Iridium salts

It is found that the tetra-isoamylphosphonium cation does not take a roughly spherical shape but accommodates an iodide ion 480 pm from the phosphorus atom. Neutron diffraction of phosphonium bromide crystals shows no evidence of hydrogen-bonding. The ructures of bis(trimethylphosphine)silicon tetrachloride and the iridium salt (134) are also reported. 

Ammonia unites readily with iridium salts, giving rise to complex ammino-derivatives. The first compounds described appear to be ammines analogous to those of palladium and platinum, to which they were compared by Berzelius 8 and Skoblikoff.4 A further series were described by Claus 5 wliich he represented like those of ammino-rhodium salts, as they bore a marked resemblance to these. After Jorgensen had established the constitution of the ammines of rhodium, cobalt, and chromium salts, Palmaer gave similar constitution to the iridium compounds. 

Aquo-pentammino-iridium Nitrate, [Ir(NH3)sH20](N03)3, is formed when the corresponding base, [Ir(NH3)5H20](0H)3, produced by boiling an acido-pentammino-iridium salt with aqueous potassium hydroxide, is treated with nitric acid. It is precipitated in colourless microscopic plates, and on heating to 100° C. it is transformed into nitrato-pentammino-iridium nitrate. An aqueous solution of the salt is transformed into the nitrato-salt on boiling, and the reverse reaction takes place when an aqueous solution of nitrato-pentammino-iridium nitrate is boiled. The same reaction is observed with the corresponding pentammino-rhodium compound. 

The nitro-pentammino-iridium salts resemble those of chromium, cobalt, and rhodium, and react similarly towards reagents, but they are more stable towards acids. They give on long heating with hydrochloric acid chloro-pentammino-derivatives, but are not decomposed by concentrated nitric acid nor by aqua-regia, and only slowly decompose on heating with concentrated sulphuric acid at 100° C. ... 

The dinitrito-salts do not decompose with concentrated acids the salts are mostly soluble in water, and again are more stable than the corresponding cobalt salts, which react easily with acids with replacement of nitro-groups. Ammonia attacks the cobaltic series, forming nitrito-pentammino-salts, whereas very little nitrito-pentammino-iridium salt is produced even on heating the dimtrito-tetrammino-iridium salts with ammonia in a closed tube to 200° C.2... 

Two series of complex iridium salts corresponding to the hexammino-and diacido-iridium salts have been prepared containing ethylene-diamine. These have the same general characteristics as the ammino-salts. Both series have been resolved into optically active isomers, the dinitrito-series by means of d- and 1-bromo-camphor sulphonic acid, and the triethylenediamino-series by d- and 1-nitro-camphor. Attempts have been made to prepare etliylenediamino-derivatives containing tetravalent iridium. Thus, sodium hexaehloro-iridate, [IrCl6]Na2, reacts with ethylenediamine, but the products are syrupy and cannot be purified. Derivatives of trivalent iridium, however, have been prepared. These are crystalline and fairly easily purified. The... 

Triethylenediamino-iridium Salts, [Iren3]R3.—From the mother-liquor after crystallisation of dinitro-diethylenediamino-iridium d-camphor sulphonate, the d-camphor sulphonate of racemic triethylene-diamino-iridium crystallises. 

Ammino-derivatives of Osmium Compounds—Ammino-derivatives of Iridium Salts—Derivatives of Iridous, Iridic, and Iridium Sesqui-salts. 

Iridium salts are of current interest as sensitizers for internal latent image formation (189,190). The iridium ions are incorporated in the grains during their preparation, probably as a complex associated with silver ion vacancies. 

Protonation of dienol complexes (53) with hexafluorophosphoric acid in diethyl ether affords air-stable salts (55) in high yield [Eq. (27)] (206). While the iron derivatives (21) are rapidly hydrolyzed, the cyclopentadienyl rhodium and iridium salts (55) are much less reactive (207). 

As obtained in this way the platinum usually contains some 2 per cent, of iridium, precipitated along with the ammonium chlor-platinate as the corresponding iridium salt. A second refining serves to remove this iridium, a fairly pure platinum resulting. 

Reactions of Salts of Iridium,.—Hydrogen sulphide in excess causes the precipitation of dark brown iridium sesquisulphide, Ir2S3. If the iridium is present in solution in the tetravalent condition, as for example in the form of alkali chlor-iridates, M2IrCl8 or 2MQ.IrCld, the dark solution is first decolorised and a yellowish white precipitate of sulphur forms in consequence of the reduction of the iridium salt to the trivalent condition, namely, as IrCl3. When this has been accomplished the brown sesquisulphide is obtained. 

Metallic zinc reduces iridium salts to the metal, which is deposited as a black powder from solution. 

Estimation.—Iridium is conveniently estimated by igniting ammonium chlor-iridate in hydrogen, and weighing as metal. To this end, solutions containing iridium salts are evaporated with aqua regia, ammonium chloride added, and the chlor-iridate, (NH4)2IrCl6, collected and ignited. 

All of the carbonato cobalt(III) complexes reported here are reddish in color and extremely soluble in water. The rhodium complex is pale-yellow, whereas the iridium salt is virtually white they are both soluble in water. Treatment with dilute acid immediately gives the corresponding aqua complex with evolution of carbon dioxide. The characterization and the mechanistic details of acid hydrolysis of these complexes have been reported.3,4,11... 

It has also been found that this general method, which involves reductive carbonylation of an iridium salt under CO in an alcoholic solvent followed by addition of phosphine ligand, is not always reliable. On occasion the carbonylation step is unsuccessful, leading to formation of a dark suspension instead of the expected clear yellow solution addition of phosphine to the suspension affords no product. Although the reason for this erratic behavior is not clear, its frequency of occurrence appears to vary from one sample of starting iridium salt to another, suggesting that small amounts of impurities in some samples may be responsible. 

Although Werner considered both enantiomers of potassium tris-(oxalato)chromate(III) to be monohydrates, Charonnat and Dele-pine, on the basis of isomorphism with the corresponding iridium salt, proposed that they are dihydrates. The (+) enantiomer has been described as bluish red in the dry, pure condition. - The optical enantiomers are less soluble in water than the racemic mixture. Because of the high rate of racemization in water, recrystallization has been reported to be accompanied by a considerable loss of optical rotation. For the same reason, the optical rotation values reported by different workers are not directly comparable. ... 

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