Two Neptunium(III) Mellitate Coordination Polymers: Completing the Series Np–Cf of Trans-Uranic An(III) Mellitates

• Published in: Inorganic chemistry 2022-11, Vol.61 (44), p.17730-17737
• Main Authors: Beck, Nicholas B., Bai, Zhuanling, Brannon, Jacob P., Martinez, Daniela Gomez, Grödler, Dennis, Long, Brian N., Poe, Todd N., Rotermund, Brian M., Albrecht-Schönzart, Thomas E., Sperling, Joseph M.
• Format: Article
• Language: English
• Subjects: Chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c02873

Two neptunium­(III) mellitates, 237Np2(mell)­(H2O)9·1.5H2O (Np-1α) and 237Np2(mell)­(H2O)8·2H2O (Np-1β), have been synthesized from 237NpCl4(dme)2 by reduction with KC8 and subsequent reaction with an aqueous solution of mellitic acid (H6mell). Characterization by single-crystal X-ray crystallography and UV–vis–NIR spectroscopy confirms that the neptunium is in its +3 oxidation state and both polymorphs are isostructural to the previously reported plutonium mellitates. Of the two morphologies, Np-1α is indefinitely stable in air, while Np-1β slowly oxidizes over several months. This is due to the change in the energy of the metal-ligand charge-transfer absorption exhibited by these compounds attributed to differing numbers of carboxylate bonds to Np­(III), where in Np-1β the energy is low enough to result in spontaneous oxidation.