Eight and Nine-Coordinate Plutonium (IV) Complexes of the f-Element Extractant 2,5-Bis(diphenylphosphinomethyl)benzene P,P'-dioxide Including Structural Characterization of a Plutonium (IV) Alkoxide

Abstract

The bidentate ligand 2,6-bis[(diphenylphosphino)-methyl]benzene P,P'-dioxide (POPO) is a liquid-liquid extraction agent for the separation of actinide and lanthanide ions in acid. When combined with an aqueous nitric acid solution of Pu(IV), POPO produces 1:1 coordination complexes Pu(POPO)(NO3)2Cl2 (3) and Pu(POP0)(NO3)3(OMe) (4). The former was isolated from a chloroform solution and the latter from a basic methanol solution. Monoclinic crystals of both complexes were characterized by single-crystal, X-ray diffraction analysis. Compound 3 is eight-coordinate, containing a bidentate POPO ligand, two bidentate nitrates, and two chlorides. Complex 4 is nine-coordinate and contains a bidentate POPO ligand, three bidentate nitrates, and one methoxide. The plutonium to oxygen distances, Pu-O(P), of the bound phosphine oxide moieties are 2.250(3) A and 2.238(3) A in complex 3, and 2.301(2) and 2.276(2) A in complex 4. Plutonium to nitrate distances, Pu-0(NO3), range from 2.447(4) A to 2.468(4) A in 3 and from 2.456(3) to 2.544(3) A in 4. The plutonium to chloride, Pu-Cl, distances in 3 are 2.600(3) and 2.572(2) A. Nine-coordinate complex 4 has a short 2.027(3) A plutonium to methoxide oxygen distance and is the first structurally characterized plutonium alkoxide containing complex.