First Structural Characterization of a Protactinium(V) Single Oxo Bond in Aqueous Media

Abstract

The present work describes the first structural studies of protactinium(V) in sulfuric and hydrofluoric acid media using X-ray absorption spectroscopy. The results show unambiguously the absence of the trans-dioxo bond that characterizes the other early actinide elements such as U and Np. In concentrated sulfuric acid (13 M), Pa(V) is proved to exhibit a single oxo bond as postulated in the literature for species in more dilute media. In a 0.5 M HF medium, XANES and EXAFS spectra indicate the absence of any oxo bond: Pa(V) exists in the form of a pure fluoro complex.

A chromatographic separation of neptunium and protactinium using 1-octanol impregnated onto a solid phase support

“…All previous approaches to 237 Np/ 233 Pa separation (to our knowledge) include the use of HF or H 2 SO 4 for separation and isolation of 233 Pa and 237 Np [16,24]-and prevention of Pa hydrolysis through the separation procedure [31]. The use of these reagents not only adds significantly to potentially hazardous radioactive mixed waste, but also requires additional steps to remove F -and SO 2À 4 for subsequent source preparation and radioactivity measurements [6,15].…”

“…Although it is well understood that Np(V) in aqueous conditions forms the linear dioxo-neptunyl cation, NPO þ 2 [2,37], less is known about the molecular features of the Pa complex in solution. It was hypothesized, and recently demonstrated, that Pa forms a linear mono oxo-protactinyl moiety [31,37,38] [2].…”

Elucidating Protactinium Hydrolysis: The Relative Stabilities of PaO2(H2O)+ and PaO(OH)2+

“…33 Almost 40 years later, an X-ray absorption study confirmed the mono-oxo bond in PaO(SO 4 ) 3 3− present in a 13 M H 2 SO 4 solution. 34 Oxalate and diethylenetriaminepentaacetate can also form complexes containing Pa−O bonds. 35 39 Theoretical studies have also examined essential aspects of the chemistry of Pa. 40−42 The calculated structure of PaO 2 + is linear and its electronic structure is similar to those of higher linear actinides, where the 5f orbital contribution to bonding is important.…”

Combining theoretical chemistry and XANES multi-edge experiments to probe actinide valence states

“…Protactinium, as the first actinide with 5f-electrons involved in bonding (ground state electronic configuration 5f 2 6d 1 7s 2 ), occupies a key position in the actinide series. At formal oxidation state (V) (its most stable oxidation state in solution as well as in the solid state) Pa(V) corresponds also to the formal 5f 0 electronic configuration and has been reported to occur as a mono oxo Pa(V)O 3þ cation [1]. The existence of the PaO 2 þ form in solution and in solid state has never been reported.…”