Nickel II

Nickel(II) is one of the least reactive of the labile metal ions and the most amenable as regards kinetic investigation. Indeed, more than a hundred complex formations have been studied. Although some complexes require fast reaction techniques like temperature-jump relaxation, many systems have been studied adequately by more normal flow methods. The mechanisms of ligand replacement in Ni(II) complexes have been reviewed a number of times, notably by Wilkins [77]. 

The rates of formation of Ni(II) complexes with selected monodentate ligands are given in Table 6. The following Eigen-type mechanism (also described as Sn 1 IP [78], or Ij [79]) 

Rate coefficients for formation of nickel(II) complexes with monodentate ligands in aqueous solution at 25°C [77 ] 

Bidentate ligands complex with nickel(ll) by the following extension of the basic mechanism where L—L is the ligand, (HjOjsNi—L—L is the inner-sphere complex with one end of the ligand unattached, and NiLj is the chelate product. 

Application of the steady-state assumption to the concentrations of the intermediates produces [89] 

The formation of nickel dimethylglyoximate complex may be expressed as follows  

Materials Required Ammonium nickel sulphate (pine) 0.135 g citric acid 5.0 g dilute ammonia solution dimethylglyoxime solution (dissolve 0.50 g of dimethyl-glyoxime in 250 ml of ammonia solution and diluting to 500 ml with water) 20 ml chloroform 50 ml  

Theory Dithizone and 1, 10-phenanthroline (see Section 27.3.3) help in the synergistic extraction of Ni (II) both quantitatively and rapidly over a wide range of pH between 5.5 to 11.0 to give rise to a dark coloured mixed-ligand complex that absorbs at 520 nm. The resulting complex bears the following vital characteristic features, namely  

Materials Required Ammonium nickel sulphate (pure) 0.0135 g phthalate or acetate (ethanoate) buffer (pH 6.0) 5 ml dilute ammonia solution chloroform 15 ml sodium hydroxide (0.1 M) 10.0 ml  

Caution All glassware must be rinsed with dilute acid and then thoroughly with distilled water. 

This is a somewhat surprising result given nickelate phases are known to form, for example, Na2Ni02. 

The ionic radius of nickel(ll) has been shown by Shannon (1976) to be 0.69 A. 

Some studies selected a stability constant for Ni(OH)3 (Tremaine and LeBlanc, 1980b Ziemniak et al, 1989) from solubility studies across a wide temperature range. However, more recent studies (Ziemniak and Goyette, 2004 Palmer and Gamsjager, 2010 Palmer et al, 2011) found no evidence for formation of this species. This review concurs with this latter view and no stability constant is selected for Ni(OH)3 . 

Temperature Dependence The solubility data accepted for bunsenite (NiO(s)), 

The solubility constant is consistent with that selected by Gamsjager et al. (2005) (log lCgj o = 12.48 0.15) however, more recent data are more negative than this value. From the temperature dependence of the solubility constants, the enthalpy of reaction at 25 C is 

Nickel(n).—Complexes. A detailed examination of the cr stal field description of tetragonal nickel(ii) complexes revealed the possible existence of and 

The reactions (M = Ni, Pd, or Pt) were followed by determining the changes in epr spectra of the Cu(II) species. The fact that the exchange is inhibited by free ligand and accelerated by solvated Cu(II) ions is not in accord with the mechanism proposed earlier for this type of reaction. It is suggested that a chain mechanism operates but that the chain carriers are the monoligand complexes [Cu(S—S) and M(S —S )] rather than the free ligands. Two papers by 

Relative second-order rate constants (25°C, x = 0.1 A/ in acetone) 1 1900 9 X 10  

Cusumano report reactions of square-planar Ni(II) chelates with bipy and other bidentate heterocyclic amines. In the first rate constants were measured for the forward and reverse reactions  

Values of A5, AfT and A5° are given and a value of less than unity for the gradient of the free energy relationship [log(rate constant) as ordinate versus log(equilibrium constant)] implies an mechanism. The planar complexes [NiX2L2] (X = Cl, Br, I, or NCS L = pyridine derivative with methyl groups in the 2-and 6-position) are uniquely inert to substitution and are not even attacked by strong mineral acids.This lack of reactivity is attributed to steric hindrance. 

relaxation study of fluoride complexes of the transition metals gives the expected result that nickel(ii) complexes are less labile than those 

Rates and activation parameters have been determined for acid aquation of [Ni4(OH)4] +, which exists under certain conditions in aqueous alkaline solutions of nickel(ii). The activation enthalpy is comparable with that for hydroxo-bridge breaking in [Cr2(OH)2] the activation entropy is consistent with breakdown of a polymeric structure.  

Stereochemistry is important in controlling the reactivity of copper(ii) complexes of tet-a, tet-b, and trans- A-d a [formulae (7), (7), (8)]. Strongly acidic conditions are required for aquation of complexes of these fairly inflexible ligands. A more widely ranging study led to the determination of kinetic parameters for aquation of zinc(ii), cadmium(ii), copper(ii), nickel(ii), and cobalt(ii) complexes of some bi-, tri-, and quadri-dentate macrocyclic ligands, e.g. bis-pyridylisoindole (18)T  

The water-insoluble, green NiO is obtained by thermal decomposition of NiC03 or Ni(N03)2 and crystallizes with the NaCl structure thin amorphous films of NiO exhibiting electrochromic behaviour (see Box 22.4) may be deposited by CVD (chemical vapour deposition, see Section 27.6) starting from [Ni(acac)2]. Nickel(II) oxide is antiferromagnetic 

A range of coordination geometries is observed for nickel(II) complexes with coordination numbers from 4 to 6 being common octahedral and square planar geometries are most usual. Examples include  

Some structures are complicated by interconversions between square planar and tetrahedral, or square planar and octahedral coordination as we discuss later. In addition, the potential of some ligands to bridge between metal centres may cause ambiguity. For example, alkali metal salts of [NiF3] , [NiF4] and [NiCl3] crystallize with extended 

Magnetic moments of octahedral Ni(II) complexes are usually close to the spin-only value of 2.83 b- In contrast, tetrahedral complexes possess magnetic moments 4 b due to orbital contributions (see Section 20.8), and square 

For some Ni(II) complexes, there is only a small energy difference between structure types. In Section 19.7, we stated that both trigonal bipyramidal and square-based pyramidal [Ni(CN)5] ions (equation 21.90) are present in crystals of [Cr(en)3][Ni(CN)5]1.5H20. In the anhydrous salt, however, the anions are square-based pyramidal. It is impossible to give a simple interpretation of these observations which may be attributed to a subtle balance of steric and electronic effects . 

Vj Fig. 22.27 (a) Representation of part of a layer of corner-sharing NiF octahedra in K2Nip4. (b) The structure of [ Ni(acac)2 3] (X-ray diffraction) with H atoms omitted [G.J. Bullen et al. (1965) Inorg. Chem., vol. 4, p. 456], Colour code Ni, green C, grey O, red. 

In Section 21.10, we noted that [Co(acac)2] is tetrameric. Similarly, [Ni(acac)2] oligomerizes, forming trimers (Fig. 21.29b) in which [acac] ligands are in chelating and bridging modes. Reaction of [ Ni(acac)2 3] with 

hydrated nickel(II) salts and their aqueous solutions usually contain green [Ni(OH2)6l, the electronic absorption spectmm of which was shown in Fig. 20.21 with that of [Ni(NH3)g]. Salts of the latter are typically blue, giving violet solutimis. In aqueous solution, [Ni(NH3)g] is stable only in the presence of excess NH3 without which species such as [Ni(NH3)4(OH2)2] form. The violet chloride, bromide or perchlorate salts of [Ni(en)3] are obtained as racemates, the catimi being kinetically labile (see Section 26.2). The octahedral complexes trans-[Ni(C104-0,0 )2(NCMe)2] (21.52) and frans-[Ni(C104- )2(py)4] illustrate the ability of perchlorate ions to act as bidentate or monodentate ligands respectively. The latter complex is discussed again later. 

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Aqueous ammonia can also behave as a weak base giving hydroxide ions in solution. However, addition of aqueous ammonia to a solution of a cation which normally forms an insoluble hydroxide may not always precipitate the latter, because (a) the ammonia may form a complex ammine with the cation and (b) because the concentration of hydroxide ions available in aqueous ammonia may be insufficient to exceed the solubility product of the cation hydroxide. Effects (a) and (b) may operate simultaneously. The hydroxyl ion concentration of aqueous ammonia can be further reduced by the addition of ammonium chloride hence this mixture can be used to precipitate the hydroxides of, for example, aluminium and chrom-ium(III) but not nickel(II) or cobalt(II). 

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. 

These are practically insoluble in water, are not hydrolysed and so may be prepared by addition of a sufficient concentration of sulphide ion to exceed the solubility product of the particular sulphide. Some sulphides, for example those of lead(II), copper(II) and silver(I), have low solubility products and are precipitated by the small concentration of sulphide ions produced by passing hydrogen sulphide through an acid solution of the metal salts others for example those of zincfll), iron(II), nickel(II) and cobalt(II) are only precipitated when sulphide ions are available in reasonable concentrations, as they are when hydrogen sulphide is passed into an alkaline solution. 

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. 

Addition of an alkali metal hydroxide solution to an aqueous solution of a nickel(II) salt precipitates a finely-divided green powder. nickel(II) hydroxide NilOHfj on heating this gives the black oxide. NiO. which is also obtained by heating nickel(II) carbonate or the hydrated nitrate. Black nickel(II) sulphide, NiS, is obtained by passing hydrogen sulphide into a solution of a nickel(II) salt. 

If nickel(II) cyanide, Ni(CN)2, is dissolved in excess potassium cyanide, the orange-red complex salt K2Ni(CN)4. HjO can be crystallised out this contains the stable square-planar [Ni(CN)4] anion. 

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. 

Nickel (II) Catalyzed Cross-Coupling with Grignard Reagents (Kumada Reaction) Pure AppJ. Chem. 1980, 52, 669 Bull Chern. Soc.Jpn. 1976, 49, 1958... 

In the previous section efficient catalysis of the Diels-Alder reaction by copper(II)nitrate was encountered. Likewise, other bivalent metal ions that share the same row in the periodic system show catalytic activity. The effects of cobalt(II)nitrate, nickel(II)nitrate, copper(II)nitrate and zinc(ll)nitrate... 

An equilibrium constant for binding of 3.8c to the nickel(II)(L-tryptophan) complex of 805 M has been obtained, compared to 530 M in the presence of glycine... 

Fortunately, in the presence of excess copper(II)nitrate, the elimination reaction is an order of magnitude slower than the desired Diels-Alder reaction with cyclopentadiene, so that upon addition of an excess of cyclopentadiene and copper(II)nitrate, 4.51 is converted smoothly into copper complex 4.53. Removal of the copper ions by treatment with an aqueous EDTA solution afforded in 71% yield crude Diels-Alder adduct 4.54. Catalysis of the Diels-Alder reaction by nickel(II)nitrate is also... 

The resulting macrocyclic ligand was then metallated with nickel(II) acetate. Hydride abstraction by the strongly electrophilic trityl cation and proton elimination resulted in the formation of carbon-carbon double bonds (T.J. Truex, 1972). 

Nickel Carbonyl The extremely toxic gas nickel carbonyl can be detected at 0.01 ppb by measuring its chemiluminescent reaction with ozone in the presence of carbon monoxide. The reaction produces excited nickel(II) oxide by a chain process which generates many photons from each pollutant molecule to permit high sensitivity (315). 

Nickel sulfide, NiS, can be prepared by the fusion of nickel powder with molten sulfur or by precipitation usiag hydrogen sulfide treatment of a buffered solution of a nickel(II) salt. The behavior of nickel sulfides ia the pure state and ia mixtures with other sulfides is of iaterest ia the recovery of nickel from ores, ia the high temperature sulfide corrosion of nickel alloys, and ia the behavior of nickel-containing catalysts. 

Yields were improved to >37% by the addition of sodium sulfite to the reaction mixture. Apart from the sulfite, the C -component unit has the greatest influence on the yield of foHc acid. The use of nickel(II) chloride as an additive has been claimed to give higher yields (25). 

Eig. 7. CycHc voltammograms for the reduction of 1.0 mAf [2,2 -ethylene-bis(nitrilomethyHdyne)diphenolato]nickel(II) in dimethyl formamide at a glassy carbon electrode, in A, the absence, and B and C the presence of 2.0 and 5.0 mAf 6-iodo-l-phenyl-l-hexyne, respectively (14). 

In the presence of 6-iodo-l-phenyl-l-hexyne, the current increases in the cathodic (negative potential going) direction because the hexyne catalyticaHy regenerates the nickel(II) complex. The absence of the nickel(I) complex precludes an anodic wave upon reversal of the sweep direction there is nothing to reduce. If the catalytic process were slow enough it would be possible to recover the anodic wave by increasing the sweep rate to a value so fast that the reduced species (the nickel(I) complex) would be reoxidized before it could react with the hexyne. A quantitative treatment of the data, collected at several sweep rates, could then be used to calculate the rate constant for the catalytic reaction at the electrode surface. Such rate constants may be substantially different from those measured in the bulk of the solution. The chemical and electrochemical reactions involved are... 

Pyridazines form complexes with iodine, iodine monochloride, bromine, nickel(II) ethyl xanthate, iron carbonyls, iron carbonyl and triphenylphosphine, boron trihalides, silver salts, mercury(I) salts, iridium and ruthenium salts, chromium carbonyl and transition metals, and pentammine complexes of osmium(II) and osmium(III) (79ACS(A)125). Pyridazine N- oxide and its methyl and phenyl substituted derivatives form copper complexes (78TL1979). 

Pyrazole does not react with iodine although pyrazolylsilver is converted into 4-iodopyrazole. 3-Iodoindazole can be obtained by the reaction of iodine with the silver salt of indazole. Kinetic studies on pyrazole iodination have been carried out by Vaughan et al. (71PMH(4)55, B-76MI40402). Coordination of pyrazole by nickel(II) in aqueous solution increases the rate of iodination by factors of two at pH 6 and eight at pH 7.2 (72JA2460). 

Bis-(triphenylpbospbine)nickel(II) chloride [14264-16-5] M 654.2, m 225 (dec). Wash with glacial AcOH and dry in vac over H2SO4 and KOH until AcOH is removed. [J Chem Soc 719 1958.]... 

Nickel (II) acetate (4H2O) [6018-89-9] M 248.9, d 1.744, pK / 8.94 (from Ni + hydrolysis). Recryst from aqueous AcOH as the green tetrahydrate. Soluble in 6 parts of H2O. It forms lower hydrates and should be kept in a well closed container. [ZAnorg Allg Chem 343 92 1966.]... 

Nickelocene [bis-(cyclopentadienyl)nickel II] [1271-28-9] M 188.9, m 173-174 (under N2). Dissolve in Et20, filter and evaporate in a vacuum. Purify rapidly by recrystn from pet ether using a solid C02-Me2C0 bath, m 171-173°(in an evacuated tube). Also purified by vacuum sublimation. [J Am Chem Soc 76 1970 954 J Inorg Nud Chem 2 95, 110 7956.]... 

Nickel (II) phthalocyanine [14055-02-8] M 571,3, m >300 , Wash well with H2O and boiling EtOH and sublime at high vacuum in a slight stream of C02. A special apparatus is used (see reference) with the phthallocyanine being heated to red heat. The sublimate is made of needles with an extremely bright red lustre. The powder is dull greenish blue in colour. [J Chem Soc 1719 7936.]... 

The use of quenching agents in polymers is a recent development. Of particular interest are the nickel(II) chelates in polypropylene film and fibre and the even newer hindered amines which appear to combine the roles of antioxidant cmd quenching agent. 

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