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 PuIII/PuIV solid-state compound, Pu3(DPA)5(H2O)2 (DPA = 2,6-pyridinedicarboxylate). The properties of this compound are benchmarked by the pure PuIII and PuIV dipicolinate complexes, [PuIII(DPA)(H2O)4]Br and PuIV(DPA)2(H2O)3·3H2O, as well as by a second mixed-valent compound, PuIII[PuIV(DPA)3H0.5]2, that falls into class I instead. Metal-to-ligand charge transfer is involved in both the formation of Pu3(DPA)5(H2O)2 and in the IVCT.
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This material is based upon work supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Heavy Elements Chemistry Program under award number DE-FG02-13ER16414. We are especially grateful for the assistance and supervision by the Office of Environmental Health and Safety at Florida State University, specifically J. A. Johnson and A. L. Gray of the Office of Radiation Safety for their facilitation of these studies. Magnetization measurements using the VSM SQUID MPMS were performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative agreement number DMR-1157490, the State of Florida, and the US Department of Energy. We are grateful for helpful discussions with N. M. Edelstein, M. P. Jensen and G. Liu.
The authors declare no competing financial interests.
Supplementary information (PDF 1154 kb)
Crystallographic data for compound PuIII-1. (CIF 3654 kb)
Crystallographic data for compound PuIV-2. (CIF 3474 kb)
Crystallographic data for compound PuIII,IV-3. (CIF 927 kb)
Crystallographic data for compound PuIV,III-4. (CIF 482 kb)
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Cary, S., Galley, S., Marsh, M. et al. Incipient class II mixed valency in a plutonium solid-state compound. Nature Chem 9, 856–861 (2017). https://doi.org/10.1038/nchem.2777
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