Divalent ions nickel

The coordination number of the chelated metal atom determines the number of linkages to functional groups. It is typically greater than the valency of the metal ion for example, the divalent ions of copper and nickel have coordination numbers of four, and the trivalent ions of chromium, cobalt, iron a coordination number of six. In the case of iron the coordination number six applies for the di- and trivalent forms. 

Kadyrov et al., who studied electrochemical hydrogen evolution on indium electrodes in the presence of an ultrasonic field [144], have also proposed a mechanism of ultrasound action on the cathodic reduction of indium [145]. Other workers have looked at the effect of ultrasound on the electroreduction of nickel and cobalt divalent ions catalyzed by ligands [146], obtaining similar results. 

The element nickel is a Group VIII metal which is part of the first transition series. Elemental nickel has the outer sphere electron configuration 3d 4s and readily yields the 4s electrons to give the divalent ion... 

In an ideal 5-V spinel cathode material, the manganese ion is tetravalent and the redox species are foreign metal ions. Nickel, copper, iron, cobalt, and chromium are known as a foreign metal The highest 5-V capacity is obtained for the composition of LiM(, Mn and LiMMnO, where M is divalent and divalent, respectively. Although a capacity of 145-147 mAh/g can be expected for the divalent metal (Ni, Cu) under the two-electron transfer mechanism, only LiNij MUj... 

In contrast, if the divalent ion is smaller than iron(II), as is the case for cobalt(Il) and nickel(II), which have ionic radii of 0.072 and 0.070 nm respectively, then substitution will place iron in a smaller than expected lattice site. In this case the positive lattice pressure will produce shorter iron-ligand bonds, and a stronger effective crystal field potential which will favour the low spin configuration and/or a higher spin crossover temperature. This is exactly what is observed in a series of... 

Nickel is an activator of a number of enzymes, e. g., alkaline phosphatase and oxalacetate decarboxylase, which can also be activated by other divalent metal ions. Nickel also enhances insulin activity. The essential role of nickel has been established by inducing deficiency S5nnptoms in feeding experiments with chickens and rats. These symptoms include changes in the liver mitochondria. The daily intake in food amounts to 150-700 pg. The nickel requirement is estimated to be 35-500 pg/day. 

FE An electrochemical cell is composed of pure O nickel and pure iron electrodes immersed in solutions of their divalent ions. If the concentrations of Ni and Fe ions are 0.002 M and 0.40 M, respectively, what voltage is generated at 25°C (The respective standard reduction potentials for Ni and Fe are -0.250 V and -0.440 V.)... 

By isomorphous substitution, the Mg2+ ion can be replaced by other divalent ions such as Ni2+ and Co + or by monovalent cations such as Li. In this latter case, the excess of charge must be compensated by an additional exchangeable cation located between the layers. Talc and chrysotile of cobalt or nickel were prepared in our laboratory as precursors Of Ni and Co/SiOg catalysts... 

Divalent copper, cobalt, nickel, and vanadyl ions promote chemiluminescence from the luminol—hydrogen peroxide reaction, which can be used to determine these metals to concentrations of 1—10 ppb (272,273). The light intensity is generally linear with metal concentration of 10 to 10 M range (272). Manganese(II) can also be determined when an amine is added to increase its reduction potential by stabili2ing Mn (ITT) (272). Since all of these ions are active, ion exchange must be used for deterrnination of a particular metal in mixtures (274). 

NE is unstable in light and air, especially at neutral and alkaline pH. Oxidation to noradrenochrome occurs in the presence of oxygen and such divalent metal ions as copper, manganese, and nickel. 

Metal ion complexation rates have been studied by the T-jump method. ° Divalent nickel and cobalt have coordination numbers of 6, so they can form complexes ML with monodentate ligands L with n = 1—6 or with bidentate ligands, n = 1-3. The ligands are Bronsted bases, and only the conjugate base form undergoes coordination with the metal ion. The complex formation reaction is then... 

It is worthwhile to point out that lithium extraction from inverse spinels V[LiM]04, such as V[LiNi]04 and V[LiCo]04 takes place at high voltage, typically between 4 and 5V [153]. Lithium is extracted from the octahedral 16d sites of these spinels with a concomitant oxidation of the divalent nickel or cobalt ions. From a structural point of view, this can be readily understood because lithium must be dislodged from the 16d octahedral sites, which are of low-energy, into neighboring energetically unfavorable 8b tetrahedra, which share all four faces with 16d sites that are occupied by nickel or cobalt and by lithium. Lithium extraction reactions... 

Cobaltites with spinel stractnre have compositions MC02O4, where M is a metal forming divalent cations, snch as zinc, cadminm, magnesinm, nickel, manganese, and divalent cobalt. In contrast to the perovskites, the cobaltites have a rather high catalytic activity already at room temperatnre. Experiments show that the activity increases with increasing spinel structure content (i.e., increasing number of Co ions) of the catalyst snrface. The trivalent cobalt ions promote the withdrawal of... 

Complexes with pyridine-2,6-diimine ligands, five-coordinate [NiX2(174)] (X = C1, Br) or six-coordinate [Ni(174)2]X2, were usually assumed to have innocent neutral ligands. The X-ray structure and spectroscopic characteristics of [Ni(174)2](PF6) confirm that the complex contains the neutral ligand ([174] ) and a divalent nickel ion.579 The cyclic voltamogram of this complex in CH2C12 shows three reversible one-electron-transfer processes at = 1.19 V, —1.30 V, and — 1.82V (vs. Fc+/Fc), of which the first is a one-electron oxidation, while the other two correspond to two successive one-electron reductions. The spectroscopic data allow one to assign these processes as follows ([174]1 is a one-electron reduced radical form of [174] ) [Nini(174)°2]3+ [NiII(174)02]21 - " [NiI(174)°2]+ = " [NiI(174)°(174)1 ]°. 

Finally, the presence of the substituents on the nitrogen donors also influences the reactivity of the corresponding complexes significantly. Thus, utilization of the permethylated derivative in place of H2L23 drastically alters the Lewis-acidity of the metal ions, that is the coligands in the [Ni2(L19)(L )]+ compounds become more polarized than in the [Ni2(L23)(L )]+ complexes. In the latter complexes, the Lewis-acidity of the divalent nickel(II) ions is in large part consumed for the polarization of the six secondary NH functions. This explains why only the complexes of the permethylated macrocycle are able to activate and transform small molecules such as H20 or C02 (210,239,241). 

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