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A series of hetero-bimetallic actinide complexes of the Schiff-base polypyrrolic macrocycle (L), featuring cation-cation interactions (CCIs), were systematically investigated using relativistic density functional theory (DFT). The tetrahydrofuran (THF) solvated complex [(THF)(OUVIOUIV)(THF)(L)]2+ has high reaction free energy (ΔrG), and its replacement with electron-donating iodine promotes the reaction thermodynamics to obtain uranyl iodide [(I)(OUVIOUIV)(I)(L)]2+ (UVI-UIV). Retaining this coordination geometry, calculations have been extended to other An(IV) (An = Th, Pa, Np, Pu), i.e., for the substitution of U(IV) to obtain UVI-AnIV. As a consequence, the reaction free energy is appreciably lowered, suggesting the thermodynamic feasibility for the experimental synthesis of these bimetallic complexes. Among all UVI-AnIV, the electron-spin density and high-lying occupied orbitals of UVI-PaIV show a large extent of electron transfer from electron-rich Pa(IV) to electron-deficient U(VI), leading to a more stable UV-PaV oxidation state. Additionally, the shortest bond distance and the comparatively negative Eint of the Pa-Oendo bond suggest more positive and negative charges (Q) of Pa and endo-oxo atoms, respectively. As a result of the enhanced Pa-Oendo bond and strong CCI in UVI-PaIV along with the corresponding lowest reaction free energy among all of the optimized complexes, uranyl species is a better candidate for the experimental synthesis in the ultimate context of environmental remediation.

To date, the experimental studies on Nd-based metallofullerenes are only limited to spectroscopic characterizations. In this work, the molecular structures of Nd@C82(I,II) isomers, including the isomeric symmetry of the C cage and the position of endohedral Nd atom, as well as their unique two-dimensional (2D)-layered crystallographic packing structures were initially and unambiguously elucidated, based on the X-ray structural analyses of the cocrystals of Nd@C82(I) or Nd@C82(II) with cocrystallizing agent decapyrrylcorannulene (DPC). In the V-shaped unit cell, the endohedral Nd atom prefers a site as far away from the DPC molecules as possible because of the unevenly distributed charge on the C cage mainly related to the charge transfers from the endohedral Nd atom, cocrystallizing agent DPC, and solvent toluene molecules to the C82 cage. Apart from charge transfers, multiple C-H···π intermolecular interactions are also confirmed to play important roles both for the orientation of the C cage correlated with the preferential sites of the endohedral Nd atom and for the 2D-layered packing structures within the cocrystals. Density functional theory computations offered theoretical support for the molecular structures of Nd@C82(I,II) isomers, the valence of the endohedral Nd atom (between II+ and III+), and the global ground state, i.e., the Nd@C2v(9)-C82 isomer in the quintet state.

Due to the powerful reducing ability of the metal active site, low-valent uranium complexes show remarkable performance in activating thermodynamically stable and kinetically inert small molecules. In this work, experimentally known uranium metallocenes [Cp3U]z (z = 0 and +1) were intensively studied using relativistic density functional theory for their activation of small molecules (X = CO2, N2, CO and NO). Regardless of whether z = 0 or +1, a weak double bond was realized between uranium and NO, which is in agreement with a previous study; a weak single bond with the dative nature was assigned to other small-molecule uranium adducts. A general order for the uranium–small molecule bond strength, NO > CO > N2 > CO2, has been built, the trend being exactly the same as the computed reduction potentials. These are corroborated by energetics and experimental results that (i) analogues of the first three [Cp3U(X)] adducts were crystallographically identified but the one of [Cp3U(CO2)] was not, and (ii) much higher X gas pressure was required to synthesize [Cp3U(N2)] than for [Cp3U(CO)]. Additionally, the experimentally inaccessible CO2 adduct was rationalized using thermodynamic and kinetic calculations as well as geometric/electronic properties and bonding analyses.

To explore the innovative uranyl(V) complexes by deeply understanding their coordination stability, relativistic density functional theory calculations have been performed to investigate the experimentally reported [(py)(R2AlOUVO)(py)(H2L)] [R = Me (1), iBu (2)] and [{(py)3MOUVO}(py)(H2L)] [M = Li (3), Na (4), K (5)] and their uranyl(VI) counterparts. Structural and topological analyses along with transformation-reaction energies and redox potentials were systematically studied. Geometrical and quantum theory of atoms in molecules analyses implied a linear U-Oexo-M feature in 1-3 and a bent one in 4 and 5. The calculated free energies (ΔrG) of reactions transforming 1/2 into 3/4/5 confirmed a higher stability of the latter ones, which were further corroborated by their reduction potentials (E0). The E0 value of 5 versus uranyl(VI) is close to its experimental value, particularly in solvation with spin-orbit coupling. The highest occupied and lowest unoccupied molecular orbitals of uranyl(V) and uranyl(VI) have predominant U(5fδ) character. Compared to mononuclear uranyl(VI), the coordination of aluminum and alkali metals to uranyl exo-oxo significantly contributes to the stabilization of uranyl(V) by altering the E0 value from -1.59 to -0.85, -0.91, -1.33, -1.50, and -1.46 V, respectively. The calculation results show a more positive E0 than that of the precursor 6VI/6 without exo-oxo coordination. The calculated E0 values of 3-5 are certainly more negative than those of 1 and 2. The alkali metals were found to activate U═O bonds more easily/readily than aluminum by coordination to the exo-oxo atom. In brief, the uranyl exo-oxo cation-cation-interaction enhanced the reduction ability from its uranyl(VI) analogue and raised the stability of the UV center.

Catalysis operated on supported single metal atom is considered as one of the vital efforts for chemical and energy conversion. Despite the enormous amount of research on single transition metal (TM) enhanced graphdiyne (GDY) material, its modification with slightly depleted uranium remains unexplored. Herein, we conducted relativistic density functional theory (DFT) calculations for the accumulation of atomic uranium inside size-suitable GDY pore. The stability of graphdiyne-uranium (GDY-U) is corroborated in terms of short U–C bond distances (2.34–2.44 A), with local depletion of charge and greater U(5f)-C(p) molecular orbital overlap. The magnificent structural and electronic properties of GDY-U system qualify it for the investigation of hydrogen evolution reaction (HER). The HER performance of all exposed sites, including central metal atom and four dissimilarly coordinated acetylenic carbons has been examined and compared with that of pure GDY. As the overall HER interfacial descriptor, free energy change of the intermediate state (ΔGH∗) at the central metal surface of GDY-U was found to be most favorable (0.153 eV) amongst all sites and far superior to those of pure GDY. In addition to the uranium surface, the coordinated carbons also show improved HER activity, indicating the enhancement of the system upon metal insertion. The calculated ΔGH∗ of the GDY-U system here is comparable to some of the recently reported GDY-TM materials, suggesting that atomic uranium could be an exceptional alternative for applied common catalysts.

To advance biomass-metal oxide composite synthesis, develop its interfacial chemistry and raise its performance in applications, specifying local structures and their effects are of great importance. Herein, a facile hydrothermal route was utilized to prepare a composite of renewable cellulose and zinc oxide. Microstructures from nanoscale to atomic level were examined with electron microscopy, spectroscopic technique and relativistic density functional theory. ZnO nanoparticles uniformly grow on linear cellulose nanofiber, affording an orderly hierarchical structure in general. Chemical interfacial coupling is computationally borne out. Three types of local structures with different hydrogen locations are energetically favored; notably the hydrogen-transfer one is most possibly occurring in the composite, whose interfacial interaction is dominated by orbital attractions and interfacial strength reaches − 5.06 eV. Electronic structures of the composite rationalized experimental diffuse reflectance spectra. The influence of different hydrogen positions in composite on various properties was discussed in detail. Experimental and computational characterizations unravel local structures of a typical cellulose–ZnO composite, which show different hydrogen positions. Hydrogen-transfer isomers are found the most possibly occurring, resembling the photoanode in dye-sensitized solar cells. The interfacial nature and interaction strength as well as electronic structures are determined by hydrogen locations.

Versatile graphdiyne (GDY) substrate has been modified by numerous transition metals and resulting composites showed excellent photo/electro-catalytic performance. However, GDY materials modified by actinides that are stockpiled waste product due to large-scale use in nuclear industry, are particularly scarce and remains great challenge. To deeply understand the structural properties, GDY complexating actinyl (AnmO2)n+ (An = U, Np, Pu; m = VI, V) species with its atomistic pore was investigated by relativistic density functional theory (DFT). The GDY pore was found suitable to hold actinyl species, by forming organometallic AnC dative bonds. This chemical coupling interaction was further confirmed by quantum theory of atoms-in-molecule and electronic structure calculations. The GDY-uranyl(V), for instance, shows a π(UC) bonding HOMO, which is anticipated to improve electron transfer between ligand and metal. Orbital structures and compositions of complexes suggest their implication towards catalysis, which were further corroborated by calculations on redox potentials of GDY-actinyl complexes. Hence, our results show the potential applications of GDY complexating actinyl species towards novel catalytic surfaces. Keywords: Graphdiyne-actinyl, Electronic structures and bonding, Redox properties, Relativistic DFT calculations

Four novel polyoxouranium-based uranyl carboxylates have been constructed by using a combination of three silicon-centered carboxylate ligands and polyoxouranium building blocks. Interesting oligomerization of the uranyl groups from three types of tetrameric units in 1 and 2 to octameric [(UO2)8(μ3-OH)6(μ2-OH)2(H2O)4]8+ in 3 and ultimately infinite polyoxouranium chains in 4 was observed. The 3D structure of 2 contains two different linear tetramers, whose structures are totally different from seven types of tetranuclear motifs previously observed in uranyl carboxylates. Compound 3 displays a rare octanuclear polyoxouranium brick; it is fabricated by the association of eight uranyl units in pentagonal-bipyramidal geometry that involves the edge-sharing polyhedral connection mode, which are further linked by four isolated UO7 pentagonal bipyramids to create a complicated 3D framework. These newly synthesized hybrid materials were extensively characterized by single crystal analysis, thermogravimetric analysis (TG) and different spectroscopic techniques (IR, UV-vis, and luminescence spectroscopy), which show well-resolved characteristic "five-finger" emission of the uranyl ions under excitation at 420 nm. Relativistic density functional theory (DFT) was used to explore five model compounds that theoretically simulate experimental real compounds. Experimental spectroscopy was rationalized by electronic-structure analysis.

The specification of the local structure and clarification of interfacial interactions of biomass composites is of tremendous significance in synthesizing novel materials and advancing their performance in various demanding applications. However, it remains challenging due to the limitations of experimental techniques, particularly for the manner that biomass composites commonly have hydrogen bonds involved in the vicinity of active sites and interfaces. Herein, the cellulose/Mg(OH)2 nanocomposite has been synthesized via a simple hydrothermal approach and examined by density functional theory (DFT) calculations. The composite exhibits a layered morphology; Mg(OH)2 flakes are around 50 nm in size and well-dispersed. They either anchor onto the cellulose surface or intercalate between layers. The specific composite structure was confirmed theoretically, in line with XRD, SEM and TEM observations. The interfacial interactions were found to be hydrogen bonding. The average adsorption energy per hydroxyl group was computed to be within −0.47 and −0.26 eV for a composite model comprising three cellulose chains and a two-layered Mg(OH)2 cluster. The combined computational/experimental results allow to postulate the antibacterial mechanism of the nanocomposite.

The recognition and in-depth understanding of inverse trans influence (ITI) have successfully guided the synthesis of novel actinide complexes and enriched actinide chemistry. Those complexes, however, are mainly limited to the involvement of high-valence actinide and/or metal-ligand multiple bonds. Examples containing both low oxidation state actinide and metal-metal single bond remain rare. Herein, more than 20 actinide-transition metal (An-TM) complexes of phosphinoaryl oxide ligands have been designed in accordance with several experimentally known analogs, by changing the metal atoms (An = Th, Pa, U, Np, and Pu; and TM = Ni, Pd, and Pt), actinide oxidation states (IV and III) and metal-metal axial donor ligands (X = Me3SiO, F, Cl, Br, and I). The relativistic density functional theory study of structural (trans-An-X and cis-An-O toward An-TM), bonding (topological electron/energy density), and electronic properties reveals the order of the ITI stabilizing actinide-metal bond. Computed electron affinity (EA) values, related to the electrochemical reduction, linearly correlate with experimentally measured reduction potentials. Although the same ITI order for the ligand donors was shown as in a previous study, the correlation between electrochemical reduction and the ITI was found to be weak when the actinide atoms were changed. For most complexes, the reduction is primarily of an actinide-based mechanism with minor participation of transition metal and phosphinoaryl oxide, whereas that of thorium-nickel complexes is different.

Heterobimetallic uranium-transition metal (U-TM) complexes have abundant active centers (two metals and several ancillary ligands with various donor atoms) and possible metal-metal bonding interaction, leading to diversified electronic structures and rather complicated electronic transition types. In this regard, a comprehensive and systematic theoretical study is highly desired although challenging. In the work, density functional theory (DFT) was utilized to examine a series of uranium-group 10 metal complexes supported by bidentate phosphinoaryl oxide ligands (labeled as L). TM (Ni, Pd, and Pt), uranium oxidation state (IV and III) and axial donor (I, Br, Cl, F, Me3SiO, and vacant) were varied. Calculations demonstrate an intrinsic TM → U dative bond. The order of bond strength of U-Ni > U-Pt > U-Pd is suggested by the formal shortness ratios, quantum theory of atoms in molecule (QTAIM) data, interaction energy ( Eint), and bond orders calculated at various levels of theory. It is further evidenced by relativistic effects of heavy metal, natural orbital population and electronic spectroscopy. Regarding U-Ni complexes with different axial donors, metal-metal distances are found to be linearly correlated with QTAIM data/ Eint/bond orders. Experimental UV-vis-NIR spectra were well reproduced by time-dependent DFT calculations. Complicated visible-light absorption bands, whose understanding remains unclear for many experimentally known heterobimetallic complexes, were rationalized in the work, along with NIR bands assigned as 5f → 5f transitions.

Commonly accepted uranium oxidation states in molecular complexes are III+ to VI+. Recently, this has been extended experimentally by the synthesis of seminal U(II) complexes, Y·[U(Cp′)3] and Y·[URE] (Y = K+(2.2.2-cryptand), Cp′ = C5H4SiMe3, H3RE = (Ad,MeArOH)3mesitylene and Ad = adamantyl). Relativistic density functional theory has been applied to explore whether the uranium oxidation state (+I) is possibly accessible. Calculations show that the U(I) complex of a heterocalix[4]arene (H2L) is energetically stable. It features a 5f5-dominated electronic configuration, four δ(U–Ar)-bond orbitals and a moderate UII/UI reduction potential. Its stability and structural/bonding/energetic properties were corroborated by comparisons with theoretically designed complexes [UI(Cp′)3]2− and [UIRE]2−.

The reaction of (THF)(H2L)(UVIO2) (L is a tetra-anion of polypyrrolic macrocycle) with AnIIICp3 (Cp = cyclopentadienyl) afforded two intriguing cation–cation interaction (CCI) complexes (i.e., uranyl-Np and -U), but did not yield the uranyl−Pu analogue. To complement and extend experimental results, a scalar relativistic density functional theory has been performed on the formation reactions and various relevant properties of (THF)(A2L)(OUO)–An(CpX)3 (A = Li and H; An = Pu, Np, and U; X = Me, H, Cl, and SiMe3). Inspired by a strategy that improves uranyl precursor reactivity, we utilized (THF)(Li2L)(UVIO2) instead to gain a uranyl–Pu complex. Reaction free energy is reduced even to be negative (i.e., undergoing an exergonic process), which provides the thermodynamic possibility for experimental synthesis. This manner is further rationalized by the lithiated precursor showing the increased Li–Oendo bond, uranium oxidation ability (VI → V), and exo–oxo basicity, as well as the lithiated uranyl–Pu product ha...

To remedy the heavy metal ion (HMI) pollution, unravel the relationship of material microstructure and removal performance and clarify relevant mechanism, magnesium-aluminum layered double oxide (MgAl-LDO) has been fabricated via a template method using cellulose. The variously performed characterizations show that ultra-thin flakes of about 5 nm are successfully accessible with the size of 50 ~ 100 nm. They are smaller than the ones prepared without the addition of cellulose. The distinctive structural feature endows the newly-synthesized LDO with large removal capacity for HMIs. Towards Cd2+, Pb2+ and Cu2+, the removal capacity reaches as high as 1422.3, 1336.8 and 1135.4 mg·g−1, respectively. Moreover, the highly achieved durability makes our LDO applicable to treating the polluted water. The mechanism of cation exchange along with deposition has been postulated. The Mg-OH moiety in the sample is found to dominate the HMI removal. The experimental findings are borne out by the first-principle density functional theory calculations on geometries, thermodynamics and electronic structures.

The redox properties of actinides play a significant role in manipulating organometallic chemistry and energy/environment science, for being involved in fundamental concepts (oxidation state, bonding and reactivity), nuclear fuel cycles and contamination remediation. Herein, a series of trans-calix[2]pyrrole[2]benzene (H2L2) actinide complexes (An = Ac–Pu, and oxidation states of +II and +III) have been studied by relativistic density functional theory. Reduction potentials (E0) of [AnL2]+/[AnL2] were computed within −2.45 and −1.64 V versus Fc+/Fc in THF, comparable to experimental values of −2.50 V for [UL1e]/[UL1e]− (H3L1e = (Ad,MeArOH)3mesitylene and Ad = adamantyl) and −2.35 V for [U(CpiPr)2]+/[U(CpiPr)2] (CpiPr = C5iPr5). The E0 values show an overall increasing trend from Ac to Pu but a break point at Np being lower than adjacent elements. The arene/actinide mixed reduction mechanism is proposed, showing arenes predominant in Ac–Pa complexes but diverting to metal-centered domination in U–Pu ones. Besides being consistent with previously reported those of AnIII/AnII couples, the changing trend of our reduction potentials is corroborated by geometric data, topological analysis of bonds and electronic structures as well as additional calculations on actinide complexes ligated by tris(alkyloxide)arene, silyl-cyclopentadiene and octadentate Schiff-base polypyrrole in terms of electron affinity. The regularity would help to explore synthesis and property of novel actinide(II) complex.

A g-C

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)(OAnVIO) 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 UIII to the electron-deficient AnVI of the actinyl moiety, leading to a more stable AnV–UIV isomer; in contrast, uranylneptunium and uranylplutonium complexes behave as electron-resonance structures between VI–III and V–IV. These were further corroborated by geometrica...

Two novel three-dimensional interpenetrated uranyl–organic frameworks, (NH4)4[(UO2)4(L1)3]·6H2O (1) and [(UO2)2(H2O)2L2]·2H2O (2), where L1 = tetrakis(3-carboxyphenyl)silicon and L2 = tetrakis(4-carboxyphenyl)silicon, were synthesized by a combination of two isomeric tetrahedral silicon-centered ligands with 3-connected triangular [(UO2)(COO)3]− and 4-connected dinuclear [(UO2)2(COO)4] units, respectively. Structural analyses indicate that 1 possesses a 2-fold interpenetrating anion bor network, while 2 exhibits a 3-fold interpenetrated 4,4-connected neutral network with pts topology. Both compounds were characterized by thermogravimetric analysis and IR, UV–vis, and photoluminescence spectroscopy. A relativistic density functional theory (DFT) investigation on 10 model compounds of 1 and 2 shows good agreement of the structural parameters, stretching vibrational frequencies, and absorption with experimental results; the time-dependent DFT calculations unravel that low-energy absorption bands originate fr...

In-depth understanding of interfacial property is the key to guiding the synthesis of biomass composites with desired performance. However, the exploration is of great challenge due to limitations of experimental techniques in locating hydrogen, requiring large/good crystals and detecting a weak interaction like van der Waals (vdW). Herein, we experimentally and computationally investigated the composite cellulose/zinc oxide/g-C3N4. Hydrothermal synthesis afforded cellulose/ZnO, and then fabricated the ternary composite by adding g-C3N4 under ultrasonic condition. Three components are found to co-exist in the composite, and the ZnO nanoparticle is attaching to cellulose and coupling with g-C3N4. These experimental findings were corroborated by relativistic DFT calculations. The interfacial coupling is elaborated as contributions of dative bonds, hydrogen bonds and vdW interaction. The vdW is increased by a factor of 4.23 in the ZnO/g-C3N4 interface. This improves electron-hole separation and offers prospective application of the composite in photocatalysis, antibacteria and gas sensing.

To explore the uranium-uranium bonding nature, a ligated diuranium complex that could be experimentally possible would show features with no bridging ligand constraints (i.e. discrete or unsupported ligand), rigid ligand skeleton and suitable U-ligand bond. In this respect, we have designed and examined a series of diuranium diporphyrazines (U m 2 Pz 2 , m = II, III and IV) using relativistic density functional theory. Optimizations on all possible electron-spin isomers find that the triplet, quintet and quintet states are energetically lowest for U m 2 Pz 2 (m = II, III and IV), respectively. They possess bond lengths of U U at 2.37, 2.46 and 2.91 A, bond orders of 3.48, 3.33 and 2.11, and stretching vibrational frequencies of 239, 172 and 108 cm −1 . Associated with the electronic-structure and QTAIM (quantum theory of atoms in molecules) analyses, a weak quadruple bond is suggested for the triplet state of U II 2 Pz 2 , and the triple and double bonds for U III 2 Pz 2 , and U IV 2 Pz 2 , respectively. It shows that the uranium oxidation state approximately correlates with the number of multiple bonds.

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 (dry), partially hydrated (Ti27O64H20)(H2O)8 (sol) and proton-saturated [(Ti27O64H20)(H2O)8(H)2]2+ (sat), 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 involvemen...

The ever-growing contamination of water resources generated by heavy metals is posing significant threat to sustainable development, and urging the necessity of safe disposal. In this work, we designed a facile method to prepare carbon dots/Mg(OH)2 (marked as CDs/Mg(OH)2) composite, which enables to remove and recover potentially toxic metal of Cd2+ from water. The newly-prepared CDs/Mg(OH)2 features a hierarchical petaloid-array structure and has large specific surface area of 96.2 m2 g−1. It is evident that the composite is composed of Mg(OH)2 slices, to which CDs are attached. Density functional theory calculation recognized the composite microstructure at the atomic level. Weak chemical coupling between sub-units were borne out by optimized structures, energetics, infrared vibrations, and electronic structures. The CDs/Mg(OH)2 composite shows high removal capacity and long durability while treating Cd(II)-contaminated water. The incorporation of CDs could regulate and control the up-taking rate of Cd2+ ions and consequently fabricate well-dispersed 1D nanowires of Cd(OH)2. The corresponding mechanism was proposed. Specifically, the sample CDs/Mg(OH)2-60 reaches 1015.4 mg g−1 removal capacity; it can be used for 12 cycles and still keep removal efficiency as high as 98.6%.

Although previously studied [(HOOC)4(TBPor)Ru(NCS)2]2– (A; TBPor = tetrabenzoporphrin) avoided the intrinsic π-stacking aggregation of planar metallophorphryins via incorporating two axial ligands, these isothiocyanato groups are believed to be the weakest part of the sensitizer while operating in dye-sensitized solar cells (DSSCs). In this work, a series of thiocyanate-free ruthenium porphyrin complexes featuring with phenyl/substituted-phenyl axial groups, [(HOOC)4(TBPor)Ru(L′)2]2– (L′ = Ph (1), PhF2 (2), PhCl2 (3), PhBr2 (4), and PhI2 (5)), have been examined using density functional theory (DFT) and time-dependent DFT (TD-DFT). Both analyses of electronic structures and calculations of interaction energies demonstrate that the Ru-L′ interaction in 1–5 is significantly enhanced relative to the Ru-NCS in A, which will raise chemical stability of the former in DSSCs. Single-electron oxidation mechanism has been proposed. Oxidation potentials (E0) are increased by 0.2–0.6 V when changing axial groups from NCS to Ph/PhX2. The spin-orbit coupling (SOC) relativistic effects can be negligible in computing E0 values. TD-DFT calculations show that 1–5 have more intense Q band in the visible region than A does. Taken together, high chemical stability, suitable oxidation potential and expanding absorption spectra would allow for potential applications of the thiocyanate-free sensitizers in DSSCs. © 2016 Wiley Periodicals, Inc.

Pentavalent trans-bis(imido) uranium complexes, [UV(NR)2(THF)2(cis-I2)]− (2R), [UV(NR)2(THF)3(trans-I2)]− (3R) and [UV(NtBu)2(THF)3(cis-I2)]− (3tBu′), have been examined using relativistic density functional theory, where the R substituent is changed from CF3, Ph, H, Me, tBu to Cy. The calculated electron-spin density indicates the 5f1 configuration on the uranium center, which is mainly reflected by the HOMO with over 96% metal character. The UV N triple bond in these complexes is evidenced by computed bond length, bond order and electronic structure, although being weaker than UVI N in their hexavalent analogues and UV O in uranyl analogues. The U NH stretching vibrational frequencies of 2H and 3H are calculated between 698 and 745 cm−1, while the U N C ones of other complexes are found in the range from 1043 to 1285 cm−1. This shift is caused by the strong coupled interaction between sizable substituent and U N bond. The present study unravels that the changes of the R substituents as well as the number and the position of equatorial donors are capable of tuning structural and electronic properties of bis-imido complexes.

Relativistic density functional theory was used to explore the structural and redox properties of 18 prototypical actinyl silylamides including a variation of metals (U, Np and Pu), metal oxidation states (VI and V) and equatorial ligands. A theoretical approach associated with implicit solvation and spin–orbit/multiplet corrections was proved to be reliable. A marked shift of reduction potentials of actinyl silylamides caused by changes of equatorial coordination ligands and implicit solvation was elucidated by analyses of electronic structures and single-electron reduction mechanism.

The local electric field formed between dye sensitizers and semiconductor interface is one of key factors to determine the overall performance of dye-sensitized solar cells (DSSCs). Herein, a strategy has been proposed to explore the influence of the local electric field on the functionality of DSSCs of YD2-O-C8 dye via calculating the relevant properties in various electric field strengths. The YD2-O-C8 dye has been systemically studied with density functional theory (DFT) and time-dependent DFT (TD-DFT) for its electronic structure and optical properties in tetrahydrofuran (THF) solution. The absorption spectra are gradually narrowing and blue-shifting while increasing the electric field strength. Two key parameters of the light harvesting efficiency (LHE) and the TiO 2 conduction band shift (Δ E cb ) have been examined for the YD2-O-C8 sensitized TiO 2 system. It is found that it is of great importance to reduce the charge accumulation on the TiO 2 film, which lowers the electric field strength and shows the best performance of DSSCs. This study is expected to deepen our understanding of the function of local electric field and the operational principles of the DSSCs for further optimization.

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@Cn (n = 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 vertical and tilt 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 tilt 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 ...

Understanding of reaction and structural property of diuranium(III) complexes of a single ligand is essential to advancing their experimental synthesis and exploring promising applications in small molecule activation chemistry. In this work, we theoretically examined a series of diuranium(III) complexes building on the reaction of [UI 3 (THF) 4 ] and octadentate polypyrrolic ligands (H 4 L 1 and H 4 L 2 ). At the relativistic density functional theory level, 11.2 kcal/mol energy is required to form the Pacman-like [(UI) 2 (μ 2 -I)(L 1 )] − ( 1 ) in THF solution, while only 0.5 kcal/mol for its non-classic Pacman isomer 1n . These agree with their analogues that have been experimentally proposed. A variety of chemical modification has been made for 1 . The addition of one THF solvent or one iodine ion raises reaction energy by 6.8∼14.5 kcal/mol, while two or more are significantly endoergic. Smaller energies of 1.4 and 7.4 kcal/mol are required when varying bridged atom (from the iodine of 1 into the THF of 2 [(UI) 2 (μ 2 -THF)(L 1 )]) and lengthening ligand linker size (from ortho -phenylene of H 4 L 1 of 1 into anthracene of H 4 L 2 of 3 [(UI) 2 (μ 2 -I)(L 2 )] − ), respectively. Eleven diuranium(III) complexes were optimized to be energetically stable. The U–U distances of 4.13 and 4.08 A were calculated for 1 and 2 , respectively, compared with the long one of 5.90 A for 3 .

Uranyl complexes, [(UO 2 )(py)F 4 ] 2– ( 1a , py = pyridine), [(UO 2 )(py) 3 ( cis -F) 2 ] ( 1a′ ), [(UO 2 )(py) 5 ] 2+ ( 1a″ ), [(UO 2 )(bpy)F 3 ] – ( 2a , bpy = 2,2′-bipyridine), [(UO 2 )(tpy)F 2 ] ( 3a , tpy = 2,2′:6′2″-terpyridine) and [(UO 2 )(qpy)F] + ( 4a , qpy = 2,2′:6′,2″:6″,2‴-quaterpyridine) have been examined using scalar relativistic density functional theory (DFT). It is shown that both increasing the mono pyridyl number (from 1a to 1a′ and 1a″ ) and extending the pyridyl conjugation (from 1a to 2a , 3a and 4a ) are capable of tuning electronic structures of uranyl complexes. Unlike those of 1a , for instance, 4a is featured with π(qpy) character of HOMO and HOMO-1, and its σ(U O) bond is greatly stabilized to form HOMO-2; and more π ∗ (qpy)-type orbitals insert between U( f )-based and π ∗ (U O) unfilled orbitals. For comparison, fourfold uranyl complexes with one less equatorial fluorine ligand ([(UO 2 )(py)F 3 ] – ( 1b ), [(UO 2 )(bpy)F 2 ] ( 2b ), [(UO 2 )(tpy)F] + ( 3b ) and [(UO 2 )(qpy)] 2+ ( 4b )) were calculated. Both thermodynamic and geometrical results suggest that polypyridyl (such as bpy, tpy and qpy) dioxouranium complexes favor five-coordinated mode in the equatorial plane, whereas fourfold is preferred by the single-pyridyl complex.

A family of di-, tri-, and tetranuclear copper(I) complexes supported by length-controlled silaamidinate ligands have been synthesized to show short Cu(I)-Cu(I) distances (2.43-2.62 Å) and feature a linear or bent metal-metal arrangement, which is elucidated by a relativistic density functional theory calculation.

To understand the structural and electronic properties of uranium complexes, the cis-bis(imido)uranium iodides cis-[U(NPh)2(THF)3I2] (3Ph) and cis-[U(NPh)2(THF)2I2] (2Ph) have been designed, and their structures and properties have been calculated by density functional theory (DFT) and time-dependent DFT. Four isomers (3Ph1, 3Ph2, 2Ph1, 2Ph2) were addressed in the study; these isomers have the structural feature that one iodide atom is trans to one imido group in the axial direction, and the other iodine atom is cis to the other imido group in the equatorial plane. The total system energies, geometry parameters, and vibrational spectra were similar among the respective isomers. Analyses of the electronic structures in tetrahydrofuran solution revealed that these isomeric complexes show mixed π(U=N) and π(Ph) character for the highest occupied molecular orbital (HOMO) and HOMO–1; the lone pairs of electrons of the iodine atom are dominant in the energetically lower occupied orbitals. U(f)-type orbitals contribute to the low-lying unoccupied orbitals, as has been generally accepted for analogous hexavalent trans-dioxouranium complexes. Three main absorption peaks were observed for 3Ph1/3Ph2 and 2Ph1/2Ph2 from time-dependent long-range-corrected functional calculations. The first one originates from the π(U=N) bonds and the phenyl groups, and the third is related to character of the iodine atoms [σ(U–I) and π(I)]; combined π(I) and π(U=N) character is attributed to the middle peak. We also calculated the experimentally known trans-U(NPh)2(THF)3I2 (trans-3Ph). The comparison of trans-3Ph, 3Ph1, and 3Ph2 indicates that the cis/trans isomerism has a relatively large effect on their structural and electronic properties.

N749 has been widely investigated in the dye-sensitized solar cells (DSSCs) for its high incident photon-to-current conversion efficiency (IPCE) in the long wavelength range. Absorption spectra of the N749 –TiO 2 photoanode have been theoretically examined in this article. Depending on rational models between dye and TiO 2 film, the experimental absorption peaks have been well reproduced through density functional theory (DFT) and time-dependent DFT (TDDFT) approaches. The calculation results show that types of N749 connecting to TiO 2 electrode affect the utilization of solar energy in DSSCs. The way of electron injection can be distinguished based on the character of the interfacial charge transfer. In addition, the deprotonation of dye molecule also has a significant effect on the absorption spectrum. It is demonstrated that the dyes with closely-lying unoccupied orbitals, allowing for enhanced orbital-coupling, would improve the total photo-to-current conversion efficiency in DSSCs.

Given their efficacy in photosynthesis, a series of metalloporphyrins were examined using density functional theory (DFT) and time-dependent DFT. An experimentally known zinc porphyrin has been calculated to evaluate performance of various functionals, basis sets, computational models of solvent effect and solvent sorts. With an alternative approach, absorption spectra of complexes ( ML x , M = Zn, Cd and Hg, x = 1–4) varying substituted porphyrin L x and metal center were investigated. It was shown that the strongest peak at about 400 nm for ML x was attributed to the intra -porphyrin π → π * transition. Substitution of benzoic acid at the β -position of porphyrin core allows an extra intense peak at 450 nm in ML 3 and ML 4 , but ML 2 with the meso -substituted benzoic acid only displays some very weak low-energy absorptions. Additionally, we theoretically designed [Ru(NCS) 2 L x ] 2− and expected their possession of advantages of polypyridyl ruthenium and porphyrin-based sensitizers. The present study reveals that the L 4 complex, [Ru(NCS) 2 L 4 ] 2− , exhibits extra intense absorption peaks at 500 and 582 nm, allowing for its promising application in dye-sensitized solar cells (DSSCs).

To advance the understanding of the chemical behavior of actinides, a series of trans-bis(imido) uranium(VI) complexes, U(NR)2(THF)2(cis-I2) (2R; R = H, Me, (t)Bu, Cy, and Ph), U(NR)2(THF)3(trans-I2) (3R; R = H, Me, (t)Bu, Cy, and Ph) and U(N(t)Bu)2(THF)3(cis-I2) (3(t)Bu'), 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 bis-imido complexes can be tuned by the variation of their axial substituents. This has been evidenced by the analysis of electronic structures. 2H, for instance, was calculated to show iodine-based high-lying occupied orbitals and U(f)-type low-lying unoccupied orbitals. Its U═N bonding orbitals, formed by U(f) and N(p), occur in a region of the relatively low energy. Upon varying the axial substituent from H to (t)Bu and Ph, the U═N bonding orbitals of 2(t)Bu and 2Ph are greatly destabilized. We further compared the U═E (E = N and O) bonds of 2H with 3H and their uranyl analogues, to address effects of the equatorial 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 cis-UNR2 isomers, although energetically unfavorable, are more accessible than cis-UO2 would be. It is also evident that 2H and 3H 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 bis-imido uranium complexes were calculated. The formation of the experimentally synthesized 3Me, 3Ph, and 2(t)Bu 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.

Relativistic density functional theory was used to explore a series of bisactinyl complexes, [(phen)(AnVIO2)(μ2-F)(F)]2 (An = U (1), Np (2) and Pu (3); phen = phenanthroline; μ2 = doubly bridged), [(phen)(UVO2)(μ2-F)(F)]22− (4), [(phen)(UVIO2)(μ2-X)(X)]2 (X = Cl (5), Br (6) and I (7)), [(L)(UVIO2)(μ2-F)(F)]2 (L = bpy (8), 2NH3 (9) and 2F (10); bpy = 2,2′-bipyridine) and [NH4]4[(F)2(UVIO2)(μ2-F)(F)]2 (11). The effects of varying actinyl ions (UO22+, NpO22+ and PuO22+), oxidation states of uranium (VI and V) and equatorial ligands (phen → bpy → 2NH3 → 2F and F → Cl → Br → I) on the structures and electronic properties of complexes were examined. The calculated distances and bond orders of AnO indicate the partial triple bonding character, and agree with the trends in the AnO stretching vibrational frequencies. The free energies of formation reactions of 1–11 calculated in the aqueous solution demonstrate that 1, 8 and 11 are thermodynamically stable. In this work, we have successfully synthesized 1 and [Me2NH2]4[(F)2(UVIO2)(μ2-F)(F)]2 (12), which is represented by theoretical model complex 11. Their characterizations of the single crystal X-ray diffraction and infrared are consistent with the calculated results; the measured fine-structured fluorescent emissions were assigned as transitions from the UO bonding to the U (f) orbital by analyzing the electronic structure and absorption spectra.

Relativistic density functional theory finds that two isomers of a diuranium(III) complex of a polypyrrolic macrocycle (H4L) feature active sites on uranium moieties, allowing for their potential application in activating industrially and economically important small molecules. To address this, a series of adducts [(X)nU2(L)]((2-m)+) (X = THF, I(-) and HI; n = 1 and 2; m = 0, 1 and 2) have been examined. The coordination from X to the exposed uranium(s) changes the general geometry and electronic structure slightly. Thermodynamic calculations reveal that iodine termination is energetically favored over THF/HI coordination. Graphical abstract Scalar and spin-orbit coupling relativistic DFT calculation reveals that the active sites on the uranium moieties of [U2(L)](2+) lead to formation of adducts [(THF)nU2(L)](2+), [InU2(L)]((2-n)+) and [(HI)nU2(L)](2+) (n = 1 and 2). Coordination to the exposed uranium(s) changes geometrical and electronic properties slightly, but iodine termination is the most energetically favored.

Eighteen actinyl complexes of a Schiff-base polypyrrolic macrocycle (H4L), [(Sol)(AnmO2)(H2L)]n− (Sol = Vacant, pyridine (py) and tetrahydrofuran (THF); An=U, Np and Pu; m = VI and n = 0, m = V and n = 1) were investigated using relativistic density functional theory. Comparison of complexes with and without the explicit solvent coordination to the metal center, and changes in actinide element and metal oxidation state provide insight into their effects on structural and energetic properties of the complexes. Compared with those of the solvent-free complexes, the An=O bond lengths of the solvated complexes differ within 0.01 A, and the deviation of the O=An=O angles is less than 1°. The H···Oendo bonds are relatively sensitive to the explicit solvent coordination, showing the largest discrepancy of 0.05 A. Charges and electron-spin densities of actinides are only slightly affected by the inclusion of the explicit solvent. Reduction potentials of actinyl complexes have been addressed, and their dependence on the bulk solvent polarity is being discussed, using a simple model based on the Born equation.

The flexible small-cavity macrocycle, trans-calix[2]benzene[2]pyrrolide (H2L), has been found experimentally to complexate low-valent UIII and UIV with binding pockets (BP) of bis(arene) (Ar) and bis(pyrrolide) (Pl), respectively. This switchable coordination of the uranium center has been explored using relativistic density functional theory (DFT) in this work. Systematic calculations of [(BP-L)Anm(η-H)nBH4-n)]z+ (BP = Ar and Pl; An = U, Np and Pu; m = III and IV; n = 2 and 3; and z = 0 and 1), labeled as BP-Anm-nH, were carried out. Energetics and geometrical/electronic-structure analyses reveal that the size matching between actinide ions and the binding pocket plays a significant role in determining the energetic ordering of isomers. The relatively large-size UIII and NpIII ions are selectively preferred by the large bis(arene) pocket, yielding the most stable isomer of Ar-An-2H; simultaneously formed δ(An-Ar2) bonding helps stabilizing the system. In contrast, the small-size PuIII and AnIV are held by the smaller bis(pyrrolide) to show the energetically favored Pl-An-3H isomer. This size argument is further supported by calculations on the related Th and Pa compounds. The formation reactions of BP-Anm-nH demonstrate an endothermic process when using the H2L ligand reactant. Applying a more basic alkali ligand (A2L; A = Li, Na and K) as the reactant significantly reduces the reaction energy and presents thermodynamic possibility to prepare the low-valent actinide complexes. This is in agreement with the experimental synthesis where K2L was utilized. The redox potentials (E0) from tri- to tetravalent actinides were calculated while including both solvation and spin-orbit coupling effects. The highly reductive nature of the UIII complex was manifested by the calculated E0 of over 1.1 V.

The computationally- and experimentally-determined molecular structures of a bis-uranyl(VI) complex of an expanded Schiff-base polypyrrolic macrocycle [(UO2)2(L)] are in close agreement only if the pyridine in the fifth equatorial donor site on the uranium is included in the calculations. The relativistic density functional theory (DFT) calculations presented here are augmented from those on previously reported simpler frameworks, and demonstrate that other augmentations, such as the incorporation of condensed-phase media and the changes in the peripheral groups of the ligand, have only a slight effect. Synthetic routes to pure samples of the bis- and mono-uranyl(VI) complexes have been developed using pyridine and arene solvents, respectively, allowing the experimental determination of the molecular structures by X-ray single crystal diffraction; these agree well with the calculated structures. A comprehensive set of calculations have been performed on a series of actinyl AnO2n+ complexes of this macrocyclic ligand. These include both bis- and mono-actinyl adducts for the metals U, Np and Pu, and formal oxidation states VI and V. The reduction potentials of the complexes for U, Np, and Pu, incorporating both solvation and spin-orbit coupling considerations, show the order Np > Pu > U. The agreement between experimental and computed data for U is excellent, suggesting that at this level of computation predictions made about the significantly more radiotoxic Np and Pu molecules should be accurate. A particularly unusual structure of the mononuclear plutonyl(V) complex was predicted by quantum chemical calculations, in which a twist in the macrocycle allows one of the two endo-oxo groups to form a hydrogen bond to one pyrrole group of the opposite side of the macrocycle, in accordance with this member of the set containing the most Lewis basic oxo groups.

Two 3D uranyl organic frameworks (UOFs) with entangled structures, (HPhen)2[(UO2)2L2]·4.5H2O (1) and [(UO2)3(H2O)4L2]·6H2O (2), were synthesized using a rigid tripodal linker (4,4′,4″-(phenylsilanetriyl)tribenzoic acid, H3L). Compound 1 represents a 2-fold interpenetrating UOF with the unique (10,3)-b topology. Compound 2 is composed of three interlocked sets of identical singlet networks and thus exhibits a rare 3D polythreading network with (3,4)-connected topology. These two compounds have been characterized by IR, UV–vis, and photoluminescent spectroscopy. A density functional theory (DFT) study on the model compounds of 1 and 2 shows good agreement of structural parameters and U═O stretching vibrational frequencies with experimental data. The experimentally measured absorption bands were well reproduced by the time-dependent DFT calculations.

Electron injection from a photoexcited chromophore into the surface of mesoscopic semiconductor TiO 2 nanoparticles is one of the key electron transfer processes for DSSC. A reasonable and reliable TiO 2 surface model (dropped down the anatase (101) and rutile (110) crystals a slab model) was designed, which was employed to investigate the absorption behavior of the adsorbed dye molecules such as C101 , J13 and N749 under DFT method. According to the calculation results, the detailed orbital components and absorption transition are obtained; furthermore, the ultrafast, excited-state electron injection and emission electron injection can be discriminated. Generally, both the connecting surfaces of TiO 2 and degree of deprotonating dye molecules could influence absorption spectrum intensely. Our calculations show that the more efficient DSSCs should have larger conjugation degree for ancillary ligands or the whole system, which is beneficial to photon absorption from the visible to near-IR region.

A series of dye molecules was designed theoretically. Particularly, azoles and their derivatives were cho- sen as the modifying groups linking to ancillary ligands of (Ru(dcbpyH2)2(NCS)2)(N3, dcbpy=4,4'-dicarboxy- 2,2'-bipyridine; NCS=thiocyanato). Density functional theory(DFT) based approaches were applied to exploring the electronic structures and properties of all these systems. The dye molecule with 1,2,4-triazole groups which exhibits a very high intensity of absorption in visible region, was obtained. Time-dependent DFT(TD-DFT) results indicate that the ancillary ligand dominates the molecular orbital(MO) energy levels and masters the absorption transition nature to a certain extent. The deprotonation of anchoring ligand not only affects the frontier MO energy levels but also con- trols the energy gaps of the highest occupied MO(HOMO) to the lowest unoccupied MO(LUMO) and LUMO to LUMO+1 orbital. If the gap between LUMO-LUMO+1 is small enough, the higher efficiency of dye-sensitized solar cell(DSSC) should be expected. Keywords Dye-sensitized solar cell; Density functional theory(DFT); Frontier molecular orbital; Absorption spectrum; Deprotonation Article ID 1005-9040(2012)-04-696-07

The density functional theory (DFT) was applied to fully optimize the ground- and excited-state structures of six ruthenium photosensitizers with 0–4 carboxyls coordinating phenanthroline ligands. The electronic spectra in solution were calculated by the time-dependent DFT (TD-DFT) method. The results showed that all the carboxylic sensitizers are good candidates for dye-sensitized solar cell because of their intense and wide absorption bands in the visible region. Varying carboxyl groups of the sensitizers slightly changes the absorption spectra, but the number and substituted position of these anchors strongly improve the electron-accepted ability of their situated phenanthrolines.

A series of heterobimetallic d10−d8 complexes, [AuIM′(R1)2(R2)2] (M′ = PtII, AuIII; R1 = CN−, C≡CH−; R2 = PH2CH2PH2, CH2PH2CH2−), were explored using ab initio methods and time-dependent density functional theory (TD-DFT). In the ground states, d10−d8 distances were calculated at 2.88−3.00 A with associated vibrational frequencies of 102−114 cm−1 by the MP2 method; energies of metallophilic interactions were estimated to be in the range 11.0−18.2 and 7.03−9.14 kcal/mol at the MP2 and CCSD levels, respectively. With the reference complex [AuIPtII(CN)2(PH2CH2PH2)2]+ (1), the variation of the d8 heterometal (M′), the coordination environment of the d8 metal (R1), and the bridging ligand (R2) changes the electronic structures and thus further tunes the electronic spectroscopy of these complexes. The known experimental absorption spectra were well reproduced by the present TD-DFT calculations. Upon excitation, UMP2 revealed the metal−metal interactions in their triplet excited states were strengthened. The cor...

On the basis of uranyl complexes reacting with a polypyrrolic ligand (H(4)L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO(2))(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)=U(2)=O(endo)-->U(1)(=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 U(2)=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 [(UO(2))(H(2)L)(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.

The electronic properties of R C C H (1), [R C C HgCH3] (2), [CH3Hg C C R C C HgCH3] (3) and [R C C Hg C C R] (4) (R = fluoren-9-one) in the ground and singlet/triplet excited states were explored theoretically. Calculations indicate that geometry parameters of 1–4 change slightly on going from ground state to excited state. Experimental spectra were well reproduced by the combined TD-DFT (time-dependent density functional theory) and PCM (Polarized-Continuum Model) calculations. With increasing methylmercury and/or fluorenone groups, the featured absorption and emission bands of complexes are redshifted. The investigation reveals such a variation can tune excitation energies but not change transition nature.

To understand their photocatalytic activity and application in luminescent materials, a series of gold and rhodium phosphine complexes (mononuclear [Au(I)(PH(3))(2)](+) (1) and [Rh(I)(CNH)(2)(PH(3))(2)](+) (2); homobinuclear [Au(I)(2)(PH(2)CH(2)PH(2))(2)](2+) (3) and [Rh(I)(2)(CNH)(4)(PH(2)CH(2)PH(2))(2)](2+) (4); heterobinuclear [Au(I)Rh(I)(CNH)(2)(PH(2)CH(2)PH(2))(2)](2+) (5), [Au(I)Rh(I)(CNH)(2)(PH(2)NHPH(2))(2)Cl(2)] (6), and [Au(I)Rh(I)(CNH)(2)(PH(2)NHPH(2))(2)](2+) (7); and oxidized derivatives [Au(II)Rh(II)(CNH)(2)(PH(2)CH(2)PH(2))(2)](4+) (8), [Au(II)Rh(II)(CNH)(2)(PH(2)NHPH(2))(2)Cl(3)](+) (9), and [Au(II)Rh(II)(CNH)(2)(PH(2)NHPH(2))(2)](4+) (10)) were investigated using ab initio methods and density functional theory. With the use of the MP2 method, the M-M' distances in 3-7 were estimated to be in the range of 2.76-3.02 A, implying the existence of weak metal-metal interaction. This is further evident in the stretching frequencies and bond orders of M-M'. The two-electron oxidation from 5-7 to their respective partners 8-10 was shown to mainly occur in the gold-rhodium centers. Experimental absorption spectra were well reproduced by our time-dependent density functional theory calculations. The metal-metal interaction results in a large shift of d(z(2)) --p(z) transition absorptions in binuclear complexes relative to mononuclear analogues and concomitantly produces a low-lying excited state that is responsible for increasing visible-light photocatalytic activities. Upon excitation, the metal-centered transition and the metal-to-metal charge transfer strengthen the metal-metal interaction in triplet excited states for 3-6, while the promotion of electrons into the sigma*(d(z(2))) orbital weakens the interaction in 9.

The geometries, electronic structures, and spectroscopic properties of Ir(ppy)2(N^N)+ (1) (N^N = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline, ppy = 2-phenylpyridine), Ir(ppy)2(N^N)+·F− (2), Ir(p...

The ground- and excited-state structures for a series of Os(II) diimine complexes [Os(N ∧ N)(CO) 2 I 2 ] (N ∧ N = 2,2′-bipyridine (bpy) ( 1 ), 4,4′-di- tert -butyl-2,2′-bipyridine (dbubpy) ( 2 ), and 4,4′-dichlorine-2,2′-bipyridine (dclbpy) ( 3 )) were optimized by the MP2 and CIS methods, respectively. The spectroscopic properties in dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model. It was shown that the lowest-energy absorptions at 488, 469 and 539 nm for 1 – 3 , respectively, were attributed to the admixture of the [d xy (Os) → π ∗ (bpy)] (metal-to-ligand charge transfer, MLCT) and [p(I) → π ∗ (bpy)] (interligand charge transfer, LLCT) transitions; their lowest-energy phosphorescent emissions at 610, 537 and 687 nm also have the 3 MLCT/ 3 LLCT transition characters. These results agree well with the experimental reports. The present investigation revealed that the variation of the substituents from H → t -Bu → Cl on the bipyridine ligand changes the emission energies by altering the energy level of HOMO and LUMO but does not change the transition natures.

The binuclear gold phosphorus ylide complexes [AuI2(CH2PH2CH2)2] (1), [AuII2X2(CH2PH2CH2)2] (X = Cl (2a), Br (2b), I (2c)), [AuIII2X4(CH2PH2CH2)2] (X = Cl (3a), Br (3b)), and [AuIAuIIIX2(CH2PH2CH2)2] (X = Cl (4a), Br (4b)) were explored using density functional theory and ab initio methods. The use of methods, basis sets, and substituent effects confirmed our calculations. The analyses on their electronic structures reveal that two- and four-electron oxidation from 1 to 2−4 mainly occurs at the gold centers, resulting in their different coordination geometry features and metal−metal interactions as well as spectroscopic properties. Bond-order and frequency calculations provided the evidence for the weak Au−Au bonding interaction in 1, 3, and 4 and an approximate Au−Au single bond in 2. Unrestricted MP2 calculations showed that the triplet excited-state structures of 1, 2a, and 3a are minimum points on the potential energy surface. Upon excitation, the Au−Au distances of 1 and 3a shorten while that of 2a i...