A simple model based on the two-electron two-orbital textbook problem is presented and used to analyze pairwise interatomic interactions in metal-ligand bonding. In particular the two types of covalency discussed during the last decade for actinide-ligand interactions, overlap/interaction driven and energy-near-degeneracy driven covalency, as well as their influence on the bond strengths and interatomic charge build-up are discussed. Hydration complexes M(H2O)n(4+) of selected tetravalent lanthanide and actinide ions are used to probe the performance of the model for an analysis of calculations as well as for predictions.

The structures and relative stabilities of complexes of the DOTA ligand with tetravalent actinide ions An4+ (An = Th, Pa, U, Np, Pu) in the gas phase and aqueous solution have been studied by relativistic An pseudopotentials combined with gradient-corrected density functional theory BP86 as well as Møller-Plesset second-order perturbation theory MP2 and the approximate coupled cluster singles and doubles model CC2. The complexes are found to become more stable along the actinide series, and the squared antiprismatic conformation is found to be lower in energy than the twisted squared antiprismatic one. Covalent actinide-ligand bonding contributions are analyzed and found to arise mainly for the actinide-oxygen bonds, and to a lesser extent for the actinide-nitrogen bonds. The performance of 5f-in-core and 5f-in-valence An pseudopotentials is compared and deviations due to the averaging over electronic states arising from the An 5f subconfiguration are analyzed by performing configuration-averaged Hartree-Fock CAHF and subsequent complete active space configuration interaction CASSCI calculations, with and without inclusion of spin-orbit interactions.

Nonadiabatic effects have been extensively studied in photoexcited processes, but their role in thermal process so far has neither been thoroughly studied nor appreciated, despite their significance. In this work, H 2 and N 2 activation mediated by a diuranium complex was studied from a nonadiabatic perspective using multi–configurational ab initio calculations combined with density functional theory. Stepwise electron transfer during the reaction enhances degeneracy between electronic states, enabling state-to-state transitions, i.e., spin downshift. The dual functionality of transition states acting as thermodynamic gateways and channels for nonadiabatic transitions was disclosed. The π and σ cooperative activation explains the unprecedented reactivity by the diuranium cooperation. Bonding analysis reveals that U 5f/6d orbitals mixing with H 1s /N 2p orbitals afford some degree of covalency to the primarily ionic U─H/N interactions, with the 6d-orbitals contributing more pronounced than the 5f-orbitals in σ interactions, while the U─N π bonding exhibits significant U 5f contributions.

The structural, photophysical, and photochemical properties of Ln(depma)(hmpa)2(NO3)3 (Ln = La, Ce, Nd, Sm, Eu, Tb, Ho, Er, and Yb) complexes 1-Ln were investigated with a multidisciplinary approach involving synthesis, photocycloaddition-based crystal engineering, spectroscopic analytical techniques and quantum chemical ab initio calculations. Depending on the Ln3+ ion the isostructural 1-Ln complexes exhibit quite different behavior upon excitation at 350-400 nm. Some 1-Ln complexes (Ln = La, Ce, Sm, Tb, Yb) emit a broad and strong band near 533 nm arising from paired anthracene moieties, whereas others (Ln = Nd, Eu, Ho, Er) do not. 1-Eu is not emissive at all, whereas 1-Nd, 1-Ho, and 1-Er exhibit a Ln3+ based luminescence. Upon irradiation with 365 nm ultraviolet (UV) light 1-Ln (Ln = La, Ce, Sm, Tb, Yb) dimerize by means of a photochemically induced [4 + 4] cycloaddition of the anthracene moieties, whereas 1-Ln (Ln = Nd, Eu, Ho, Er) remain monomers. We propose three models, based on the matching of the energy levels between the Ln3+ ion and the paired or dimerized anthracene units in the energy-resonance crossing region, as well as on internal conversion-driven and intersystem crossing-driven energy transfer, which explain the Ln3+ ion regulated photophysics and photochemistry of the 1-Ln complexes.

A simple aqueous complexing system of UO22+ with F- is selected to systematically illustrate the application of Raman spectroscopy in exploring uranyl(vi) chemistry. Five successive complexes, UO2F+, UO2F2(aq), UO2F3-, UO2F42-, and UO2F53-, are identified, as well as the formation constants except for the 1 : 5 species UO2F53-, which was experimentally observed here for the first time. The standard relative molar Raman scattering intensity for each species is obtained by deconvolution of the spectra collected during titrations. The results of relativistic quantum chemical first-principles and ab initio calculations are presented for the complete set of [UO2(H2O)mFn]2-n complexes (n = 0-5), both for the gas phase as well as for aqueous solution modelling bulk water using the conductor-like screening model. Electronic structure calculations at the M & oslash;ller-Plesset second-order perturbation theory level provide accurate geometrical parameters and in particular reveal that k water molecules in the second coordination sphere coordinating to the F- ligands in the resulting [UO2(H2O)mFn]2-n(H2O)k complexes need to be treated explicitly in order to obtain vibrational frequencies in very good agreement with experimental data. The thermodynamics and structural information obtained in this work and the developed methodology could be instructive for the future experimental and computational research on the complexation of the uranyl ion. A combined Raman spectroscopic and quantum chemical investigation provides thermodynamic and structural information of UO2F+, UO2F2(aq), UO2F3-, UO2F42-, and UO2F53- in aqueous solution.

A novel incremental scheme is presented including an incremental expansion of the virtual space for the calculation of electron correlation energies, which is compatible with any size-extensive correlation method and scales asymptotically linear for large molecules. The performance is studied for organic molecules, water clusters, and a La(III)-water complex, where the compatibility with pseudopotentials is also examined. The computational requirements are already reduced tremendously for medium-sized water clusters and hydrocarbons with respect to the canonical CCSD as well as the ordinary incremental scheme references. Correlation energies within chemical accuracy have been observed for all studied systems. The novelty of the method is that relatively small virtual spaces are used in combination with tuples of localized occupied spaces. The corresponding orthonormal occupied and virtual orbitals are obtained from QM/QM embedding calculations and can thus be used with standard quantum chemistry codes for correlation calculations. It is presented how relevant virtual spaces are selected and the correlation energies are linked in the new virtual space expansion.

A brief overview over the foundations and modern variants of the relativistic effective core potential method, i.e., energy-consistent and shape-consistent ab initio pseudopotentials as well as ab initio model potentials, is given. The energy-consistent ab initio pseudopotential approach is discussed in more detail, focussing on the uranium atom as an example. The selection of appropriate relativistic reference data, the choice of the core and the fitting procedure are discussed. Results of atomic and molecular test calculations, e.g., for the low-lying electronic states of uranium hydride, are summarized. Whereas the 5f-in-core large-core approximation provides an efficient approximate treatment of larger actinide systems without having to struggle with complexities arising from the open 5f shell, the 5f-in-valence small-core approach allows to reach a similar accuracy as the best available relativistic all-electron calculations.

The strongly luminescent and highly oxygen-sensitive Tb(III) complex [{((ArO)-Ar-MeMe)(3)tacn}Tb-III(THF)] (denoted hereafter as [1(Tb) THF]) was studied with density functional theory (DFT) and wavefunction-based ab initio electronic structure methods combined with Tb relativistic ab initio pseudopotentials. The optimized geometries as well as the calculated UV-vis absorption spectra at the DFT level agree well with the available experimental data. The calculated vertical S-0*/D-5(4) -> S-0*/F-7(J) (ligand/Tb3+ states) emission energies for J = 0-6 at the RSPT2//CASSCF level including spin-orbit corrections are 475, 511, 549, 583, 614, 638, and 644 nm, respectively, and are lower by 15, 36, 39, 39, 39, 35, and 35 nm, respectively, than the corresponding experimental values. The luminescence quenching mechanism of [1(Tb) THF] in presence of O-2 was investigated. RSPT2//CASSCF calculations for [1(Tb) THF]center dot O-2 indicate that the S-0*/F-7(J) (J = 0-6)/O-1(2) ((1)Delta(g) or (1)Sigma(+)(g)) states (ligand/Tb3+/O-2 states) are energetically more stable than the emission states S-0*/D-5(J) (J = 0-4)/O-3(2) ((3)Sigma(-)(g)). Therefore, after initial photo excitation of the ligand and subsequent energy transfer to the Tb3+ ion, the energy will be further transferred to O-2 leading to the observed luminescence quenching of [1(Tb) THF] in air. A comparison is made to [1(Sm) THF]center dot O-2 which shows a significantly smaller luminescence quantum yield and no oxygen quenching.

Molecular and electronic structures and UV-vis spectra of selected actinide(III) motexafins ([An-Motex]2+, An = Ac, Cm, Lr) as well as of uranyl(IV) motexafin ([UO2-Motex]+) were studied by using density functional theory methods combined with relativistic energy-consistent 5f-in-core actinide pseudopotentials. Solvent effects were considered by an explicit treatment of the first water coordination sphere in combination with the COSMO solvation model for bulk hydration effects. It is concluded that the Ac(III), Cm(III), Lr(III), and uranyl(IV) cations are tightly bound to the macrocyclic skeleton, yielding stable structures. By calculating the changes of the Gibbs free energies ΔG for the reactions X-Motex− + Y → X + Y-Motex− (X = La3+, Eu3+, Gd3+, Lu3+; Y =  , Am3+, Cm3+), it is found that although in aqueous solution the Motex− ligand prefers Ln3+ (Ln = Eu, Gd, Lu) over An3+ (An = Am, Cm) it rather prefers over Ln3+ (Ln = La, Eu, Gd, Lu). The results suggest that motexafin might be useful for the separation of uranyl in nuclear waste treatments and possibly also for the treatment of uranyl poisoning in vivo. In particular motexafin might be a chelating agent for 225Ac3+ in targeted α-therapy. GRAPHICAL ABSTRACT

A relativistic density functional theory (DFT) study is reported which aims to understand the complexation chemistry of An4+ ions (An = Th, U, Np, and Pu) with a potential decorporation agent, 5-LIO(Me-3,2-HOPO). The calculations show that the periodic change of the metal binding free energy has an excellent correlation with the ionic radii and such change of ionic radii also leads to the structural modulation of actinide-ligand complexes. The calculated structural and binding parameters agree well with the available experimental data. Atomic charges derived from quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis shows the major role of ligand-to-metal charge transfer in the stability of the complexes. Energy decomposition analysis, QTAIM, and electron localization function (ELF) predict that the actinide-ligand bond is dominantly ionic, but the contribution of orbital interaction is considerable and increases from Th4+ to Pu4+ . A decomposition of orbital contributions applying the extended transition state-natural orbital chemical valence method points out the significant π-donation from the oxygen donor centers to the electron-poor actinide ion. Molecular orbital analysis suggests an increasing trend of orbital mixing in the context of 5f orbital participation across the tetravalent An series (Th-Pu). However, the corresponding overlap integral is found to be smaller than in the case of 6d orbital participation. An analysis of the results from the aforementioned electronic structure methods indicates that such orbital participation possibly arises due to the energy matching of ligand and metal orbitals and carries the signature of near-degeneracy driven covalency.

Density functional theory has been used to study the biologically important coenzyme NADPH and its oxidized form NADP+ . It was found that free NADPH prefers a compact structure in gas phase and exists in more extended geometries in aqueous solution. Ultraviolet-visible absorption spectra in aqueous solution were calculated for NADPH with an explicit treatment of 100 surrounding water molecules in combination with the COSMO solvation model for bulk hydration effects. The obtained spectra using the B3LYP hybrid density functional agree quite well with experimental data. The changes of Gibbs free energies ΔG in reactions of NADPH with O2 observed experimentally in cardiovascular and in chemical systems, that is, NADPH + 2 3 O2  → NADP+  + 2 O2-  + H+ and NADPH + 1 O2  + H+  → NADP+  + H2 O2 , respectively, were calculated. The NADPH oxidation reaction in the cardiovascular system cannot proceed without activation since the obtained ΔG is positive. The reaction of NADPH in the chemical system with singlet oxygen was found to proceed in two ways, each consisting of two steps, that is, NADPH firstly reacts with 1 O2 barrierlessly to form NADP+ and HO2- , from which H2 O2 is formed in a spontaneous reaction with H+ , or 1 O2 and H+ initially form 1 HO2+ , which further reacts with NADPH to yield NADP+ and H2 O2 . © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.

Soft donor ligands often provide higher selectivity for actinides(III) over chemically similar lanthanides(III), e.g., in the AmIII-EuIII pair. Frequently, the origin of such selectivity is associated with an increased covalency in actinide-ligand bonding. However, the relationship between the degree of covalency and ion selectivity has yet to reach general consensus. Further, it is unclear whether the enhanced covalency leads to a thermodynamic stabilization of the complex or not. Using relativistic density functional theory, we have addressed these outstanding issues by analyzing the subtle change of metal-ligand interactions from a hard donor ligand to a mixed soft-hard one. The present comparative study on the structure of and binding in Am3+ and Eu3+ complexes with 3,4,3-LI(1,2-HOPO) (L) and its mixed-donor variant (LS) shows that the introduction of sulfur as a soft donor atom into the metal coordination sphere indeed infuses an Am3+ selectivity into the otherwise nonselective ligand L but also leads to a significant reduction of the metal-binding Gibbs free energies. Natural population analysis, charge decomposition analysis, and its extended version point to the critical role of ligand-to-metal charge transfer in the overall thermodynamic stability of the complexes. A detailed energy decomposition analysis combining the extended transition state with the natural orbitals chemical valence method reveals an enhancement of the covalency upon switching to the soft-hard donor ligand because of the different nature of the metal-ligand interaction. The ligand L predominantly binds the metal via π donation, whereas the ligand LS prefers σ donation. Molecular orbital and quantum theory of atoms in molecules analyses as well as a comparison to a simple model system show that the covalency occurs as a result of orbital mixing and is near-degeneracy-driven in nature. This enhanced covalency, however, fails to thermodynamically compensate for the loss of strong electrostatic interaction and thus does not lead to an additional stabilization of the metal-LS complexes.

The uranyl dication shows photocatalytic activity towards C(sp3 )-H bonds of aliphatic compounds, but not towards those of alkylbenzenes or cyclic ketones. Theoretical insights into the corresponding mechanisms are still limited. Multi-configurational ab initio calculations including relativistic effects reveal the inherent electron-transfer mechanism for the uranyl catalyzed C-H fluorination under blue light. Along the reaction path of the triplet state it was found that the hydrogen atom abstraction triggered by the electron-rich oxygen of the uranyl moiety is the rate-limiting step. The subsequent steps, that is, N-F and O-H bond breakage in a manner of concerted asynchronicity, generation of the targeted fluorinated product, and recovery of the photocatalyst are nearly barrierless. Moreover the single electron transfer between the reactive substrates plays a fundamental role during the whole photocatalytic cycle.

The weak photoluminescence of silver nanoclusters prevents their broad application as luminescent nanomaterials. Recent experiments, however, have shown that gold doping can significantly enhance the photoluminescence intensity of Ag29 nanoclusters but the molecular and physical origins of this effect remain unknown. Therefore, we have computationally explored the geometric and electronic structures of Ag29 and gold-doped Ag29-x Aux (x=1-5) nanoclusters in the S0 and S1 states. We found that 1) relativistic effects that are mainly due to the Au atoms play an important role in enhancing the fluorescence intensity, especially for highly doped Ag26 Au3 , Ag25 Au4 , and Ag24 Au5 , and that 2) heteronuclear Au-Ag bonds can increase the stability and regulate the fluorescence intensity of isomers of these gold-doped nanoclusters. These novel findings could help design doped silver nanoclusters with excellent luminescence properties.

A new approach to implement the restricted closed shell Hartree-Fock equation is proposed. In the ansatz presented, the explicit transformation of integrals from the primitive to the atomic-orbital basis is omitted. Instead, the density matrix is transformed to the primitive basis, in which it is contracted with the untransformed integrals. Obtained is the two-electron part of the Fock matrix, which is transformed back to the atomic orbital basis. The remaining steps of the self-consistent field algorithm are then performed as usual. The program presented here incorporates the most important standard techniques, such as integral prescreening, convergence acceleration (via the direct inversion of the iterative subspace ansatz), and the differential density scheme. Test calculations on standard Hartree-Fock problems were compared to the commercially available MOLPRO and TURBOMOLE program packages. Except in a few special cases, the performance of the program presented here is superior, in comparison to those two programs. Accelerations by up to a factor of 5 were found, with respect to MOLPRO calculations, and up to 3 for TURBOMOLE (in the latter case, up to 55 for generalized contracted basis sets). The program structure is independent of the type of radial contraction; however, the best results are obtained for generalized radial contraction basis sets of low contraction. The program is written in C++ and utilizes code generation engines to automatically generate the routines for the integration and density contraction. Streaming SIMD extensions are used explicitly.

AbstractDas Uranyl‐Dikation zeigt photokatalytische Aktivität gegenüber C(sp3)‐H‐Bindungen von aliphatischen Verbindungen, nicht aber von Alkylbenzolen oder cyclischen Ketonen. Nach wie vor sind die entsprechenden Mechanismen aus theoretischer Sicht unklar. Multikonfigurationale Ab‐initio‐Rechnungen mit Berücksichtigung relativistischer Effekte können den zugrundeliegenden Elektronentransfermechanismus für die Uranyl‐katalysierte C‐H‐Fluorierung in blauem Licht aufklären. Es wurde festgestellt, dass entlang dem Reaktionspfad des Triplett‐Zustands die vom elektronenreichen Sauerstoff des Uranyls ausgelöste Wasserstoffabstraktion der geschwindigkeitsbestimmende Schritt ist. Die Folgeschritte, d. h. die Brüche der N‐F‐ und der O‐H‐Bindungen in konzertierter Asynchronie, die Bildung des fluorierten Zielprodukts und die Wiederherstellung des Photokatalysators, sind nahezu barrierelos. Darüber hinaus spielt die Übertragung einzelner Elektronen zwischen den reaktiven Substraten während des ganzen Photokatalysezyklus eine wichtige Rolle.

AbstractDie schwache Photolumineszenz von Silber‐Nanoclustern verhindert ihre breite Anwendung als lumineszenter Nanowerkstoff. In jüngerer Zeit haben Experimente jedoch gezeigt, dass eine Au‐Dotierung die Intensität der Photolumineszenz von Ag29‐Nanoclustern signifikant verstärken kann, wobei die molekularen und physikalischen Ursachen dieses Effekts noch unverstanden sind. Daher haben wir rechnerisch die Geometrien und die Elektronenstrukturen von Ag29 und seinen Au‐dotierten Ag29−xAux (mit x=1–5) Nanoclustern im S0‐ und S1‐Zustand untersucht. Dabei ergab sich, dass (1) relativistische Effekte, die hauptsächlich von den Au‐Atomen herrühren, bei der Verstärkung der Fluoreszenzintensität eine wichtige Rolle spielen, insbesondere für stark dotiertes Ag26Au3, Ag25Au4 und Ag24Au5; (2) heteronukleare Au‐Ag‐Bindungen die Stabilität bei Isomeren dieser Au‐dotierten Nanocluster erhöhen und ihre Fluoreszenzintensität regulieren können. Diese neuen Ergebnisse könnten dabei helfen, dotierte Silber‐Nanocluster mit hervorragenden Lumineszenzeigenschaften zu entwickeln.

Density functional calculations have been performed to study selected hydrated lanthanide(III) motexafins (Ln-Motex(2+), Ln = La, Gd, Lu) by using energy-consistent 4f-in-core lanthanide pseudopotentials to include the major relativistic effects due to the heavy metals. The maximum number (n) of water molecules bound strongly to [Ln-Motex](2+) (Ln = La, Gd, Lu) was determined to be 6 by calculating the change of the Gibbs energies for the reactions [Ln-Motex(H2O)(n)](2+) + H2O -> [Ln-Motex(H2O)(n+1)](2+). The number of water molecules coordinated directly to Ln(3+) was found to be 3 for La, and 2 for Gd and Lu. The explicit treatment of the tightly bound water molecules in [Ln-Motex(H2O)(6)](2+) in combination with the COSMO solvation model yielded calculated reduction potentials and UV-vis absorption spectra in good agreement with available experimental data.

This Tutorial Review provides an overview of the historic and current development of the organometallic chemistry of cerium in its oxidation state 4+. Among the tetravalent lanthanide ions, only Ce4+ forms stable coordination compounds (e.g. (NH4)2[Ce(NO3)6]). Important fields of applications for cerium(iv) compounds include organic synthesis, bioinorganic chemistry, materials science, and industrial catalysis. In sharp contrast, organometallic cerium(iv) compounds are still exceedingly rare. The history of organocerium(iv) compounds is an exciting story of ups and downs. The so-called cerocene (= bis(η8-cyclooctatetraenyl) cerium) has been known since 1976. Other early reports e.g. about Cp4Ce (Cp = η5-cyclopentadienyl), were later disproven. However, significant progress in this field has been made in recent years through the use of carefully designed ligands and more sophisticated synthesis protocols. Taking the case of organocerium(iv) chemistry, this Tutorial Review also tries to exemplarily show how difficult synthetic and theoretical problems can eventually be solved through newly designed synthesis strategies (e.g. as accomplished for cyclopentadienyl and carbene derivatives) and a rewarding collaboration between synthetic and theoretical chemists (cf. the cerocene problem).