Binuclear Uranium(VI) Complexes with a “Pacman” Expanded Porphyrin: Computational Evidence for Highly Unusual Bis‐Actinyl Structures

On the basis of uranyl complexes reacting with a polypyrrolic ligand (H₄L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO₂)₂(L)], in which two uranyl groups were initially placed into the pacman ligand cavity, led to two minimum‐energy structures. These complexes with cation–cation interactions (CCI) exhibit unusual coordination modes of uranyls: one is a T‐shaped ( T ) skeleton formed by two linear uranyls {O_exo?U₂?O_endo→U₁(?O_exo)₂}, and another is a butterfly‐like ( B ) unit with one linear uranyl coordinating side‐by‐side to a second cis‐uranyl. The CCI in T was confirmed by the calculated longest distance and lowest stretching vibrational frequency of U₂?O_endo among the four U?O bonds. Isomer B is more stable than T , for which experimental tetrameric analogues are known. The formation of B and T complexes from the mononuclear [(UO₂)(H₂L)(thf)] ( M ) was found to be endothermic. The further protonation and dehydration of B and T are thermodynamically favorable. As a possible product, we have found a trianglelike binuclear uranium(VI) complex having a O?U?O?U?O unit.     

Infrared spectra and structure of tetravalent uranium chloride nanoclusters in electron-donor solvents

We have studied the IR absorption spectra of tetravalent uranium chlorides in electron-donor solvents. We discuss the changes in these spectra on coordination of the solvent molecules to the tetravalent uranium. We consider the participation of water molecules in this process. On this basis, we draw the conclusion that clusters form with coordination number equal mainly to six. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 729–732, September–October, 2008.     

ChemInform Abstract: From 1∞ [(UO2)2O(MoO4)4]6‐ to 1∞ [(UO2)2(MoO4)3(MoO5)] 6‐ Infinite Chains in A6U2Mo4O21 (A: Na,K, Rb,Cs) Compounds: Synthesis and Crystal Structure of Cs6 [(UO2)2(MoO4)3(MoO5)] .

Single crystals of the title compound are obtained from a melt of U₃O₈, MoO₃, and excess Cs₂CO₃ (Pt crucible, 950 °C, 12 h, cooling rate 5 °C/h).     

[U(CO3)3(H2O)2]·2H2O配合物的合成及晶体结构

A uranylcontaining compound [U(CO₃)₃(H₂O)₂]·2H₂O has been synthesized under hydrothermal condition and characterized by X-ray single-crystal analysis. Crystal structural analysis indicates that this compound consists of three CO₃^2- molecules, one U⁶⁺. The results reveal that the title compound presents a 3D frame work built up by O-H…O week hydrogen bonds interactions. The central uranium atom is eight-coordinated through three CO₃^2- molecules and two H₂O. The compound shows a coplanar hexagonal network structure, each hexagon containing a hexagonal hole with a water moleculet. CCDC: 737313.     

[U(CO_3)_3(H_2O)_2]·2H_2O配合物的合成及晶体结构

A uranylcontaining compound [U(CO_3)_3(H_2O)_2]·2H_2O has been synthesized under hydrothermal condition and characterized by X-ray single-crystal analysis. Crystal structural analysis indicates that this compound consists of three CO_3~(2-) molecules, one U~(6+). The results reveal that the title compound presents a 3D frame work built up by O-H……O week hydrogen bonds interactions. The central uranium atom is eight-coordinated through three CO_3~(2-) molecules and two H_2O. The compound shows a coplanar hexagonal network structure, each hexagon containing a hexagonal hole with a water moleculet.     

The Effect of the Equatorial Environment on Oxo‐Group Silylation of the Uranyl Dication: A Computational Study

A theoretical investigation of the reductive oxo‐group silylation reaction of the uranyl dication held in a Pacman macrocylic environment has been carried out. The effect of the modeling of the Pacman ligand on the reaction profiles is found to be important, with the dipotassiation of a single oxo group identified as a key component in promoting the reaction between the Si? X and uranium–oxo bonds. This reductive silylation reaction is also proposed to occur in an aqueous environment but was found not to operate on bare ions; in this latter case, substitution of a ligand in the equatorial plane was the most likely reaction. These results demonstrate the importance of the presence but not the identity of the equatorial ligands upon the silylation of the uranyl U? O bond.     

Electronic spectra of uranium tetrachloride clusters with electron-donor ligands

Electronic absorption spectra of nanoclusters of uranium tetrachloride are obtained experimentally and analyzed over a wide spectral range, from the visible to the IR. The structure of the long wavelength electronic absorption spectra is discussed in terms of the structure and electron-donor number of the attached ligand. Molecules of dimethyl sulfoxide (DMSO), hexamethyl phosphotriamide (HMPT), and water were used as ligands. The effect of the symmetry of the surroundings of the U⁴⁺ ion on the structure of the electronic spectrum is examined. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 182–187, March–April 2009.     

Quantum electrodynamic effects in atomic structure

Summary In high-Z atoms, quantum electrodynamic (QED) corrections are an important component in the theoretical prediction of atomic energy levels. The main QED effects in electronic atoms are the one-electron self-energy and vacuum-polarization corrections which are well known. At the next level of precision, estimates of the effect of electron interactions on the self energy and higher-order effects in two exchanged photon corrections are necessary. These corrections can be evaluated within the framework of QED in the bound interaction picture. For high-Z few-electron atoms, this approach provides a rapidly converging series in 1/Z for the corrections, which is the generalization of the well-known relativistic 1/Z expansion methods. This paper describes recent work on the effect of electron interactions on the self energy. The QED effects are particularly important for the theory for lithiumlike uranium where an accurate measurement of the Lamb shift has been made, as well as for numerous other cases where systematic differences appear between theory that does not include these QED effects and experiment.     

Isolation of Elusive HAsAsH in a Crystalline Diuranium(IV) Complex

The HAsAsH molecule has hitherto only been proposed tentatively as a short‐lived species generated in electrochemical or microwave‐plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(Tren^TIPS)}₂(μ‐η²:η²‐As₂H₂)] ( 3 , Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃; Prⁱ=CH(CH₃)₂). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back‐bonding‐type interactions from uranium to the HAsAsH π*‐orbital. This experimentally confirms the theoretically predicted excellent π‐acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane‐1,2‐diide form.