Cobalt complexes 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. 

Complexes of cobalt (III) containing coordinated perrhenate ion have not previously been reported. % They are of special interest because of their close relationship to the unstable perchlorate complexes and are of use in studies on the mechanism of hydrolysis. Since the equilibrium constant of formation is small and [Co(NH )5(HjO)](Re04) -2H20 is relatively insoluble, the present procedure is similar to that used previously for mom common complex ions. 

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