Organic perrhenates

Arsonium salts have found considerable use in analytical chemistry. One such use involves the extraction of a metal complex in aqueous solution with tetraphenyiarsonium chloride in an organic solvent. Titanium(IV) thiocyanate [35787-79-2] (157) and copper(II) thiocyanate [15192-76-4] (158) in hydrochloric acid solution have been extracted using tetraphenyiarsonium chloride in chloroform solution in this manner, and the Ti(IV) and Cu(II) thiocyanates deterrnined spectrophotometricaHy. Cobalt, palladium, tungsten, niobium, and molybdenum have been deterrnined in a similar manner. In addition to their use for the deterrnination of metals, anions such as perchlorate and perrhenate have been deterrnined as arsonium salts. Tetraphenyiarsonium permanganate is the only known insoluble salt of this anion. 

All of the known rhenium chalcogenide halides are stable in air. With the exception of RegSgCU, they are insoluble in water, acids, and the common organic solvents. They dissolve readily in hot, 50% KOH (263, 264). Re2S3Cl4 is soluble in water, and ethanol, but insoluble in nonpolar organic solvents. With acids, alkalis, or hot water, hydrolytic decomposition takes place. Alkaline solutions can be oxidized to produce perrhenate compounds. 

Rhenium(VII) trioxo-complexes with derivatives of the Klaui ligand (19) are stable in air and organic solvents, but slowly decompose in aqueous solutions yielding perrhenic [Re03(cpCo PO(OR)2 3)] can be prepared from Re20v, perrhenate, or by oxidation of the corresponding Re tricarbonyl complex. Reduction with phosphines in the presence of HBr... 

PERRHENIC ACID. HreC>4. Exists only in solution, commercially available as aqueous syrup. Strong very stable, monobasic acid extremely soluble in water and organic solvents. 

Because, of the veiy heavy ionic, weight (250) of the perrhenate ion, it is one of the heaviest simple anions obtainable in readily soluble salts. It has found use as a precipitant for potassium and some other heavy univalent ions also as a precipitant for such complex ions as Co(NH )( "+. and for the separation of alkaloids and organic bases. Perrhenate also is used in the fractional crystallization ot the rare-earth elements. 

The perrhenate anion is present in the organic superconductor materials (TMTSF)2Re04, where TMTSF = tetramethyltetraselenafulvalene, and (BEDT-TTF)4(Re04)2, where BEDT-TTF = bis(ethylenedithiolo)tetrafulvalene, and is also an important precursor to Re—Pt reforming catalysts and metathesis catalysts. The latter role has led to studies of the thermal decomposition, the laser Raman spectra and the X-ray photoelectron spectra of catalytically important perrhenates, especially NH4Re04 and Al(Re04)j. 

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