Preference for Nitrogen versus Oxygen Donor Coordination in Uranyl- and Neptunyl(VI) Complexes

Abstract

The first actinyl phosphinimine complexes have been synthesized and, in the case of uranium, exhibit strong U-N interactions. Competition reactions clearly demonstrate a surprising preference for R3P=NH ligands over R3P=O in the system [AnO2Cl2(R3PX)2] (An = U(VI), Np(VI); R = Ph, Cy; X = O, NH). Spectroscopic evidence for N-donor coordination to [NpO2]2+ in solution indicates chemical similarities to the [UO2]2+ moiety.

Actinyl chemistry across the U, Np and Pu series

“…This N-donor preference has also been demonstrated for Np(VI) chemistry [27], representing our first foray into inert atmosphere transuranium chemistry. NpO 2 Cl 2 (R 3 PNH) 2 complexes have been characterized by both 1 H and 31 P NMR spectroscopy and Raman spectroscopy.…”

“…A large difference in chemical shift between the NH 1 H NMR signal (R = Ph ␦ 6.54 ppm, R = Cy, ␦ 5.82 ppm for trans isomers) compared to the uncomplexed ligand (Ph 3 PNH ␦ 1.01ppm, Cy 3 PNH ␦ −0.51 ppm) is observed. Moreover, a short U-N interaction is observed in the crystal structure (2.370(1)Å for R = Ph and 2.350(2)Å for R = Cy) compared to other uranyl containing N donor ligands [20,[27][28][29], suggesting a strong U-N bond. In order to gain further insight into these observations, relavistic, gradient corrected density functional theory has been used to study these compounds.…”

“…We have recently reported our initial investigations into phosphinimine chemistry with uranyl and neptunyl, and are contunuing to research this area [27]. The reaction with the N-donor phosphinimines (R 3 PNH) to solutions of UO 2 Cl 2 (R 3 PO) 2 resulted in the selective displacement of the P O ligands and the formation of the phosphinimine complexes UO 2 Cl 2 (R 3 PNH) 2 , which have been structurally characterised.…”

Actinyl chemistry at the Centre for Radiochemistry Research

“…benzaminato and bis-iminophosphorane). This chemistry has led to the formation of a complex with a Umethylene bond, coordination of an activated Lewis basic uranyl oxygen to a Lewis acid and direct displacement of phosphine for phosphinimine ligands, the latter also studied in the analogous {NpO 2 } 2+ system [19][20][21][22][23]. XAS has been used to prove that the bioreduction of {UO 2 } 2+ to U(IV) can occur via a {UO 2 } + intermediate [24] and that {UO 2 } 2+ can form oligomeric chloride complexes in certain high temperature alkali metal chloride molten salt systems [25][26].…”

Uranyl complexation by monodentate nitrogen donor ligands. A relativistic density functional study

“…Complexation by Ph 3 PNH was demonstrated to be favorable when compared with the corresponding O-donor ligand [16]. NCO has been shown to coordinate preferentially via the N center [17].…”