Cobalt tetravalent

In studies of the concentrations of arsenic, bromine, chromium, copper, mercury, lead and zinc in south-eastern Lake Michigan, it was shown that these elements concentrated near the sediment water interface of the fine-grained sediments. The concentration of these elements was related to the amount of organic carbon present in the sediments (161). However, it was not possible to correlate the concentration of boron, berylium, copper, lanthanum, nickel, scandium and vanadium with organic carbon levels. The difficulty in predicting the behaviour of cations in freshwater is exemplified in this study for there is no apparent reason immediately obvious why chromium and copper on the one hand and cobalt and nickel on the other exhibit such variations. However, it must be presumed that lanthanium might typify the behaviour of the trivalent actinides and tetravalent plutonium. 

A few examples will illustrate the use of those terms. Chloro-pentammino-cobaitic chloride is written as [Co(NII3)5.Cl]Cl2, nitrito-aquo-tetrammino-eobaltic chloride as [Co(N I3) (NH3),(N02).n20 (. l2, and chloro-aquo-tetrammino-eobaltic chloride as [Co(NI13)4C1(1120)JC1 2. It will be observed that the co-ordination number in each of the complexes is six, and this is characteristic not only of cobalt-ammines, but also of many other complexes. Some metals, however, yield complexes with co-ordination number four. For example, tetrammino-cuprio sulphate, [Cu(NH3)1]S04, and tctrammino-platinous chloride, [Pt(NH3)4]Cl2, belong to this class. On the other hand, the co-ordinatioi i number of hexannnino-platinic chloride, [Pt(NIl3)0]Cl. is six, but the central metallic atom is tetravalent, hence there are four chlorine atoms in the outer dissociable zone. 

The trinitro-triammine cobalt has practically no conductivity.3 Werner s theory is further supported by the fact that by the introduction of a fourth molecule of ammonia into the triacido-triammine compound the solution becomes once more conducting, as one (N02) group is displaced from the co-ordination complex. The eobalt-ammino-compounds, therefore, containing fewer than three ammino-radicles, contain non-ionisable acidic radicle, and those containing more than three contain ionisable acidic radicles. The generalisation made in connection with the triammino-eompounds led, therefore, to the establishment of the constitution of other ammino-derivatives, and also to the constitution of some of the ammino-salts of divalent and tetravalent metals. 

In these compounds the maximum co-ordination, whether of tri-valent or tetravalent cobalt, appears to be six, as in the case of the simpler cobalt-ammines. 

Decammino-/i-oxy-dicobalticSalts,[(NH3)5Co". 02.Co/"(NH3)5] R4, and Decammino-jU-anhydroxy-dicohaltic Salts, [(NH3)5Co". Oa,CoIV(NH3)5]R5.—The two series of salts are very closely related, the latter being derived from the former. In the first series both cobalt atoms are trivalent in the second series one cobalt atom is assumed to be tetravalent. The oxy-salts were among the first of the polynuclear compounds prepared and examined, and in 1898 Werner and Mylius prepared the nitrate of the series and proved the constitution of these salts, showing them to be compounds formed by the union of two pentammino-cobalt nuclei by means of a molecule of oxygen. 

It is suggested that the extremely high rotations of these salts is due to tetravalent cobalt in the molecule, a suggestion which is supported by the marked diminution in rotation when the tetravalent cobalt is reduced to trivalent cobalt, as shown in the dicobaltic salts described. 

All three elements form complex ammino-derivatives. Those of osmium have been very little investigated those of iridium are analogous to the anunino-derivatives of platinum on the one hand and to the ammincs of cobalt and chromium on the other whilst the platinum derivatives resemble those of cobalt, save that the metal in the platinic derivatives is tetravalent and not trivalent as in the cobalt-ammines. 

In these the metal is divalent, tetravalent, and trivalent respectively. The ammino-iridous and the ammino-iridic salts correspond to the ammino-derivatives of palladium and platinum, whilst those of the sesqui-salts are analogous to the ammino-derivatives of cobalt, chromium, and rhodium. 

Platinum forms both platinous and platinie salts, in which the metal is divalent and tetravalent respectively. Both series of salts are capable of uniting with ammonia, forming complex ammines. The co-ordination number in the platinous series is four and in the platinie series six. The latter series correspond in many respects to the chromic and cobaltic ammino-salts, but as the metal is tetravalent, the maximum number of radicles outside the complex is four instead of three. Also, the ammino-bases from which the salts are derived are much more stable than those of chromium or cobalt. 

Cobalt, as a result of its place in the periodic system, should have a valency of nine. It is, however, mostly divalent and occasionally tervalent. Phosphorus can be tervalent as well as pentavalent sulphur is hexavalent in SOs and tetravalent in S02. At low temperatures the valency is such that the energy is a minimum, and which compounds will be formed can only be predicted when the energy can be calculated accurately. 

In terms of the development of an understanding of the reactivity patterns of inorganic complexes, the two metals which have been pivotal are platinum and cobalt. This importance is to a large part a consequence of each metal having available one or more oxidation states which are kinetically inert. Platinum is a particularly useful element of this pair because it has two kinetically inert sets of complexes (divalent and tetravalent) in addition to the complexes of platinum(O), which is a kinetically labile center. The complexes of divalent and tetravalent platinum show significant differences. Divalent platinum forms four-coordinate planar complexes which have a coordinately unsaturated 16-electron d8 platinum center, whereas tetravalent platinum is an 18-electron d6 center which is coordinately saturated in its usual hexacoordination. In terms of mechanistic interpretation one must therefore consider both associative and dissociative substitution pathways, in addition to mechanisms involving electron transfer or inner-sphere atom transfer redox processes. A number of books and articles have been written about replacement reactions in platinum complexes, and a number of these are summarized in Table 13. 

With its 3d84,r2 electron configuration, nickel forms Ni2 ions. Having a nearly complete 3d subshell, nickel does not yield a 3d electron as readily as iron and cobalt, and trivalent and tetravalent forms are known only in the hydrated oxides. Ni203 and Ni()2. and a few complexes. 

The latter statement refers to concurrent work by A. Bilewicz et al. [4] who studied the sorption of Zr, Hf, Th, and Rf on cobalt ferrocyanide surfaces. These ferrocyanides are known to be selective sorbents for heavy univalent cations such as Fr+, Cs+, and Rb+. However, some ferrocyanides such as Co ferrocyanide have been found to exhibit also particularly high affinities for tetravalent elements such as Zr4+, Hf4+, and Th4+ involving the formation of a new ferrocyanide phase between the 4+ cation and the Fe(CN)4 anion. 

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

The structural representation of the diformylcorrole derivatives 2.186 and 2.187 are apparently incorrect in A. W. Johnson s and coworkers 1973 paper. Indeed, these representations depict a tetraanionic ligand with a presumed tetravalent cobalt rather than the neutral cobalt(III) corrole species presented here and, it would appear, supported by the actual experimental details given in the very paper in question. 

Oxidations of metallocorroles have also been investigated by Vogel and co-workers." For instance, these researchers found that treatment of a-phenyl-cobalt(III) corrole 2.182 with Fe(C104)3 resulted in oxidation to cation 2.191 (Scheme 2.1.64). They also found that iron(III) salts could be used to effect oxidation of nitrosyl iron(III) corrole 2.192. In this case, however, it was a ic-cation radical species (i.e., 2.193), which was obtained upon by treatment with, for instance, iron(III) chloride (Scheme 2.1.65)." Similar oxidations of tetravalent complexes have also been carried out by Vogel and coworkers (see Scheme 2.1.60)." ... 

Orthopyroxene partitions nickel, cobalt, and manganese less than olivine and there are no clear correlations amongst these elements. Although low in abundance, orthopyroxene can be a significant reservoir for the trivalent cations vanadium, scandium plus tetravalent titanium, due to its high modal abundance, especially in depleted xenoliths with little or... 

Experiment 2 Molar Conductivity Measurements Considering Arrhenius s electrolytic theory of dissociation, Werner noted that evidence for his coordination theory may be obtained by determining the electrolytic conductivity of the metal complexes in solution. Werner and Jprgensen assumed that acid (ionic) residues bound directly to the metal would not dissociate and would thus behave as nonconductors, while those loosely held would be conductors. Molar conductivities of 0.1 molar percent aqueous solutions of some tetravalent platinum and trivalent cobalt ammines are given in Table 2.3. 

For the hydrotalcite samples (DS3 to 085), elemental analysis results point to Al/Co ratio of about 21/1, However, as the cobalt phtalocyanine anion is tetravalent, the Al/Co ratio was expected to be 4/1. This statement is correct if there is only the metal complex in the interlayers. In our case in addition to cobalt phtalocyanine, a meaningful contamination... 

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... 

Strontium ferrate (SrFe03) has the classic perovskite structure just like lanthanum cobaltate (LaCo03). In SrFe03, iron is tetravalent and strontium is bivalent. In LaCo03, both lanthanum and cobalt are trivalent. Although these pristine compounds themselves are very interesting, some combinations of the two acquire even more exciting properties. 

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