Iridate , hexachloro

Potassium Pentachloro-pyridino-iridite, [Ir pyCl5]K2, is prepared by heating a mixture of potassium hexachloro-iridite, [IrCl6]K3, and pyridine at 100° C. It is a reddish-brown salt which forms an orange-coloured solution in water, and on heating with chlorine yields pentachloro-pyridino-iridic acid, [Ir pyCljjH. 

Nearly any primary alcohol serves as a substrate with the exception of methanol and ethanol. Ferricyanide (17, 18), porphyrexide (18), and hexachloroiridate(IV) (18) can replace oxygen as oxidant. Hexachloro-iridate(IV) is consumed to the exclusion of oxygen in aerobic mixtures. When hexachloroiridate(IV) and H202 serve as oxidant and reductant respectively, the normal reaction, vis-a-vis H202, is reversed, and oxygen is produced (18). 

The quantity of sodium hexachloroiridate(IV), obtained from the complete consumption of 1.7 g. (8.85 mmoles) iridium metal in the manner described elsewhere,4 or 5.0 g. of the commercial hexahydrate is dissolved in 100 ml. of ethanol and the solution immediately filtered. A solution of 1.4 g. (9.4 mmoles) of sodium iodide in 50 ml. ethanol is then added to the solution. The fast reduction of the iridate(IV) ion, [IrCl6]2-, to iridate-(III), [IrCh]3-, by iodide ions is a well-known reaction 5 when it is carried out under these conditions, the sodium hexachloro-iridate(III) precipitates almost quantitatively and can easily be filtered, washed with ethanol, and dried at 100°. 

Krogmann et al. (516) have also reported the preparation of the isoelectron-ic mixed valent Ir2(C0)4Cl2(02CCH3) species from a mixture of hexachloro-iridate(IV) and formic and acetic acids. Preliminary powder x-ray data indicate that the dinuclear species possess extremely short Ir-Ir spacings of 2.78 A and a helical superstructure of 0.7 A in diameter. Further work is necessary to clarify the physical and chemical properties of these Ir - complexes in solution and the solid state. 

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