XPu(CO)_<i>n</i> (X = B, Al, Ga; <i>n</i> = 2 to 4): π Back-Bonding in Heterodinuclear Plutonium Boron Group Compounds with an End-On Carbonyl Ligand

The bonding situation and the oxidation state of plutonium in heterodinuclear plutonium boron group carbonyl compounds XPu(CO)n (X = B, Al, Ga; n = 2 to 4) were investigated by systematically searching their ground-state geometrical structures and by analyzing their electronic structures. We found that the series of XPu(CO)n compounds show various interesting structures with an increment in n as well as a changeover from X = B to Ga. The first ethylene dione (OCCO) compounds of plutonium are found in AlPu(CO)n (n = 2, 3). A direct Ga–Pu single bond is first predicted in the series of GaPu(CO)n, where the bonding pattern represents a class of the Pu → CO π back-bonding system. There is a trend where the Pu–Ga bonding decreases and the Pu–C(O) covalency increases as the Ga oxidation state increases from Ga(0) to Ga(I). Our finding extends the metal → CO covalence back-bonding concept to plutonium systems and also enriches plutonium-containing bonding chemistry

Electronic Structures and Unusual Chemical Bonding in Actinyl Peroxide Dimers [An₂O₆]²⁺ and [(An₂O₆)(12-crown‑4 ether)₂]²⁺ (An = U, Np, and Pu)

As known, actinyl peroxides play important roles in environmental transport of actinides, and they have strategic importance in the application of nuclear industry. Compared to the most studied uranyl peroxides, the studies of transuranic counterparts are still few, and more information about these species is needed. In this work, experimentally inspired actinyl peroxide dimers ([An2O6]2+, An = U, Np, and Pu) have been studied and analyzed by using density functional theory and multireference wave function methods. This study determines that the three [An2O6]2+ have unique electronic structures and oxidation states, as [(UVIO2)2(O2)2–]2+, [(NpVIIO2)2(O2–)2]2+, and mixed-valent [(PuVI/VO2)2(O2)1–]2+. This study demonstrates the significance of two bridging oxo ligands with at most four electron holes availability in ionically directing actinyl and resulting in the unusual multiradical bonding in [(PuVI/VO2)2(O2)1–]2+. In addition, thermodynamically stable 12-crown-4 ether (12C4) chelated [(An2O6)(12C4)2]2+ complexes have been predicted, that could maintain these unique electronic structures of [An2O6]2+, where the An ← O12C4 dative bonding shows a trend in binding capacity of 12C4 from κ4 (U) to κ3 (Np) and κ4 (Pu). This study reveals the interesting electronic character and bonding feature of a series of early actinide elements in peroxide complexes, which can provide insights into the intrinsic stability of An-containing species