Bonding trends across the series of tricarbonato-actinyl anions [(AnO₂)(CO₃)₃]⁴⁻ (An = U–Cm): the plutonium turn

Abstract

Actinyl-tricarbonato anions [(AnO)(CO)] (An = U-Cm) in various environments were investigated using theoretical approaches of quantum-mechanics, molecular-mechanics and cluster-models. Cations and solvent molecules in the 2 coordination sphere affect the equatorial An←O bonds more than the axial An[triple bond, length as m-dash]O bonds. Common actinide contraction is found for calculated and experimental axial bond lengths of U toPu, though no longer for Pu toCm. The tendency of U to Pu forming actinyl(vi) species dwindles away toward Cm, which already features the preferred An/Ln oxidation state of the later actinides and all lanthanides. The well known change from d-type to typical U-Pu-Cm type and then to f-type behavior is labeled as the plutonium turn, a phenomenon that is caused by f-orbital energy-decrease and f-orbital localization with increase of both nuclear charge and oxidation state, and a non-linear variation of effective f-electron population across the actinide series. Both orbital and configuration mixing and occupation of antibonding 5f type orbitals increase, weakening the AnO bonds and reducing the highest possible oxidation states of the later actinides.

Periodic Trends in Actinyl Thio-Crown Ether Complexes

“…Actinyl complexes normally coordinate 4-6 monodentate ligands in their equatorial plane. [20][21][22][23][24] The f-elements, in contrast to many d-block transition metals, are in general hard acids and therefore have a strong affinity for hard O-and F-donor ligands. The choice of donor atoms has been a hot topic in the rational design of actinide separation or sequestering ligands.…”

Transuranic Computational Chemistry

“…As econd 2016 study saw Dutkiewicz et al report further new organo-neptunium complexes, this time based on the flexible macrocyclic trans-calix [2]benzene [2]pyrrolide (L 2À ) ligand. [17] An important feature of this ligand is its ability to coordinate to metal centres in ab is(h 6 -arene) motif, highly unusual in organoactinide chemistry.R eaction of 1.5 equivalents of K 2 Lw ith NpCl 4 in THF yielded the Np III complex LNpCl, the spontaneous reduction providing an excellent entry into organo-Np III chemistry.F urthermore, equimolar reaction in THF led to the dimeric LNp 2 Cl 4 (THF) 3 .B oth new compounds were characterized crystallographically,a nd are shown schematically in Figure 5; the h 6 -arene:k 1 -pyrrolide binding mode is also observed for the isotypic monomeric Sm III [18] and U III complexes.…”

“…The linear dioxo actinyl unit {O yl -An-O yl } n + is very widely studied, in partb ecause, in its dicationic form, it is so ubiquitous in the chemistry of uranium.L iu et al recently studied computationally,u sing DFTand CASSCF methods, the electronic structure and bondingi n[ (AnO 2 )(CO 3 ) 3 ] 4À (An = U-Cm). [2] These systems feature the actinyl unit coordinated in the equatorial plane by three carbonato ligands, and were studied as highsymmetry D 3h structures. One of the main aims of the work was to rationalize the failure to prepare the Cm VI system experimentally.A nalysis of their data lead the authors to propose the concept of the "plutonium turn" in the actinides eries;t he change-over from d-bonding to d-f-bonding andt of -filling with d-bonding.…”

“…LNpCl,L Np 2 Cl 4 (THF)3 and [K(DME) n {(l -H Np(OCH 3 )}] 2 (L = trans-calix[2]benzene[2]pyrrolide).Adapted from reference[17].…”

PrB7−: A Praseodymium‐Doped Boron Cluster with a PrII Center Coordinated by a Doubly Aromatic Planar η7‐B73− Ligand

“…low-oxidation state f-element complexes is due to the more penetrating and diffuse feature of the radial probability distribution of the ns orbitals. [34] Theenergy gap between the two lowest 4f 2 6s 1 and 4f 3 states (a and e in Table S1) is calculated to be 9.44 kcal mol À1 at the PBE/TZP level or 13.59 kcal mol À1 at the CCSD(T) level. TheVDE 1 and ADE computed at two levels of theory are compared with the measured value in Table S2.…”