Platinum trivalent

Most metals can form some coordination compounds, but few form as many as trivalent cobalt. Others that do include trivalent chromium, and bi- and quadri-valent platinum. Trivalent chromium and quadrivalent platinum have the same coordination number and geometry as trivalent cobalt bivalent platinum has a coordination number of four with the groups around it arranged in a square. 

When tt o d eigenfunctions are available, as in trivalent cobalt, quadrivalent palladium and platinum, etc., six equivalent bond eigenfunctions of strength 2.923 and directed toward the comers of a regular octahedron can be formed. These form the bonds in a great many octahedral complexes. 

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. 

There are ammoniates of PtCl2, of halides of other platinum metals and of cobalt and nickel, too, some of which have been mentioned before in, Section 50. The cobalt complexes clearly show the importance of the completed d shells for the stability of the complex. Non complex compounds of trivalent cobalt are very unstable. Solutions of divalent cobalt in ammonia, however, are readily oxidized by air, because the NH3 complex of trivalent cobalt Co(NH3)6 3+ClT has eighteen electrons used in bond formation, whereas the ion Co(NH3) + would have nineteen electrons. 

In 1898, Cowper-Coles 2 claimed to have successfully effected the electrolytic reduction of an acid solution of vanadium pentoxide to metallic vanadium, but the product was subsequently shown by Fischer 3 to have been a deposit of platinum hydride. Fischer, in a series of over three hundred experiments, varied the temperature, current density, cathode material, concentration, electrolyte, addition agent, and construction of cell, but in not one instance was the formation of any metallic vanadium observed. In most cases reduction ceased at the tetravalent state (blue). At temperatures above 90° C. reduction appeared to proceed to the divalent state (lavender). The use of carbon electrodes led to the trivalent state (green), but only lead electrodes produced the trivalent state at temperatures below 90° C. Platinum electrodes reduced the electrolyte to the blue vanadyl salt below 90° C. using a divided cell and temperatures above 90° C. the lavender salt was obtained. 

Hydrogen also reduces pentavalent and tetravalent vanadium salts to the trivalent state in the presence of spongy platinum.1... 

The types of compounds formed by gold(I) and gold(III) often differ from those of other metals due to the constraints imposed by coordination number and electron count at the metal. Thus, for example, whereas 7r-bonded cyclopentadienyl complexes of palladium and platinum are numerous (336), and a copper(I) species of this type is known (337), cyclopentadienyl complexes of univalent (94, 96, 97) and trivalent (228) gold have invariably been found to be fluxional behavior, similar to that in dicyclopentadienylmercury, was involved (228). 

Chlorostannate and chloroferrate [110] systems have been characterized but these metals are of little use for electrodeposition and hence no concerted studies have been made of their electrochemical properties. The electrochemical windows of the Lewis acidic mixtures of FeCh and SnCh have been characterized with ChCl (both in a 2 1 molar ratio) and it was found that the potential windows were similar to those predicted from the standard aqueous reduction potentials [110]. The ferric chloride system was studied by Katayama et al. for battery application [111], The redox reaction between divalent and trivalent iron species in binary and ternary molten salt systems consisting of 1-ethyl-3-methylimidazolium chloride ([EMIMJC1) with iron chlorides, FeCb and FeCl j, was investigated as possible half-cell reactions for novel rechargeable redox batteries. A reversible one-electron redox reaction was observed on a platinum electrode at 130 °C. 

The high value of the potential 7t° = 1.8 V related to reaction (XXV-3) justifies in advance the assumption that the oxidation of trivalent chromium ions will be accompanied with an evolution of oxygen chiefly during the final stage of electrolysis, when the majority of Cr+++ ions has been oxidized to CrO ions. The material used for the anodes has a great influence upon the oxidation efficiency attained. It has been proved by experiments that oxidation will not ooeur on smooth platinum anodes at all. On platinum anodes coated with platinum black current efficiency is rather low, while with lead anodes which beoome coated with lead dioxide during eleotrolysis it is possible to reach... 

A2Pt207, similar to those reported for tin, ruthenium, titanium, and several other tetravalent ions. Trivalent ions which form cubic platinum pyrochlores range from Sc(III) at 0.87 A to Pr(III) at X.14 A. Distorted pyrochlore structures are formed by lanthanum (1.18 A) and by bismuth (1.11 A). Platinum dioxide oxidizes Sb203 to Sb2(>4 at high pressure. The infrared spectra and thermal stability of the rare earth platinates have been reported previously and will not be repeated here, except to point out the rather remarkable thermal stability of these compounds decomposition to the rare earth sesquioxide and platinum requires temperatures in excess of 1200 °C. 

When dissolved in sulphuric acid, platinic sulphate is reduced by oxalic acid, yielding a complex sulphate of trivalent platinum, namely, Pt2(0H)6.(S03)4.(0H)2.8-5H20. This yields well-defined triclinic prisms which gradually lose water when dried over sulphuric acid under reduced pressure, yielding a stable complex, Pt203.(S03)3.H2S04.4H20. This acid is dibasic, and yields crystalline potassium, sodium, and barium salts.1... 

The sesquioxide, Cr Oa, containing trivalent chromium, is an amphoteric oxide. It yields chromic salts, such as chromic chloride, CrCla, and sulphate, Cr2(S04)a, which are very stable and show great similarity to the ferric salts and to salts of aluminium as, for example, in the formation of alums. Since, however, chromic oxide functions as a weaker base than chromous oxide, the latter having a lower oxygen content, the chromic salts are more liable to hydrolysis than the chromous salts. This is well marked in the case of the chlorides. Again, in spite of the stability of chromic salts, only a slight tendency to form simple Cr " ions is exhibited, whilst complex ions are formed much more readily, not only complex anions, as in the case of iron and aluminium, but also complex cations, as in the extensive chromammine series. In this respect chromium resembles cobalt and platinum. 

Interest has continued in the extent to which factors affecting the planarity of the trivalent phosphorus atom have a bearing on the aromaticity and other properties of the phosphole ring system, and a review has appeared. A study of the coordination chemistry of phospholes bearing a sterically bulky substituent at phosphorus has shown that coordination to platinum results in increased pyramidality at phosphorus. In the same vein, an ab initio theoretical study of the triphosphole (357) has shown that the steric interac-... 

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. 

When an element exhibits different valences, these differ from each other by two. Thus, phosphorus is trivalent or quinquivalent platinum is bivalent or quadrivalent. 

Tetravalent plutonium in aq soln is reduced to the trivalent form by sulfur dioxide, hydroxylamine hydrochloride, hydrazine hydrochloride, the uranous ion, the iodide ion by shaking with mercury in chloride soln electrolytically at a platinum cathode. Tetravalent salts are pink or greenish form complexes very readily. 

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