Periodic Trends in Actinyl Thio-Crown Ether Complexes

In-cavity complexes and their bonding features between thio-crown (TC) ethers and f-elements are unexplored so far. In this paper, actinyl­(VI) (An = U, Np, Pu, Am, and Cm) complexes of TC ethers have been characterized using relativistic density functional theory. The TC ether ligands include tetrathio-12-crown-4 (12TC4), pentathio-15-crown-5 (15TC5), and hexathio-18-crown-6 (18TC6). On the basis of the calculations, it is found that the “double-decker” sandwich structure of AnO₂(12TC4)₂²⁺ and “side-on” structure AnO₂(12TC4)²⁺ are changed to “insertion” structures for AnO₂(15TC5)²⁺ and AnO₂(18TC6)²⁺ due to increased size of the TC ether ligands. The actinyl monocyclic TC ether complexes are found to exhibit conventional conformations, with typical An–O_actinyl and An–S_ligand distances and angles. Chemical bonding analyses by Weinhold’s natural population analysis (NPA), natural localized molecular orbital (NLMO), and energy decomposed analysis (EDA), show that a typical ionic An–S_ligand bond with the extent of covalent interaction between the An and S atoms primarily attributable to the degree of radial distribution of the S 3p atomic orbitals. The similarity and difference of the oxo-crown and TC ethers as ligands for actinide coordination chemistry are discussed. As soft S-donor ligands, TC ethers may be candidate ligands for actinide recognition and extraction

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

Uranyl/12-crown‑4 Ether Complexes and Derivatives: Structural Characterization and Isomeric Differentiation

The following gas-phase uranyl/12-crown-4 (12C4) complexes were synthesized by electrospray ionization: [UO₂(12C4)₂]²⁺ and [UO₂(12C4)₂(OH)]⁺. Collision-induced dissociation (CID) of the dication resulted in [UO₂(12C4-H)]⁺ (12C4-H is a 12C4 that has lost one H), which spontaneously adds water to yield [UO₂(12C4-H)­(H₂O)]⁺. The latter has the same composition as complex [UO₂(12C4)­(OH)]⁺ produced by CID of [UO₂(12C4)₂(OH)]⁺ but exhibits different reactivity with water. The postulated structures as isomeric [UO₂(12C4-H)­(H₂O)]⁺ and [UO₂(12C4)­(OH)]⁺ were confirmed by comparison of infrared multiphoton dissociation (IRMPD) spectra with computed spectra. The structure of [UO₂(12C4-H)]⁺ corresponds to cleavage of a C–O bond in the 12C4 ring, with formation of a discrete U–O_eq bond and equatorial coordination by three intact ether moieties. Comparison of IRMPD and computed IR spectra furthermore enabled assignment of the structures of the other complexes. Theoretical studies of the chemical bonding features of the complexes provide an understanding of their stabilities and reactivities. The results reveal bonding and structures of the uranyl/12C4 complexes and demonstrate the synthesis and identification of two different isomers of gas-phase uranyl coordination complexes