Nickel halides, anhydrous

Anhydrous nickel chloride, 17 110 Anhydrous nickel fluoride, 17 110 Anhydrous nickel halides, properties of, 17 HOt... 

A number of nickel(II) alkoxyhalides of the types Ni(OMe)X, Ni3(OMe)5X, Ni3(OMe)4X2 (X = halides) and Ni(OMe)Cl MeOH were prepared by reacting either NaOMe or LiOMe with anhydrous nickel halides in methanol.1495 The structures of these complexes which exhibit ferromagnetic behaviour are thought to involve cubane-type clusters. Other complexes with miscellaneous ligands containing the OH function are collected in Table 76. 

The synthesis of nickel organic compounds often requires a source of organic-solvent-soluble anhydrous nickel halide. 

All four nickel halides are known in the anhydrous state. Except for the fluoride, which is best made indirectly, they can be prepared by direct reaction of the elements. All the halides are soluble in water (the fluoride only moderately so), and from aqueous solutions they can be crystallized as the hexahydrates, except for the fluoride which gives NiF2-3H20. Lower hydrates are obtained from these on storage or heating. 

The higher iodides, however, tend to be unstable and decomposition occurs to the lower iodide (PI5 -> PI3). Anhydrous chlorides and bromides of some metals may also be prepared by the action of acetyl (ethanoyl) halide on the hydrated ethanoate (acetate) in benzene, for example cobalt(II) and nickel(II) chlorides ... 

Nickel forms yellow anhydrous halides NiXjlX = F. Cl. Br) and a black iodide Nil2 all these halides are made by direct combination of the elements, and the chloride by reaction of sulphur dichloride oxide with the hydrated salt. All dissolve in water to give green solutions from which the hydrates can be crystallised the solutions contain the ion [NifHjOls], and the chloride crystallises as NiCl2.6H2O, nickel(II) chloride hexahydrate. 

Titanium is almost invariably resistant towards neutral salts, particularly halides, at temperatures up to 100°C, and in respect of the latter environments it is significantly more resistant than stainless steel. In strong solutions of caustic alkalis, on the other hand, titanium tends to form soluble titanates, and it is not as resistant as say, nickel. While at low or moderate concentrations of alkali there is no significant attack, the metal has appreciable solubility in concentrated or molten caustic alkali. Titanium is however resistant to attack by aqueous ammonia at all concentrations and temperatures and to anhydrous ammonia . 

Electrochemical fluorination in anhydrous hydrogen fluoride (Simons process) involves electrolysis of organic compounds (ahphatic hydrocarbons, haloalkanes, acid halides, esters, ethers, amines) at nickel electrodes. It leads mostly to perfluori-nated compounds, but is accompanied to a high extent by cleavage and rearrangement reactions. The mechanism of the formation of carbocations according to Eq. (1) and Scheme 1 is assumed... 

In anhydrous NiX2 (X = halides), the nickel atom is octahedrally coordinated by six halogen atoms. Their relevant properties and synthetic procedures are reported in Table 94.2220,2221... 

Solutions of nickel carbonyl in carbon tetrachloride react with chlorine, bromine, or iodine in similar solution, yielding carbon monoxide and the anhydrous halide.7 Thus ... 

The diethyl ester of phenylphosphonous acid (diethoxyphenyl-phosphine) provides an easy pathway to relatively stable telrakis complexes of zero- and low-valent transition metals.1,2 Anhydrous metal halides serve as the metal source for the complexes, avoiding the necessity of inconvenient starting materials such as nickel carbonyl. The nickel(O) complex is formed by reaction with the phosphonite in ethanol with the addition of sodium tetrahydroborate, relatively stable dihydridoiron(l I) and hydridocobalt(I) complexes are obtained. 

ANHYDROUS NICKEL(II) HALIDES AND THEIR TETRAKIS (ETHANOL) AND 1,2-DIMETHOXYETHANE... 

Perhaps the most clearly defined example involves the macrocyclic complex of Curtis, Ni(CT)X2. The solid, violet, paramagnetic, anhydrous chloride and bromide must be carefully protected from moisture for they readily revert to yellow, diamagnetic dihydrates. The fact that two molecules of water are taken up to produce a diamagnetic nickel(II) ion is especially interesting for displacement of the halide, and coordination by the water molecules would surely produce a violet, paramagnetic species... 

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