Solvation nickel

Several hydrido(phenoxo) complexes of nickel, trans-[NiH(OPh)L2] (6) (a L= P Prs b L = PCys c L = PBnj), have been prepared by the metathesis reaction of NaOPh with trans-[NiHClL2] (Eq. 6.6). The complex 6c was obtained as the phenol-solvated complex whose structure was determined by X-ray analysis [9]. An analogous platinum complex trans-[PtH(OPh)(PEt3)2] (7) was prepared by the reaction of trans-[PtH(N03)(PEt3)2] with NaOPh (Eq. 6.7). The complex 7 is air-stable but thermally sensitive and decomposes at room temperature. The structure was elucidated by X-ray analysis [10]. 

Tri-ethylene diamine nickel hydroxide [Ni(en)3](OH)2 Nioxen Good solvating properties, extensive oxidative degradation, coloured (violet)... 

The acceptor properties of Ni2 + are weaker than those of Co2 + and under analogous conditions the extent of complex formation is smaller. When sodium azide is added to a 10 3 molar nickel (II) perchlorate solution in excess, the only azide-complex is monoazidonickel (II). The monochloro complex is present only in strong hydrochloric acid 81L Due to the low solvating properties of DMA even tetrachloronickelate (II) is found in such solutions. 

As we have seen, an area of major importance and of considerable interest is that of substitution reactions of metal complexes in aqueous, nonaqueous and organized assemblies (particularly micellar systems). The accumulation of a great deal of data on substitution in nickel(II) and cobalt(II) in solution (9) has failed to shake the dissociative mechanism for substitution and for these the statement "The mechanisms of formation reactions of solvated metal cations have also been settled, the majority taking place by the Eigen-Wilkins interchange mechanism or by understandable variants of it" (10) seems appropriate. Required, however, are more data for substitution in the other... 

In the first instance (1,3) two types of nickel are used on the side exposed to the gas, large pores are produced in the metal and adjacent to this structure, a network of smaller pores are produced to hold back the electrolyte. The reacting gases diffuse rapidly in the large pores and come in intimate contact with the electrolyte present in the small pores. For the electrochemical reaction po occur, a three phases contact is needed since a gaseous reactant produces a solvated reactior oro uct nd in this process an electron is given or withdrawn from a solid conducting substrate. 

The Birch reduction of dibenzofuran is reported to give 1,4-dihydro-dibenzofuran. The electrochemical reduction of dibenzofuran by solvated electrons is reported to produce a dihydrodibenzofuran and a tetrahydro-dibenzofuran, both of unspecified structure. Treatment of dibenzofuran with W-7 Raney nickel in boiling methanol gave a moderate yield of trans-2-phenylcyclohexanol, whereas treatment of dibenzofuran with Raney nickel alloy and aqueous sodium hydroxide gave a low yield of 2-biphenylol. ... 

Generally, smaller particles are obtained with polar, more highly solvating solvents. However, these solvents do not necessarily yield the most active metal slurries. The reactivities vary, and the metal slurries can be fine tuned somewhat for use in specific types of reactions. For example, nickel particles from pentane are very active as hydrogenation catalysts, whereas nickel particles from THF are not active as hydrogenation catalysts but are very active in alkyl halide reactions. 

Whatever the precursor, the formation of an intermediate solid phase was always observed. It can be inferred from X-ray diffraction (Fig. 9.2.7) and infrared spectroscopy that this intermediate phase shows a lamellar, incompletely ordered structure (turbostratic structure) built up with parallel and equidistant sheets like those involved in the lamellar structure of the well-crystallized hydroxides Ni(OH)2 or Co(OH)2, these sheets are disoriented with intercalation of polyol molecules and partial substitution of hydroxide ions by alkoxy ions (29). The dissolution of this solid phase, which acts as a reservoir for the M(I1) solvated species, controls the concentration of these species and then plays a significant role in the control of the nucleation of the metal particles and therefore of their final morphological characteristics. For instance, starting from cobalt or nickel hydroxide as precursor in ethylene glycol, the reaction proceeds according to the following scheme (8) ... 

Axial perturbation may be taken to indicate the presence of negative charge on the 2-axis, which means that there must be atoms there. From the chemist s point of view it is interesting to know what sort of atoms lie on the axis, and whether they should be regarded as coordinated to the metal or not. Maki (161) proposed that, in solutions of these nickel chelates, all molecules are equally solvated, and that the difference between pyridine and inert solvents is only one of degree. In the melts there must then be some sort of molecular interaction, which does not have more than a minimal effect on the viscosity (222) the melts can be regarded as auto-solutions (221). 

When the apparently penta-coordinated diarsine complexes just described are dissolved in solvents more polar than nitrobenzene, they tend to dissociate into halide ions and bivalent cations, thus becoming 2 1 electrolytes (119). The effect is most marked with the platinum compounds. It has been shown that solvation effects might be less with platinum than with palladium, and so, other things in the equilibria being equal, it can also be concluded that the bonding of further ligands by a square-planar complex is much weaker with platinum than with palladium. Square-planar nickel complexes are of course the most ready to take up further ligands. 

CjHjS, Thiophene, tetrahydro-gold complexes, 26 85-87 C4H,NO, 2-Propenamide, 2-methyl-nickel complex, 26 205 C4H1()02, Ethane, 1,2-dimethoxy-solvates of chromium, molybdenum, and tungsten carbonyl cyclopentadienyl complexes, 6 343 tungsten complex, 26 50 ytterbium complex, 26 22 C4H i02.NaC5H5, Ethane, 1,2-dimethoxy-compd. with cyclopentadienylsodium, 26 341... 

Nickel(II) complexes with the ligands (76b) and (76d) have been reduced in aqueous solution by solvated electrons with the aid of the pulse radiolysis technique.314 The decay kinetics and the behaviour of these complexes as bases and as reducing agents have also been studied. 

Bis(salicylaldoximato)nickel(II) is diamagnetic in the solid state, but becomes partially paramagnetic in solution in chloroform157 and aqueous dioxane.151 This is likely to be due to molecular association or solvation,158 rather than to the adoption of a distorted tetrahedral structure in solution.151 The nickel(II) complex readily forms pseudo-octahedral bis-adducts in the presence of large amounts of amines,159 160 although analogous complexes of commercial orffto-hydroxy-oximes have been reported to retain the square-planar structure in hydrocarbon solution in the presence of moderate amounts of ammonia or aliphatic amines.161... 

The use of solvating extractants in the recovery of gold and platinum-group metals (PGM) was described in the previous section. These extractants have also found some specialized applications in the extractive metallurgy of base metals. For example, they have been used in the recovery of uranium, the separation of zirconium and hafnium, the separation of niobium and tantalum, the removal of iron from solutions of cobalt and nickel chlorides, and in the separation of the rare-earth metals from one another. 

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