The partition coefficients of nitratonitrosylruthenium complexes between nitric acid and TBP phases

Abstract Both the non-ionic trinitrato complex and the tetranitrato acid of nitrosylruthenium (III) have relatively high partition coefficients at 0° in TBP-diluent-HNO 3 systems, that of the tetranitrato acid being slightly the higher for >10% TBP. The acid also forms a second organic phase more rapidly. The partition coefficients indicate that it is only the free TBP, i.e. that not present as TBP·HNO 3 , that is available for the extraction of these complexes. For the trinitrato complex, both its extraction behaviour and the infra-red spectrum of a saturated TBP phase indicate that TBP groups are attached by hydrogen-bonding. The partition coefficients are consistent with the attachment of four TBP groups to the hydrogen atoms of the two aquo groups; the formation constant, calculated for this tetra-solvated complex is ∼2 × 10 4 over the range 5–30% TBP and 0·5–5 M aqueous nitric acid. The partition coefficients for the tetranitrato acid are also consistent with there being only hydrogen-bonded TBP groups in the organic phase, the cation of the ion-pair being [(TBP·H) 3 O] + .