Ions—Ni

However, when the reductions were carried out with lithium and a catalytic amount of naphthalene as an electron carrier, far different results were obtained(36-39, 43-48). Using this approach a highly reactive form of finely divided nickel resulted. It should be pointed out that with the electron carrier approach the reductions can be conveniently monitored, for when the reductions are complete the solutions turn green from the buildup of lithium naphthalide. It was determined that 2.2 to 2.3 equivalents of lithium were required to reach complete reduction of Ni(+2) salts. It is also significant to point out that ESCA studies on the nickel powders produced from reductions using 2.0 equivalents of potassium showed considerable amounts of Ni(+2) on the metal surface. In contrast, little Ni(+2) was observed on the surface of the nickel powders generated by reductions using 2.3 equivalents of lithium. While it is only speculation, our interpretation of these results is that the absorption of the Ni(+2) ions on the nickel surface in effect raised the work function of the nickel and rendered it ineffective towards oxidative addition reactions. An alternative explanation is that the Ni(+2) ions were simply adsorbed on the active sites of the nickel surface. 

Surface modification of LDPE film can also be brought about by chemical treatment [118] with an aqueous solution of ammoniacal ammonium persulphate in the presence of Ni+2 ions under variable reaction conditions. The investigation of treated surface showed the presence of polar groups (viz. carbonyl and hydroxyl) in the infrared (IR) spectroscopy, with characteristic bands at 1700, 1622 and 3450 cm-1. It is known that the persulphate ion attacks the double-bond-producing epoxy or diol group. However, the destructive oxidation of saturated hydrocarbons does not occur with persulphate alone, but requires the presence of the nickel (II) ion. The authors have proposed the following mechanism of chemical treatment ... 

The five 3d orbitals of the Ni+2 ion are split in the presence of four donor groups lying at the corners of a square, in much the same way as in the presence of an octahedral ligand field (p. 357), but in this case, the splitting is fourfold (p. 363, Exercise 7). Depending upon the strength of the ligand field, the complex may be either of the spin-free or spin-paired type ... 

The drastic effect of the state of polarization upon the rates of chemical reactions is well known to the analytical chemist. Some metal sulfides—e.g., NiS— cannot be precipitated from an acidified solution but once formed will resist acid attack because the penetration of protons into S 2 ions which are polarized by cations such as Ni+2 ions is a reaction with a high energy barrier. 

The paper presents the experimental and theoretical data regarding the realization and characterization of three liquid-membrane electrodes, which have not been mentioned in the specialized literature so far. The active substances whose solutions in nitrobenzene have constituted the membranes on a graphite rod, are simple complex combinations of the Cu(II) and Ni(II) ions with Schiff base N-[2-thienylmethylidene]-2-aminothiophenol (TNATPh). 

The method may also be applied to the analysis of silver halides by dissolution in excess of cyanide solution and back-titration with standard silver nitrate. It can also be utilised indirectly for the determination of several metals, notably nickel, cobalt, and zinc, which form stable stoichiometric complexes with cyanide ion. Thus if a Ni(II) salt in ammoniacal solution is heated with excess of cyanide ion, the [Ni(CN)4]2 ion is formed quantitatively since it is more stable than the [Ag(CN)2] ion, the excess of cyanide may be determined by the Liebig-Deniges method. The metal ion determinations are, however, more conveniently made by titration with EDTA see the following sections. 

Nickel s most common oxidation state is +2, and the green color of aqueous solutions of nickel salts is due to the presence of [Ni(H20)6]2+ ions. 

The adsorptivity and the reactivity of the 2-hydroxy oxime were well simulated by the MD simulations as shown in Fig. 5 where the polar groups of — OH and = N — OH of the adsorbed LIX65N molecule are accommodated in the aqueous phase so as to react with Ni(II) ion in the aqueous phase [18], This is the reason why the reaction rate constants of Ni(II) at the interface have almost same magnitude as those in aqueous phase. 

Photo-oxidation of carotenoids in Ni-MCM-41 produces an intense EPR signal (Figure 9.11) with -value 2.0027 due to the carotenoid radical another, less intense EPR signal, with =2.09 is attributed to an isolated Ni(I) species produced as a result of electron transfer from the carotenoid molecule to Ni(II). It has been reported that Ni(I) ions prepared upon reduction of Ni(II)-MCM-41 by heating in a vacuum or in dry hydrogen exhibits an EPR spectrum with , =2.09 and N=2.5... 

Hartmann et al. 1996). The gN component is often too weak to observe. The Ni(I) EPR signals were not detected upon 350 nm irradiation of Ni-MCM-41 samples before adsorption of carotenoids. Detected at 9 GHz, EPR signals of an isolated Ni(I) species with =2.09 provide direct evidence for the reduction of Ni(II) ions by carotenoids. 

The crystal structures of [Fe(2,6-bis(triazol-3-yl)pyridine)2](N03)2.4H20 and [Ni(2,6-bis(triazol-3-yl)pyridine)2]Cl2.3H20 revealed that the tridentate ligand coordinates to the metal(II) ion using both N-4 atoms of the two... 

When writing defect formation equations, the strategy involved is always to add or subtract elements to or from a crystal via electrically neutral atoms. When ionic crystals are involved, this requires that electrons are considered separately. Thus, if one considers NiO to be ionic, formation of a VNi would imply the removal of a neutral Ni atom, that is, removal of a Ni2+ ion together with two electrons. Similarly, formation of a VQ would imply removal of a neutral oxygen atom, that is, removal of an O1 2- ion, followed by the addition of two electrons to the crystal. An alternative way to express this is to say the removal of an O2- ion together with 2h. Similarly, only neutral atoms are added to interstitial positions. If ions are considered to be present, the requisite number of electrons must be added or subtracted as well. Thus, the formation of an interstitial Zn2+ defect would involve the addition of a neutral Zn atom and the removal of two electrons. 

Ammonia also forms clusters in the gas phase and the reactions of ammonia clusters with bare metal ions have been studied (61). The ammonia clusters probed by electron impact as [(NH3) H]+ showed a monotonic decrease in intensity with increasing value of n, but the metal complex ions [M(NH3) ]+ showed intensity gaps. Thus for most of the metals the [M(NH3)2]+ ion was much more intense than the [M(NH3) ]+ ions, where n 2, and so the coordination number 2 was reported to be the favored coordination number in the first coordination sphere. The favored ions M(NH3)m]+ were n = 2 for Cr+, Mn+, Fe+, Co+, Ni+, and Cu+, and n = 4 for V+. The non-transition metal Mg+ and Al+ had the favored coordination number of 3. 

The reactions of metal bpy ions with oxygen have been studied (193). The bis(bpy) complex ions, [M(bpy)2]2+, of Cr, Ru, and Os formed the dioxygen adducts, whereas the similar complex ions of Mn, Fe, Co, Ni, and Cu were unreactive. The CID of the [M(bpy)202]2+ ions exhibit interesting differences. 

Passing to the polypyridine complexes, Figure 111 shows the octahedral geometry of the [Ni(bipy)3]2+ ion.163... 

Larsson et al. 92) demonstrated also that the anisotropic pseudorotation model could be used for direct fitting of experimental PRE data for aniline protons in the complex between a Ni(II) chelate (Ni(II)(dpm)2) and ring-deuterated aniline in toluene-dg solution. The Ni(II) ion is in this case surrounded by four oxygen atoms and two nitrogen atoms, which should result in a sizable static ZFS, which indeed is confirmed by the fits. 

---