237 Np Mössbauer isomer shifts in neptunium chalcogenides

Reinvestigation of Np2Se5: A Clear Divergence from Th2S5 and Th2Se5 in Chalcogen–Chalcogen and Metal–Chalcogen Interactions

“…50−52 Previous structural and 237 Np Mossbauer spectroscopic studies have inferred that the Np in Np 3 Se 5 is mixed-valent with crystallographically unique Np 3+ and Np 4+ sites in a ratio of 2:1. 10,11 The usual shift in energy between An 3+ and An 4+ XANES edges are commonly observed to be approximately 4 eV for actinide oxides in solution and the solid state. 53,54 However, the neptunium selenide compounds show a significant shift toward the edge energy of metallic Np when compared to Np 3+ dissolved in 1 M perchloric acid.…”

The Synthesis and Crystal Structure of NpSe3

“…Three years later Blaise et al carried out magnetic measurements on USe 3 and NpSe 3 and concluded that Np was +3 8. The more definitive 237 Np Mössbauer measurements were first interpreted as favoring the +3 oxidation state,9 but were later reinterpeted to favor the +4 oxidation state 3. From this brief summary it is clear that these heroic measurements on NpSe 3 , which is difficult to prepare and dangerous to handle, led to conflicting results regarding its structure and the formal oxidation state of Np.…”

“…In the assessment of their degree of localization neptunium is particularly important as it is at the border between tetravalent thorium and uranium and trivalent lanthanide‐like plutonium 1. To take the rich chemistry of the binary Np x Q y system (Q = chalcogen = S, Se, or Te) as an example,1 many of the reported compounds, including Np 3 Q 5 (Q = S, Se)2 and β‐NpS 2 ,3 are isostructural with Th or U analogues, within which Np is in the formal oxidation state of +4. In contrast, Np 2 Q 3 (Q = S, Se, Te),3–6 NpTe 2 ,6 and NpTe 3 6 are isostructural with Pu analogues, within which Np is +3.…”

“…To take the rich chemistry of the binary Np x Q y system (Q = chalcogen = S, Se, or Te) as an example,1 many of the reported compounds, including Np 3 Q 5 (Q = S, Se)2 and β‐NpS 2 ,3 are isostructural with Th or U analogues, within which Np is in the formal oxidation state of +4. In contrast, Np 2 Q 3 (Q = S, Se, Te),3–6 NpTe 2 ,6 and NpTe 3 6 are isostructural with Pu analogues, within which Np is +3. However, many of these Np x Q y compounds were characterized decades ago by X‐ray powder diffraction methods.…”

NpSe2: a Binary Chalcogenide Containing Modulated Selenide Chains and Ambiguous‐Valent Metal

“…These compounds are either isostructural with U analogues, containing predominantly tetravalent Np, or are isostructural with Pu/lanthanide analogues, containing trivalent Np. This dual behavior suggests that the 5f electrons of Np in chalcogenide environments may sit on the border between itinerant and localized regimes, thus allowing Np 3+ /Np 4+ redox chemistry within the chalcogenide sublattices –. Despite their potential for exhibiting interesting structural and electronic behaviors, Np chalcogenides remain largely unexplored compared with Th and U phases; even the simple binary systems have not been systematically studied…”