Coordination species of rhenium(V) in hydrochloric acid solutions and in the presence of other ligands

Abstract

The coordination species of rhenium(V) have been studied in a solution of hydrochloric acid of different concentrations. The pentachlorooxorhenium(V) ion, ReOCl 5 2− is found to undergo an acid hydrolysis with a subsequent oxidation. This finding rules out the disproportionation mechanism generally accepted by other authors. The resulting hydrolysed species, (ReOCl 4H 2O −), modifies the spectrum of the solution. The trans-effect of the oxygen atom labilizes the chlorine atom located on the sixth position of ReOCl 5 2− and thus facilitates its substitution by a water molecule or any other unidentate ligand which gives a stronger bond to rhenium. ReOCl 4H 2O − is found to form a rhodanide complex over a wide concentration range. This complex has the composition ReOCl 4CNS 2− ( β 1 = (2·4 ± 0·4) . 10 4). In the presence of other suitable bidentate ligands ( o-mercaptobenzoic acid), ReOCl 4H 2O − is subject to more profound changes in its electronic structure, changes which affect the double bond, ReO. The rhenium compound with the o-mercaptobenzoic acid is Re(MBA) 2Cl, where MBA is the divalent anion of the mercaptobenzoic acid. The chromatographic behaviour of Re(V) in hydrochloric acid solutions and also that of Re(V) in the presence of other oxidation states of rhenium is quantitatively studied on Whatman DE-20 chromatographic paper.