Periodic Trends in Actinyl Thio-Crown Ether Complexes

Abstract

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 AnO(12TC4) and "side-on" structure AnO(12TC4) are changed to "insertion" structures for AnO(15TC5) and AnO(18TC6) 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 and An-S 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 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.

Electronic Structures and Properties of Actinide‐Bimetal Compounds An2O2 (An=Th to Cf) and U2E2 (E=N, F, S)

“…The same orbital occupation occurs in the 9 A g state of Np 2 O 2 with the valence electronic structure of 4 a g 2 (f) 4 (f) 4 , where the doubly occupied 4 a g bonding orbital is evidently hybridized from Np 6 d x2-y2 and 7 s AOs, and the corresponding unoccupied 4 b 1u * antibonding orbitals from coaxial Np 6 d x2-y2 are also hybridized with 7 s AOs. With similarity of the electronic structures, in the 13 A g state of Bk 2 O 2 the 3 a g HOMO and 4 b 1u LUMO are, as expected, composed of the 7 s/6 d hybrid AOs from two Bk atoms. For the 11 B 1u state of Cf 2 O 2 , the filled 4 a g MO is also the HOMO of the molecule and consists of 82 % 7 s and 10 % 6 d AOs.…”

“…[10] In this bonding model, 6 d orbitals take part in bonding with ligands and 5 f orbitals mainly keep non-bonding electrons. [11] This scenario could explain the chemical bonding in actinyl coordination complexes of organic ligands, such as AnO 2 (18-crown-6) [12] and UO 2 (12-thio-crown-4), [13] which could also exist in low-valence actinide compounds, especially in americium(II) compounds with negligible 5 f orbitals involving in chemical bonding. In addition, the participant of f orbitals in chemical bonding has been observed to be able to direct the compound structure.…”

Destruction of the Uranyl Moiety in a U(V) “Cation–Cation” Interaction

“…14 As a result, crown ethers have potential for actinide partitioning from nuclear waste, [15][16] particularly via size-specificity. [17][18][19][20] Gas-phase actinide crown ether complexes, including of uranyl, present a means to elucidate factors that affect complexation and coordination, including geometric effects that may be supported by distinctive crown geometries. 18,20 In the present work we extend this general line of inquiry from mononuclear uranyl-crown complexes to dimeric uranyl complexes, with an aim to understand how crown ethers might act as bridging ligands and support novel bonding motifs such as cation-cation interactions.…”

New theoretical insights into high-coordination-number complexes in actinides-centered borane

“…Furthermore, the reduced 5f energy levels as well as the increasing orbital interaction between B 2pz and An 5f orbitals when traversing the actinide series from Th to Cm consequently, reveals the An-B bonds generally transit from strengthening to weakening at An = U, which has been a general trend in actinide chemistry emerging in accordance with the atomic number of the actinides. [64][65][66][67] Besides, the net consequence of these orbital interactions upon formation of the An(BH)24 complex can be basically viewed as the An valence orbitals being destabilized energetically in Fig. 8, leading to An cations in the complexes.…”