Mössbauer spectroscopy of neptunyl species

• Published in: Journal of solid state chemistry Vol. 178; no. 2; pp. 545 - 553
• Main Authors: Kalvius, G.M., Dunlap, B.D., Asch, L., Weigel, F.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-02-2005
• Subjects: [formula omitted]-electron structure; Bond properties; Mössbauer spectroscopy; Neptunium compounds; Neptunyl; Neptunium compounds; Bond properties; 5 f -electron structure; Neptunyl; Mössbauer spectroscopy
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2004.07.025

Systematics of hyperfine parameters from
237Np Mössbauer
resonance data of compounds with Np in a high formal charge state
(
Np
6
+
,
Np
7
+
)
are discussed with respect to electronic structure properties. In neptunyl(VI) species, we find a linear correlation between the isomer shift and the strength of quadrupole interaction. Both scale linearly with the actinide–oxygen bond length, stressing the central role of this parameter. Some compounds show paramagnetic relaxation spectra which makes their analysis difficult. The hyperfine interactions are often not rotational symmetric indicating a deviation from the simple linear O–Np–O configuration. Mössbauer spectra of
NpO
3
·
2
H
2
O
reveal that this compound should be described as a neptunyl. A comparison of hyperfine parameter systematics indicates that the Np valence electron properties in Np(VII) species are basically similar to those in Np(VI) neptunyls.
Linear correlations of the electric field gradient
eq
(
▴
) and the charge density
ρ
e
(0) (
▾
) at the neptunium nucleus in neptuny (VI) compounds with the actinide–oxygen bond length in isomorphous uranyl compounds. A similar relation can be established for
Np
7
+
species.
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