Nontransition metal ions

In other work, solution complex formation of the pendant-arm ligands 1,4,10,13-tetraoxoa-7,16-diazacyclooctadecane-7-malonate and 1,4,10,13-tetraoxoa-7,16-diazacyclooctadecane-7,16-bis(malonate) has been investigated with a range of both transition and nontransition metal ions the 1 1 manganese(II) complexes of these species have been reported to show stabilities (log Ai values) of 7.41 and 5.60, respectively, in water (7=0.15, 25°C). 

Coordination of perchlorate to transition and nontransition metal ions has been well established, though in most of the cases the metal-perchlorate bond is rather weak and has been termed as semicoordination (1). The coordination that can be recognized in the solid state may frequently break down in solution, particularly in aqueous medium (the solvent molecule replacing the coordinated perchlorate). 

Table 6 shows the major metal oxides and the iron oxide impurity levels of typical borosilicate Type I glass. Up to 0.05% by weight (500 ppm) iron oxide as Fe O may exist in the borosilicate Type I glass. Thus, the increase in iron levels with time likely reflects a slow leaching of iron from the glass vial. Consistent with this explanation is that similar increases in silicon, aluminum, calcium, and barium levels are also observed in older product lots as shown in Table 6. Note that these nontransition metal ions are not known to participate in the type of reactions depicted in Figure 6. Furthermore, it is not clear if the expected increase in iron leaching from amber vials (Table 6) will be readily compensated for by the reduced light transmission at the causative wavelengths offered by utilizing the amber vial as the primary package.

Nonradiative relaxation of transition-metal chelates is so efficient that these species seldom fluore.sce. It is worth noting that most transition metals absorb in the UV or visible region, while nontransition metal ions do not. For this reason, fluorescence is often considered complementary to absorption for the determination of cations. 

Fiigh-spin manganese(III) and iron(III), having no CFSE, resemble the nontransition metals in having no preferred geometry. This enhances their ability to replace nontransition metal ions of similar size in minerals and complexes. An example is in ferrites, M(II)Fe(III)204, where the spinel structure is generally preferred, except that when M(II) is d , the inverse spinel structure is stabilized, with all the M(II) in octahedral sites (CFSE) and the iron(III),... 

Pursuant to our interest in substituted amides as ligands, we studied reactions of NMBuL with nontransition metal ions. ... 

Complex ions are commonly formed by transition metals, particularly those toward die right of a transition series (MCr — 3oZn in the first transition series). Nontransition metals, including Al, Sn, and Pb, form a more limited number of stable complex ions. 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

This relationship, which cannot be derived here, applies well if the unpaired electrons are situated on a nontransition metal atom or an element of the first transition series. It is inapplicable to the rare-earth and actinide ions in solution, for with these, the orbital angular momentum of the highly eccentric / electrons becomes comparable to their spin moment. 

The chemistry of coordination compounds is a broad area of inorganic chemistry that has as its central theme the formation of coordinate bonds. A coordinate bond is one in which both of the electrons used to form the bond come from one of the atoms, rather than each atom contributing an electron to the bonding pair, particularly between metal atoms or ions and electron pair donors. Electron pair donation and acceptance result in the formation of a coordinate bond according to the Lewis acid-base theory (see Chapter 5). However, compounds such as H3N BC13 will not be considered as coordination compounds, even though a coordinate bond is present. The term molecular compound or adduct is appropriately used to describe these complexes that are formed by interaction of molecular Lewis acids and bases. The generally accepted use of the term coordination compound or coordination complex refers to the assembly that results when a metal ion or atom accepts pairs of electrons from a certain number of molecules or ions. Such assemblies commonly involve a transition metal, but there is no reason to restrict the term in that way because nontransition metals (Al3+, Be2+, etc.) also form coordination compounds. 

The catalytic properties of H-, Li-, Na-, K-, Mg-, Ca-, Zn-, Cd-, and Al-forms of synthetic mordenite in the reactions of cyclohexane and n-pentane isomerization and benzene hydrogenation have been studied. The cation forms of mordenite that do not involve the metals of column VIII of the Mendeleyev Table show high activity in these reactions. To elucidate the mechanism of n-pentane isomerization, the kinetics of the reaction on H-mordenite have been studied. Carbonium ion is supposed to result from splitting off hydride ion from hydrocarbon molecule. Na-mordenite catalytic activity in benzene hydrogenation reaction decreases linearly with the increase of decationization. This indicates that cations are responsible for the catalytic activity of zeolite. The high activity of cations of nontransition metals in oxidation-reduction reactions seems to be quite unexpected and may provide evidence for some uncommon mechanism of benzene hydrogenation. 

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