Nickel clusters electronic properties

Physics of Nickel Clusters. 2. Electronic Structure and Magnetic Properties. 

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.

This result emphasizes the role of interstitial atoms in determining the electronic structure and the properties of these materials. The NigCe core of the cluster can be regarded as a microscopic fragment of a nickel carbide. The interstitial main group atoms form strong bonds with the surroundings these bonds may be viewed as initial step in the formation of a different phase (carbides, nitrides, etc.) within the cluster complex. 

The glass-coloring experiments have been performed with gold, silver, nickel and other metals, which are much more difficult to handle theoretically than the alkalis. Among the latter, sodium is the best representative of the nearly free electron gas or jellium model which forms the basic assumption of some of the articles found here. Therefore this review is restricted to sodium clusters, and more specifically to their optical and thermal properties. 

MICHEAU - My comments deals with azeotropic binary mixtures. We have recently made some experimental measurements of the thermodynamic parameters of a thermochronic equilibrium in azeotropic liquid mixtures. Our thermochronic equilibrium (Nickel complexes NiR + 2S N1R2S2) is sensitive to the donor number of the solvent S which is an empirical measure of the availability of the electronic doublet of S. What we have found in azeotropic mixtures (alcohol + halogenated hydrocarbons) is that near the room temperature there is a kind of natural compensation of the alcohol doublet availability by the presence of halogenated hydrocarbons molecules this compensation shifts the equilibrium position near 50/50 (solvated vs non solvated complex). This property is spontaneous with the azeotropes we have studied, but must to be adjusted accurately by varying the molar ratio with similar binary mixtures not giving azeotropes. So, it appears that azeotropes exhibit from this point of view some singular propertie. My question is Do you have or do you know some results about reactivity studies in azeotropic mixtures Could an azeotrope be considered as a model of a particular supermolecule or cluster ... 

---