Incipient class II mixed valency in a plutonium solid-state compound

Abstract

Electron transfer in mixed-valent transition-metal complexes, clusters and materials is ubiquitous in both natural and synthetic systems. The degree to which intervalence charge transfer (IVCT) occurs, dependent on the degree of delocalization, places these within class II or III of the Robin-Day system. In contrast to the d-block, compounds of f-block elements typically exhibit class I behaviour (no IVCT) because of localization of the valence electrons and poor spatial overlap between metal and ligand orbitals. Here, we report experimental and computational evidence for delocalization of 5f electrons in the mixed-valent Pu/Pu solid-state compound, Pu(DPA)(HO) (DPA = 2,6-pyridinedicarboxylate). The properties of this compound are benchmarked by the pure Pu and Pu dipicolinate complexes, [Pu(DPA)(HO)]Br and Pu(DPA)(HO)·3HO, as well as by a second mixed-valent compound, Pu[Pu(DPA)H], that falls into class I instead. Metal-to-ligand charge transfer is involved in both the formation of Pu(DPA)(HO) and in the IVCT.

Uranium(III)-carbon multiple bonding supported by arene δ-bonding in mixed-valence hexauranium nanometre-scale rings

“…XANES data, whether the white line is determined from the first or second derivative of the data, consistently place 3 in between uranium(III) and uranium(IV) standards suggesting the presence of both ions 67 – 69 . Mixed valence actinide(III/IV) complexes remain rare 72 – 76 , and we are not aware of any XANES studies of such species 68 , but the presence of Robin Day Class I or III systems has been inferred mostly by crystallographic data 72 – 76 . A single absorption feature for 3 and 4 does not rule out a Class I assignment for these complexes because the observed feature is a linear combination of the two oxidation state spectra that would have to be significantly different to deconvolute.…”

Synthesis and Characterization of Water Stable Uranyl(V) Complexes

“…[20] Thechemistry of the dipicolinate ligand was also studied for abroad range of heavier actinide ions. [21,22] Stability constant data previously measured in moderately acidic aqueous solutions (pH < 7) by spectrophotometry show that dpa 2À strongly binds both UO 2 2+ and NpO 2…”

Synthesis and Characterization of Water Stable Uranyl(V) Complexes

“…The structural, [17] the thermodynamic [18] and the kinetic [19] properties of the uranyl(VI) (right, Figure 1) and neptunyl(V) complexes of the dipicolinate ligand (dpa 2− ; H 2 dpa=pyridine‐2,6‐dicarboxylic acid), a low denticity analogue of dpaea 2− , have attracted numerous studies due to its relevance as an effective extractant of actinides for spent nuclear fuel reprocessing applications [20] . The chemistry of the dipicolinate ligand was also studied for a broad range of heavier actinide ions [21, 22] . Stability constant data previously measured in moderately acidic aqueous solutions (pH<7) by spectrophotometry show that dpa 2− strongly binds both UO 2 2+ and NpO 2 + [18] .…”