The First Uranyl Arsonates Featuring Heterometallic Cation–Cation Interactions with U^VIO–Zn^II Bonding

Two new uranyl arsonates, Zn­(UO₂)­(PhAsO₃)₂L·H₂O [L = 1,10-phenanthroline (<b>1</b>) and 2,2′-bipyridine (<b>2</b>)], have been synthesized by hydrothermal reactions of phenylarsonic acid, L, and ZnUO₂(OAc)₄·7H₂O. Single-crystal X-ray analyses demonstrate that these two compounds are isostructural and exhibit one-dimensional chains in which U^VI and Zn^II cations are directly connected by the <i>yl</i> oxygen atoms and additionally bridged by arsonate groups. Both compounds represent the first examples of uranyl arsonates with heterometallic cation–cation interactions

Weak Bimetal Coupling-Assisted MN₄ Catalyst for Enhanced Carbon Dioxide Reduction Reaction

The design of multimetal catalysts holds immense significance for efficient CO2 capture and its conversion into economically valuable chemicals. Herein, heterobimetallic catalysts (MiMo)L were exploited for the CO2 reduction reactions (CO2RR) using relativistic density functional theory (DFT). The octadentate Pacman-like polypyrrolic ligand (H4L) accommodates two metal ions (Mo, W, Nd, and U) inside (Mi) and outside (Mo) its month, rendering a weak bimetal coupling-assisted MN4 catalytically active site. Adsorption reactions have access to energetically stable coordination modes of –OCO, –OOC, and –(OCO)2, where the donor atom(s) are marked in bold. Among all of the species, (UiMoo)L releases the most energy. Along CO2RR, it favors to produce CO. The high-efficiency CO2 reduction is attributed to the size matching of U with the ligand mouth and the effective manipulation of the electron density of both ligand and bimetals. The mechanism in which heterobimetals synergetically capture and reduce CO2 has been postulated. This establishes a reference in elaborating on the complicated heterogeneous catalysis

Highly Valence-Diversified Binuclear Uranium Complexes of a Schiff-Base Polypyrrolic Macrocycle: Prediction of Unusual Structures, Electronic Properties, and Formation Reactions

On the basis of relativistic density functional theory calculations, homo- and heterovalent binuclear uranium complexes of a polypyrrolic macrocycle in a U–O–U bridging fashion have been investigated. These complexes show a variety of oxidation states for uranium ranging from III to VI, which have been confirmed by the calculated electron-spin density on each metal center. An equatorially 5-fold uranyl coordination mode is suitable for hexavalent uranium complexes, while silylation of the uranyl oxo is favored by pentavalent uranium. Uranyl oxo ligands are not required anymore for the coordination environment of tetra- and trivalent uranium because of their replacement by strong donors such as tetrahydrofuran and iodine. Optimization of binuclear U^VI–U^III complexes with various coordinating modes of U^III, donor numbers, and donor types reveals that 0.5–1.0 electron has been transferred from U^III to U^VI. Consequently, U^V–U^IV complexes are more favorable. Electronic structures and formation reactions of several representative uranium complexes were calculated. For example, a 5f-based σ­(U–U) bonding orbital is found in the diuranium­(IV) complex, rationalizing the fact that it shows the shortest U–U distance (3.82 Å) among the studied binuclear complexes

Interfacial Interaction of Titania Nanoparticles and Ligated Uranyl Species: A Relativistic DFT Investigation

To understand interfacial behavior of actinides adsorbed onto mineral surfaces and unravel their structure–property relationship, the structures, electronic properties, and energetics of various ligated uranyl species adsorbed onto TiO₂ surface nanoparticle clusters (SNCs) were examined using relativistic density functional theory. Rutile (110) and anatase (101) titania surfaces, experimentally known to be stable, were fully optimized. For the former, models studied include clean and water-free Ti₂₇O₆₄H₂₀ (<b>dry</b>), partially hydrated (Ti₂₇O₆₄H₂₀)­(H₂O)₈ (<b>sol</b>) and proton-saturated [(Ti₂₇O₆₄H₂₀)­(H₂O)₈(H)₂]²⁺ (<b>sat</b>), while defect-free and defected anatase SNCs involving more than 38 TiO₂ units were considered. The aquouranyl sorption onto rutile SNCs is energetically preferred, with interaction energies of −8.54, −10.36, and −2.39 eV, respectively. Energy decomposition demonstrates that the sorption is dominated by orbital attractive interactions and modified by steric effects. Greater hydrogen-bonding involvement leads to increased orbital interactions (i.e., more negative energy) from <b>dry</b> to <b>sol/sat</b> complexes, while much larger steric interaction in the <b>sat</b> complex significantly reduces the sorption interaction (i.e., more positive energy). For <b>dry</b> SNC, adsorbates were varied from aquo to aquo-carbonato, to carbonato, to hydroxo uranyl species. Longer U–O_surf/U–Ti distances and more positive sorption energies were calculated upon introducing carbonato and hydroxo ligands, indicative of weaker uranyl sorption onto the substrate. This is consistent with experimental observations that the uranyl sorption rate decreases upon raising solution pH value or adding carbon dioxide. Anatase SNCs adsorbing aquouranyl are even more exothermic, because more bonds are formed than in the case of rutile. Moreover, the anatase sorption can be tuned by surface defects as well as its Ti and O stoichiometry. All the aquouranyl–SNC complexes show similar character of molecular orbitals and energetic order although differing in highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps and orbital energy levels, but changes can be accomplished by adding carbonato and hydroxo ligands

The First Uranyl Arsonates Featuring Heterometallic Cation–Cation Interactions with U^VIO–Zn^II Bonding

Two new uranyl arsonates, Zn­(UO₂)­(PhAsO₃)₂L·H₂O [L = 1,10-phenanthroline (<b>1</b>) and 2,2′-bipyridine (<b>2</b>)], have been synthesized by hydrothermal reactions of phenylarsonic acid, L, and ZnUO₂(OAc)₄·7H₂O. Single-crystal X-ray analyses demonstrate that these two compounds are isostructural and exhibit one-dimensional chains in which U^VI and Zn^II cations are directly connected by the <i>yl</i> oxygen atoms and additionally bridged by arsonate groups. Both compounds represent the first examples of uranyl arsonates with heterometallic cation–cation interactions

Electron-Transfer-Enhanced Cation–Cation Interactions in Homo- and Heterobimetallic Actinide Complexes: A Relativistic Density Functional Theory Study

To provide deep insight into cation–cation interactions (CCIs) involving hexavalent actinyl species that are major components in spent nuclear fuel and pose important implications for the effective removal of radiotoxic pollutants in the environment, a series of homo- and heterobimetallic actinide complexes supported by cyclopentadienyl (Cp) and polypyrrolic macrocycle (H₄L) ligands were systematically investigated using relativistic density functional theory. The metal sort in both parts of (THF)­(H₂L)­(OAn^VIO) and (An′)^IIICp₃ from U to Np to Pu, as well as the substituent bonding to Cp from electron-donating Me to H to electron-withdrawing Cl, SiH₃, and SiMe₃, was changed. Over 0.70 electrons are unraveled to transfer from the electron-rich U^III to the electron-deficient An^VI of the actinyl moiety, leading to a more stable An^V–U^IV isomer; in contrast, uranylneptunium and uranylplutonium complexes behave as electron-resonance structures between VI–III and V–IV. These were further corroborated by geometrical and electronic structures. The energies of CCIs (i.e., O_exo–An′ bonds) were calculated to be −19.6 to −41.2 kcal/mol, affording those of OUO–Np (−23.9 kcal/mol) and OUO–Pu (−19.6 kcal/mol) with less electron transfer (ET) right at the low limit. Topological analyses of the electron density at the O_exo–An′ bond critical points demonstrate that the CCIs are ET or dative bonds in nature. A positive correlation has been built between the CCIs’ strength and corresponding ET amount. It is concluded that the CCIs of O_exo–An′ are driven by the electrostatic attraction between the actinyl oxo atom (negative) and the actinide ion (positive) and enhanced by their ET. Finally, experimental syntheses of (THF)­(H₂L)­(OU^VIO)­(An′)^IIICp₃ (An′ = U and Np) were well reproduced by thermodynamic calculations that yielded negative free energies in a tetrahydrofuran solution but a positive one for their uranylplutonium analogue, which was synthetically inaccessible. So, our thermodynamics would provide implications for the synthetic possibility of other theoretically designed bimetallic actinide complexes

Highly Diverse Bonding between Two U³⁺ Ions When Ligated by a Flexible Polypyrrolic Macrocycle

A Schiff-base polypyrrolic ligand (H₄L) can accommodate two U³⁺ ions and form a Pacman-like complex [U₂(L)]²⁺ according to relativistic density functional theory. Sixteen species, featuring four structural models in four electronic states, are energetically stable. Ligand flexibility, lack of axial restriction, and suitable U–N interactions allow the two U³⁺ ions to stretch freely over a wide range, in contrast to U₂@C_<i>n</i> (<i>n</i> = 60, 74, 80) studied previously. Diverse U³⁺–U³⁺ interactions are found. The quintet state of the Out–In model, which is calculated to be the global ground state both including and excluding the spin–orbit coupling energy, likely shows a weak single U₂ bond. In both <i>vertical</i> and <i>tilt</i> In–In species, a triple bond is found. It is composed of two two-electron–two-center bonds and two one-electron–two-center bonds; moreover, the <i>tilt</i> conformer is almost isoenergetic with Out–In. The Out–Out species shows no U···U bonding. Comparison with explicitly THF-solvated diuranium complexes is also addressed

Structural Variations of the First Family of Heterometallic Uranyl Carboxyphosphinate Assemblies by Synergy between Carboxyphosphinate and Imidazole Ligands

Hydrothermal reactions of uranyl acetate and a series of transition metal acetates with a carboxyphosphinate and auxiliary N-donor ligands gave rise to the formation of eight heterometallic uranyl-organic assemblies, namely, Co­(im)₂(UO₂)₃(L)₄ (<b>1</b>), Zn­(bpi)­(UO₂)­(L)₂ (<b>2</b>), Cd­(dib)­(UO₂)­(L)₂ (<b>3</b>), M­(dib)­(UO₂)₂(L)₃ (M = Cd (<b>4</b>), Mn (<b>5</b>)), and [M­(dib)₂(H₂O)₂]­[(UO₂)₃(L)₄]·nH₂O (M = Co (<b>6</b>, n = 2), Ni (<b>7</b>, n = 2), Cu (<b>8</b>, n = 0)) [H₂L = (2-carboxyethyl)­(phenyl)­phosphinic acid (CPP), im = imidazole, bpi =1-(biphenyl-4-yl)-1H-imidazole, dib =1,4-di­(1H-imidazol-1-yl)­benzene]. Single-crystal X-ray diffraction (XRD) analysis of <b>1</b> reveals a layered structure of UO₆, UO₇, and CoO₄N₂ units that are linked by the carboxyphosphinate ligands. Imidazole molecules modify the layer by coordinating to Co centers. Similarly, <b>2</b> is a mixed zinc-uranyl carboxyphosphinate with different topological two-dimensional structure and the decorated moiety is a bpi coligand. When in the presence of bridging dib coligands, the mixed cadmium–uranyl carboxyphosphinate sheets of <b>3</b> are pillared by dib forming a framework structure. The isostructures of <b>4</b> and <b>5</b> are also pillared frameworks constructed by a mixed heterometallic uranyl phosphinate layered subnet that is different from that of <b>3</b>. The structures of <b>6</b>–<b>8</b> are isotype and very special in that they consist of distinct [M­(dib)₂(H₂O)₂]_n²ⁿ⁺ cationic and [(UO₂)₃(L)₄]_n^2n– anionic subnets. Such two sheets are packed alternatively and interact via hydrogen bond forming three-dimensional supramolecular structures

Self-Assembly of Hierarchically Structured Cellulose@ZnO Composite in Solid–Liquid Homogeneous Phase: Synthesis, DFT Calculations, and Enhanced Antibacterial Activities

To explore the interactions of nanoparticles and bioresources and elucidate their effects on the morphology of the resulting composite, hierarchically structured cellulose@ZnO composites have been synthesized by an environmentally friendly hydrothermal method in one step. First, self-assembly induces the formation of hierarchical three-level structures, including cellulose/ZnO nanofibers, layers, and microfibers. Then, ZnO microparticles deposit onto the surface of the third-level cellulose/ZnO microfibers and accomplish the fabrication of a cellulose@ZnO composite, which eventually defines the hierarchical morphology of synthesized materials. The self-assembly mechanism was comprehensively examined. The electrostatic attraction between cellulose and ZnO, not hydrogen bonding, was found to be the main driving force for the formation of the first-level structure. A density functional theory study was conducted to support the self-assembly mechanism by optimizing the cellulose/ZnO structures at the molecular level, computing the corresponding thermodynamic energies and examining the spectroscopic properties. A hierarchically structured cellulose@ZnO composite is found to enhance the antibacterial activities. The diameters of the inhibition zone were found to be 48.8 and 45.5 mm against the Gram-positive bacterium <i>Staphylococcus aureus</i> (<i>S. aureus</i>) and the Gram-negative bacterium <i>Escherichia coli</i> (<i>E. coli</i>), respectively. This study is expected to improve food packaging materials while utilizing our newly synthesized cellulose@ZnO composite

Theoretical Study of Structural, Spectroscopic and Reaction Properties of <i>trans</i>-<i>bis</i>(imido) Uranium(VI) Complexes

To advance the understanding of the chemical behavior of actinides, a series of <i>trans</i>-<i>bis</i>(imido) uranium­(VI) complexes, U­(NR)₂(THF)₂(<i>cis</i>-I₂) (<b>2R</b>; R = H, Me, ^<i>t</i>Bu, Cy, and Ph), U­(NR)₂(THF)₃(<i>trans</i>-I₂) (<b>3R</b>; R = H, Me, ^<i>t</i>Bu, Cy, and Ph) and U­(N^<i>t</i>Bu)₂(THF)₃(<i>cis</i>-I₂) (<b>3</b>^{<i><b>t</b></i>}<b>Bu′</b>), were investigated using relativistic density functional theory. The axial UN bonds in these complexes have partial triple bonding character. The calculated bond lengths, bond orders, and stretching vibrational frequencies reveal that the UN bonds of the <i>bis</i>-imido complexes can be tuned by the variation of their axial substituents. This has been evidenced by the analysis of electronic structures. <b>2H</b>, for instance, was calculated to show iodine-based high-lying occupied orbitals and U­(<i>f</i>)-type low-lying unoccupied orbitals. Its UN bonding orbitals, formed by U­(<i>f</i>) and N­(<i>p</i>), occur in a region of the relatively low energy. Upon varying the <i><b>axial</b></i> substituent from H to ^<i>t</i>Bu and Ph, the UN bonding orbitals of <b>2</b>^{<i><b>t</b></i>}<b>Bu</b> and <b>2Ph</b> are greatly destabilized. We further compared the UE (E = N and O) bonds of <b>2H</b> with <b>3H</b> and their uranyl analogues, to address effects of the <i><b>equatorial</b></i> tetrahydrofuran (THF) ligand and the E group. It is found that the UN bonds are slightly weaker than the UO bonds of their uranyl analogues. This is in line with the finding that <i>cis</i>-UNR₂ isomers, although energetically unfavorable, are more accessible than <i>cis</i>-UO₂ would be. It is also evident that <b>2H</b> and <b>3H</b> display lower U(NH) stretching vibrations at 740 cm^–1 than the UO at 820 cm^–1 of uranyl complexes. With the inclusion of both solvation and spin–orbit coupling, the free energies of the formation reactions of the <i>bis</i>-imido uranium complexes were calculated. The formation of the experimentally synthesized <b>3Me</b>, <b>3Ph</b>, and <b>2</b>^{<i><b>t</b></i>}<b>Bu</b> are found to be thermodynamically favorable. Finally, the absorption bands previously obtained from experimental studies were well reproduced by time-dependent density functional theory calculations