Perrhenate complexes

Fig. 4.13. Crystal structures of the perrhenate complexes [H47a] + (ReO4)--3C - and [HgJf <= ReO4]5+-5(ReO4)--5H2O.

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. 

The full exploitation of the wide range of oxidation states of rhenium in radiopharmaceutical design requires not only a wide range of ligand donor types with varied n-donor and acceptor properties, but also suitable reducing agents to provide access to oxidation levels below (VII). This is because for radiopharmaceutical purposes the most conveniently man-factured form of rhenium radionuclides is perrhenate. The traditional routes to reduced rhenium complexes are not particularly amenable to use in a radiopharmaceutical context, where mild, rapid, and preferably... 

A greater tendency of rhenium complexes (compared to technetium analogues) to expand their coordination numbers has been invoked to rationalize the stronger interaction of the perrhenate ion with carboxylate ligands. This association has been suggested as a possible cause of the different quantitative biodistribution and excretion characteristics of pertechnetate and perrhenate perrhenate is accumulated in thyroid to a lesser extent and renally excreted more rapidly than pertechnetate [6]. 

The need to achieve high yield in one-pot synthesis, coupled to the relative kinetic inertness of rhenium complex (e.g. compared to technetium) and the mild conditions required has led to the development of useful versatile rhenium(V) intermediates that can be quickly prepared in quantitative yield, and are metastable, i.e. kinetically labile enough to react rapidly with the final chelator, again in high yield. The most widely used ligands suitable for this purpose are polydentate hydroxycarboxylic acids such as glucoheptonate [116a], citrate (47), tartrate (48), and 2-hydroxyisobutyric acid (49) [159]. Examples are discussed elsewhere in this chapter. They are typically used in the presence of Sn(II) to reduce Re(VII) to Re(V), at moderately elevated temperature (50-100 °C) at pH 2-3 (acid pH promotes reduction of perrhenate, presumably by facilitat-... 

Moeller and Vicentini (48) have reported the complexes of DMA with lanthanide perchlorates in which the number of DMA molecules per metal ion decreases from eight for La(III)—Nd(III) to six for Tm(III)—Lu(III).apparently due to the decrease in the cationic size. The complexes of the intermediate metal ions have seven molecules of DMA in their composition. Complexes of lanthanide chlorides with DMA (49, 50) exhibit a decrease in L M from 4 1 to 3 1 through 3.5 1. These complexes probably have bridging DMA molecules. The corresponding complexes with lanthanide iodides (51), isothiocyanates (52), hexafluorophosphates (57), nitrates (54, 55), and perrhenates (49, 56) also show decreasing L M with decreasing size of the lanthanide ion. However, complexes of DMA with lanthanide bromides (55) do not show such a trend. Krishnamurthy and Soundararajan (41) have reported the complexes of DPF with lanthanide perchlorates of the composition [Ln(DPF)6]... 

In the complexes of lanthanide perrhenates with TMU (78), DMA (56), and DMF (46), it has been observed that the i>3(Re04) vibration splits into three bands in the region 900 cm-1. This indicates the presence of coordinated perrhenate group (either C3v or C2v symmetry). The ionic perrhenate group exhibits only one band in this region. 

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