Nickel atom aggregation

Among the nonnoble metals that can be synthesized by radiation-induced reduction in solution, nickel raises some difficulties because the atom formation and aggregation processes undergo the competition of oxidation reactions of highly reactive transients, such as monovalent Ni ion, Ni atom, and the very first nickel oligomers. Nevertheless, in... 

A recent development of work with metal vapors, which lies between atom chemistry and conventional synthetic chemistry, is the preparation of reactive metal slurries. When a metal vapor is condensed with an inert organic compound, e.g., an alkane or sometimes an ether, and the condensate is allowed to warm to room temperature, the resultant slurry contains metal in a reactive form. It is less reactive than the metal atoms because aggregation of the atoms has occurred and is comparable in reactivity to active forms of metal produced by other methods, e.g., Raney nickel. The catalytic and synthetic potential of these metal slurries is being explored (55, 60). 

Much more research has been carried out with polymers in which the coordinated metal atom is part of the chain backbone. Typically, the metal atoms are copper, nickel, and cobalt. Oxygen atoms or carbon atoms adjacent to the metal atom provide the electrons required for the coordinate bond.30 Polymers of this type are often rather intractable, for a variety of reasons. Specifically, insolubility can be a problem for species with moderate molecular weights. Also, coordination between chains can cause aggregation, and ligand-exchange reactions with small molecules such as solvents can cause chain scission. However, in some favorable cases, the intramolecular coordination is sufficiently strong for the polymer to be processed by the usual techniques such as spinning into fibers or extrusion into films.30... 

The characterization of the latter materials by HRTEM (Fig. 7), EXAFS (Fig. 8), XPRD (Fig. 9) and XANES has unambiguously shown their surface to contain small (0.5-1 nm), highly dispersed and crystalhne Pd and Ni clusters, as bimetallic aggregates, Ni-0 as well as single Pd sites, likely stabilized by interaction with oxygen atoms from the nickel oxide. 

The metal-free and nickel derivatives of hexaoctyl-pyridino[3,4]tribenzoporphyrazine generate conventional face-to-face aggregates in solution they exhibit columnar mesophases and form columnar assemblies on evaporation of solntions. By contrast, the zinc derivative forms alternative edge-to-face complexes such as 36 through axial coordination of one pyridine moiety to the zinc atom of another (Figure 25), a process which inhibits mesophase behavior. ... 

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