electron transfer from Ni to aryl halide, perhaps by way of a complex . A paramagnetic ion pair is the common intermediate which is partitioned into the Ni(II) oxidation adduct and the Ni(I) adduct ... 

The [Agg] cation, interspersed with Ag+, is also found in the structures of Ag(0,I) compounds such as AgjSi04 [152], AggGe04 [153], and AggPb20g [154]. Startlingly, the metallic conductivity and antiferro magnetic behavior of Ag2Ni02, ostensibly an Ag(I)/Ni(II) oxide, are consistent with its formulation as a mixed-valent Ag(0,I) complex, [Ag2]" [Ni Oj]" [155]. 

NiL]2[NiL]" [l3T], where L = tetrabenzoporphyrinate. The conductivity is interpreted in terms of the Ni(III) and Ni(II) oxidation states in the NiNiNi... chains, together with rapid interconversion between metal-oxidized and ligand-oxidized forms [Ni(III)L] and [Ni(II)(L )] , respectively/... 

Polarographic recording made it possible to obtain data on the dissolution rates of dispersed particles of Cu(Il), Fe(III) and Ni(II) oxide phases and some other elements. Quantitative analysis of solutions of Al(III) and Mo(VI) oxides was made by spectrophotometric methods allowing determination of A1 and Mo. Dissolution rates for series of samples were examined in dependence on their crystal or amorphous structure as well as on the real micro- and macrostructure linear sizes of the particles, characteristics of the pore structure and specific surface area. 

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