Nickel/ions/salts

Because of ammine formation, when ammonia solution is added slowly to a metal ion in solution, the hydroxide may first be precipitated and then redissolve when excess ammonia solution is added this is due to the formation of a complex ammine ion, for example with copper(II) and nickel(II) salts in aqueous solution. 

The reactions of aqueous solutions of nickel(II) salts with hydroxide ions, with excess ammonia, with sulphide ion and with dimethyl-glyoxime (see above) all provide useful tests for nickel(II) ions. 

The use of a nichrome stirrer or a catalytic amount of nickel ion is recommended 1 for such reactions to minimize the accumulation of diazonium xanthate however, the catalytic role of nickel ion has not been explored with other diazonium salts. 

E. Miscellaneous methods. Exchange reactions between the tetracyano-nickelate(II) ion [Ni(CN)4]2 (the potassium salt is readily prepared) and the element to be determined, whereby nickel ions are set free, have a limited application. Thus silver and gold, which themselves cannot be titrated complexometrically, can be determined in this way. 

The procedure involved in the determination of these anions is virtually that discussed in Section 10.58 for the indirect determination of silver. The anion to be determined is precipitated as the silver salt the precipitate is collected and dissolved in a solution of potassium tetracyanonickelate(II) in the presence of an ammonia/ammonium chloride buffer. Nickel ions are liberated and titrated with standard EDTA solution using murexide as indicator ... 

Bulk crystalline radical ion salts and electron donor-electron acceptor charge transfer complexes have been shown to have room temperature d.c. conductivities up to 500 Scm-1 [457, 720, 721]. Tetrathiafiilvalene (TTF), tetraselenoful-valene (TST), and bis-ethyldithiotetrathiafulvalene (BEDT-TTF) have been the most commonly used electron donors, while tetracyano p-quinodimethane (TCNQ) and nickel 4,5-dimercapto-l,3-dithiol-2-thione Ni(dmit)2 have been the most commonly utilized electron acceptors (see Table 8). Metallic behavior in charge transfer complexes is believed to originate in the facile electron movements in the partially filled bands and in the interaction of the electrons with the vibrations of the atomic lattice (phonons). Lowering the temperature causes fewer lattice vibrations and increases the intermolecular orbital overlap and, hence, the conductivity. The good correlation obtained between the position of the maximum of the charge transfer absorption band (proportional to... 

Dark green crystals Contains Ni2+ ions (as in nickel(n) salts)... 

As an example, a sample that contains a mixture of copper(II) and nickel(II) salts can be analyzed by first electrolyzing the sample solution under acidic conditions with platinum electrodes such that the copper is plated onto a platinum gauze electrode. Because the solution is acidic, hydronium ion is reduced before nickel ion and there is no interference. After the electrolysis for copper is completed, the electrolysis solution can be neutralized and made basic with ammonia. Having determined the copper and removed it from the platinum electrode, one can electrolyze the remaining basic electrolysis solution to plate nickel on the platinum electrode. 

The use of metal ions as templates for macrocycle synthesis has an obvious relevance to the understanding of how biological molecules are formed in vivo. The early synthesis of phthalocyanins from phthalonitrile in the presence of metal salts (89) has been followed by the use of Cu(II) salts as templates in the synthesis of copper complexes of etioporphyrin-I (32), tetraethoxycarbonylporphyrin (26), etioporphyrin-II (78), and coproporphyrin-II (81). Metal ions have also been used as templates in the synthesis of corrins, e.g., nickel and cobalt ions in the synthesis of tetradehydrocorrin complexes (64) and nickel ions to hold the two halves of a corrin ring system while cycliza-tion was effected (51), and other biological molecules (67, 76, 77). 

The stable nickel(II) salts are derived from nickel(II) oxide, NiO, which is a green substance. The dissolved nickel(II) salts are green, owing to the colour of the hexaquonickelate(II) complex [Ni(H20)6]2 + in short however, this will be regarded as the simple nickel(II) ion Ni2+. A brownish-black nickel(III) oxide Ni203 also exists, but this dissolves in acids forming nickel(II) ions. With dilute hydrochloric acid this reaction yields chlorine gas ... 

To optimize the use of the amorphous sodium titanate powders as catalyst substrates, it is important to fully characterize the ion-exchange properties of the material. Further, the solution properties of the active metal to be loaded onto the support will be an important parameter in the control of the adsorption process. For example, exposure of sodium titanate to a nickel salt solution does not guarantee that nickel will be loaded onto the sodium titanate, or that the nickel, if loaded, will be dispersed on an atomic level. Sodium titanate only behaves as a cation exchange material under certain pH conditions. The solution pH also influences the hydrolysis and speciation of dissolved nickel ions (3), which can form large polymeric clusters or colloidal particles which are not adsorbed by the sodium titanate via a simple ion-exchange process. 

Nickel is found almost exclusively in the +2 oxidation state in its compounds. Aqueous solutions of nickel(II) salts contain the Ni(H20)62+ ion, which has a characteristic emerald green color. Coordination compounds of nickel(II) will be discussed later in this chapter. Some typical nickel compounds are shown in Table 20.9. 

X-ray crystal structures of both dimers have been determined. The Ni—Ni distance of the mixed-valence dimer (2.514(5) A) is shorter than that of the Ni(II) dimer (2.564(1) A), suggesting stronger direct interaction between the two nickel ions. The crystal structure of [Ni2(CH3CS2)4l] consists of infinite chains of Ni2(CH3CS2)4 I Ni2(CH3CS2)4 — I —, which is similar to that of the Pt analogue. All the Ni atoms are equivalent. Vibrational spectra have been discussed (36). The reaction of nickel salt with dithiophenylacetic acid instead... 

The nickel ion forms two rather stable ammonia complexes. When a small amount of ammonium hydroxide solution is added to a solution of a nickel salt (green in color) a pale green precipitate of nickel hydroxide, Ni(OH), is formed. On addition of more ammonium hydroxide solution this dissolves to give a blue solution, which with still more ammonium hydroxide changes color to light blue-violet. 

Nickel forms only one series of salts, containing the nickelous ion, Ni+. As was mentioned in Chapter 24, iron, cobalt, and nickel are sexivalent in the metals and their alloys. This high metallic valency causes the bonds to be especially strong, and confers valuable properties of strength and hardness on the alloys. 

The hydrated salts of nickel such as nickel sulfate, NiSO GHgO. and nickel chloride, NiCU GHsO, are green in color. Nickelous hy droxide, Ni(OH)2, formed as an apple-green precipitate by addition of alkali to a solution containing nickelous ion. When heated it pro duces the insoluble green substance nickelous oxide, NiO. Nickelous hydroxide is soluble in ammonium hydroxide, forming ammonia com plexes such as Ni(NH3)4(HoO). + + and Ni(NHg)g+ +. ... 

In Section 3.11.1.4 it was pointed out that salts of certain transition metals, lanthanides and actinides promote the hydroalumination reaction. Since such metal salts are introduced into the reaction in their high oxidation states it can be assumed that the metal ions are rapidly reduced to a lower oxidation state and that this state is the active catalyst. For nickel(II) salts, Wilke has shown conclusively that the active agent is a nickel(0)-alkene complex. Analogously, for titanium(IV) salts, such as TiCU, Ti(OR>4 and Cp2TiCl2, it is most likely that a titanium(III) state is involved. The possible role of such metal centers in accelerating hydroalumination will be considered in the next section. 

The reduction of imBT ligand with NaBH4 in methanol led to the formation of a saturated octaazamacrocyclic amBT ligand that forms binuclear complexes with zinc(II) and copper(II) [199] and mononuclear clathrochelates with manganese, iron, cobalt, nickel, and zinc (II) [203] by treatment of the free ligand with the corresponding metal ion salts. 

Salts are compounds composed of a metal ion bonded to a nonmetal ion. Their solutions may have different colors. For example, the salt solutions containing copper ions (Cu2+) are usually blue, and those containing nickel ions (Ni2+) are pale green. If a solution contains iron ions (Fe2+ or Fe3+), it may be green or orange, white cobalt solutions (Co2+) are pink. 

Figure 6. Infrared spectra of ammonium nickel Tutton salt doped with 4% deuterium. Top Absorption spectra. Between 2260 and 2364 cm "1 lie the four N—D stretching bands of the NH3D+ ion, above 2380cm 1 the O—D stretching bands of HOD. Bottom Difference spectra before and after IR laser irradiation at the frequencies as indicated by arrows. (Adapted from Fei et al. [105].)...

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