Ab Initio Analysis of Metal–Ligand Bonding in An(COT)2 with An=Th,U in Their Ground- and Core-Excited States

Relativistic multireference ab initio wave function calculations with the restricted active space second-order perturbation theory (RASPT2) were performed on thorocene and uranocene to determine the actinide N_4,5-edge and carbon K-edge X-ray absorption near-edge structure (XANES) intensities and the metal–ligand orbital mixing in the ground state and core-excited states. Calculated spectral intensities show very good agreement with the experiments and therefore allow detailed and unambiguous assignment of the observed spectral features. φ-type covalent bonding or antibonding interactions are observed for thorocene in the core-excited states, though not in the ground state. This is because the molecular orbital of φ symmetry, which is the in-phase combination of the ligand L_φ and the Th 5f_φ orbitals, can be populated with electrons in core-excited states, whereas it is essentially unoccupied in the ground state. For uranocene, the XANES spectra do not reveal much information beyond multiplet broadening, despite the presence of distinct peaks in the spectra. Every core-excited peak is best characterized by its own set of bond orbitals, as the excited state covalency is clearly different from the ground state covalency.     

Octacarbonyl Anion Complexes of the Late Lanthanides Ln(CO)8− (Ln=Tm,Yb, Lu) and the 32-Electron Rule

The lanthanide octacarbonyl anion complexes Ln(CO)₈⁻ (Ln=Tm, Yb, Lu) were produced in the gas phase and detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching-frequency region. By comparison of the experimental CO-stretching frequencies with calculated data, which are strongly red-shifted with respect to free CO, the Yb(CO)₈⁻ and Lu(CO)₈⁻ complexes were determined to possess octahedral (O_h) symmetry and a doublet X²A_2u (Yb) and singlet X¹A_1g (Lu) electronic ground state, whereas Tm(CO)₈⁻ exhibits a D_4h equilibrium geometry and a triplet X³B_1g ground state. The analysis of the electronic structures revealed that the metal-CO attractive forces come mainly from covalent orbital interactions, which are dominated by [Ln(d)]→(CO)₈ π backdonation and [Ln(d)]←(CO)₈ σ donation (contributes ≈77 and 16 % to covalent bonding, respectively). The metal f orbitals play a very minor role in the bonding. The electronic structure of all three lanthanide complexes obeys the 32-electron rule if only those electrons that occupy the valence orbitals of the metal are considered.     

Origin of the Aggregation-Induced Phosphorescence of Platinum(II) Complexes: The Role of Metal–Metal Interactions on Emission Decay in the Crystalline State

Discerning the origins of the phosphorescent aggregation-induced emission (AIE) from Pt(II) complexes is crucial for developing the broader range of photo-functional materials. Over the past few decades, several mechanisms of phosphorescent AIE have been proposed, however, not have been directly elucidated. Herein, we describe phosphorescence and deactivation processes of four class of AIE active Pt(II) complexes in the crystalline state based on experimental and theoretical investigation. These complexes show metal-to-ligand and/or metal−metal-to-ligand charge transfer emission in crystalline state with different heat resistance against thermal emission quenching. The calculated energy profiles including the minimum energy crossing point between S₀ and T₁ states were consistent with the heat resistant properties, which provided the mechanism for AIE expression. Furthermore, we have clarified the role of metal-metal interaction in AIE by comparing two computational models.     

Isolation of the Metalated Ylides [Ph3P−C−CN]M (M=Li,Na, K): Influence of the Metal Ion on the Structure and Bonding Situation

The isolation and structural characterization of the cyanido-substituted metalated ylides [Ph₃P−C−CN]M ( 1-M ; M=Li, Na, K) are reported with lithium, sodium, and potassium as metal cations. In the solid-state, most different aggregates could be determined depending on the metal and additional Lewis bases. The crown-ether complexes of sodium ( 1-Na ) and potassium ( 1-K ) exhibited different structures, with sodium preferring coordination to the nitrogen end, whereas potassium binds in an unusual η²-coordination mode to the two central carbon atoms. The formation of the yldiide was accompanied by structural changes leading to shorter C−C and longer C−N bonds. This could be attributed to the delocalization of the free electron pairs at the carbon atom into the antibonding orbitals of the CN moiety, which was confirmed by IR spectroscopy and computational studies. Detailed density functional theory calculations show that the changes in the structure and the bonding situation were most pronounced in the lithium compounds due to the higher covalency.     

Carbonate complexes [C(NH2)3]6[An(CO3)5] · nH2O (An = Th, U, Np, and Pu; n = 3 and 4): Synthesis and structures

Two series of isostructural double An(IV) and guanidinium carbonates were obtained as single crystals of the formula [C(NH₂)₃]₆[An(CO₃)₅] · nH₂O (An = Th, U, Np, and Pu; n = 3 (I) and 4 (II)) and examined by X-ray diffraction. For the Pu(IV) complexes, a = 10.490(2) Å, b = 33.798(5) Å, c = 10.519(2) Å, β = 119.414(7)°, space group P2₁/c, Z = 4, R = 0.0369 (I) and a = 16.0895(18) Å, b = 13.1458(14) Å, c = 16.6951(18) Å, β = 108.116(6)°, space group C2/c, Z = 4, R = 0.0171 (II). Both series of complexes contain the anions [An(CO₃)₅]^6?, in which the An atom is coordinated to five chelating bidenate carbonate ions. The coordination polyhedra of the An atoms are distorted bicapped square antiprisms. Within both the series, the An-O bond lengths decrease monotonically only for the sequence Th-U-Np. The average Np-O and Pu-O bond lengths in both tri- and tetrahydrates are virtually equal. The IR and electronic absorption spectra of the complexes obtained were studied. The absorption bands due to the f-f transitions experience bathochromic shifts in the spectra of the U⁴⁺ and Pu⁴⁺ carbonate complexes and hypsochromic shifts in the spectra of the Np⁴⁺ complexes.     

Stability and Structure of Binary and Ternary Metal Ion Complexes of Orotidinate 5′-Monophosphate (OMP3-) in Aqueous Solution

Abstract

The stability constants of the 1:1 complexes formed between Mg^{2 +}, Ca^{2 +}, Sr^{2 +}, Ba^{2 +}, Mn^{2 +}, Co^{2 +}, Ni^{2 +}, Cu^{2 +}, Zn ²⁺ or Cd ²⁺ and orotidinate 5′-monophosphate (OMP^3-) were determined by potentio-metric pH titrations in aqueous solution (I =0.1 M, NaNO₃; 25°C). In addition to the stability constants of these M(OMP)^? complexes, for several cases also the corresponding acidity constants for the release of the proton from the H(N-3) site were calculated; i.e., the formation of M(OMP-H)^2- complexes was quantified. On the basis of recent measurements for simple phosphate monoesters [R-MP^2-; R is a noncoordinating residue; S.S. Massoud and H. Sigel, Inorg. Chem., 27, 1447-1453 (1988)], evidence is provided that the somewhat increased stability of all the mentioned M(OMP)^? complexes is mainly the result of a charge effect of the carboxylate group (in position 6 of OMP^3-) and not of a direct participation in complex formation; i.e., there are no indications for the formation of significant amounts of macrochelates involving the phosphate and the carboxylate groups. This is different for the M(OMP-H)^2- complexes of Co ²⁺ , Ni²⁺ and Cd²⁺: in these cases significant amounts of macrochelates form; i.e., the metal ion is not only coordinated to the phosphate group but also (in part) to the ionized ^?(N-3) site, which is placed in the neighbourhood of the phosphate residue in the dominating syn conformation of this nucleotide. For the metal ions Mg^{2 +}, Ca²⁺, Sr^{2 +}, Ba²⁺ and Mn^{2 +}, which have in general a rather low affinity for N binding sites, no evidence for the formation of macrochelates is detected. In addition, the stability constants of the ternary Cu(Arm)(OMP)^? complexes, where Arm = 2,2′-bipyridyl or 1,10-phenanthroline, were determined by potentiometric pH titrations. Evaluation of the stability data shows that an equilibrium betweeen an ‘open’ isomer and a Cu(Arm)(OMP)^? species with an intramolecular stack exists; the formation degree of these aromatic ring stacks reaches about 40 percent. Overall it is quite evident that OMP^3- is a versatile ligand with remarkable properties which may be utilized by nature in recognition reactions during the intricate metabolic processes in which this nucleotide is involved.     

Crystallographic and Theoretical Investigations of Er2@C2 n (2 n=82, 84, 86): Indication of Distance-Dependent Metal–Metal Bonding Nature

Successful isolation and characterization of a series of Er-based dimetallofullerenes present valuable insights into the realm of metal–metal bonding. These species are crystallographically identified as Er₂@C_s(6)-C₈₂, Er₂@C_3v(8)-C₈₂, Er₂@C₁(12)-C₈₄, and Er₂@C_2v(9)-C₈₆, in which the structure of the C₁(12)-C₈₄ cage is unambiguously characterized for the first time by single-crystal X-ray diffraction. Interestingly, natural bond orbital analysis demonstrates that the two Er atoms in Er₂@C_s(6)-C₈₂, Er₂@C_3v(8)-C₈₂, and Er₂@C_2v(9)-C₈₆ form a two-electron-two-center Er−Er bond. However, for Er₂@C₁(12)-C₈₄, with the longest Er⋅⋅⋅Er distance, a one-electron-two-center Er−Er bond may exist. Thus, the difference in the Er⋅⋅⋅Er separation indicates distinct metal bonding natures, suggesting a distance-dependent bonding behavior for the internal dimetallic cluster. Additionally, electrochemical studies suggest that Er₂@C_82–86 are good electron donors instead of electron acceptors. Hence, this finding initiates a connection between metal–metal bonding chemistry and fullerene chemistry.     

Proton/Metal–Ligand Stability Constants of Complexes of Sr(II), Cr(II), and Al(III) with N-Phthaloyl Aminoacid and Benzimidazole Derivatives in Dioxane–Water Mixture

Russian Journal of Physical Chemistry A - Formation of complexes Sr(II), Cr(II), and Al(III) with ligands (1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)acetic acid (L1),...     

Use of Crown Ether Functions as Secondary Coordination Spheres for the Manipulation of Ligand–Metal Intramolecular Electron Transfer in Copper–Guanidine Complexes

Intramolecular electron transfer (IET) between a redox-active organic ligand and a metal in a complex is of fundamental interest and used in a variety of applications. In this work it is demonstrated that secondary coordination sphere motifs can be applied to trigger a radical change in the electronic structure of copper complexes with a redox-active guanidine ligand through ligand–metal IET. Hence, crown ether functions attached to the ligand allow the manipulation of the degree of IET between the guanidine ligand and the copper atom through metal encapsulation.     

Does Chiral Sensitivity of a Structure Depend on the Metal Core? Alkali Ion Complexes of Cyclo(Tyr-Tyr)

Alkali metal complexes of cyclic dipeptide cyclo Tyr-Tyr have been studied under cryogenic ion trap conditions. Their structure was obtained by combining Infra-Red Photo-Dissociation (IRPD) and quantum chemical calculations. The structural motif strongly depends on the relative chirality of the tyrosine residues. For residues of identical chirality, the cation interacts with one amide oxygen and one of the aromatic rings only; the distance between the aromatic rings does not change with the nature of the metal. In contrast, for residues of opposite chirality, the metal cation is located in between the two aromatic rings and interacts with both of them. The distance between the two aromatic rings strongly depends on the metal. Electronic spectra obtained by Ultra Violet Photodissociation (UVPD) spectroscopy and analysis of the UV photo-fragments shed light on the excited state deactivation processes, which depend on both the chirality of the residue and that of the metal ion core. Na⁺ stands out by the presence of low-lying charge transfer states resulting in the broadening of the electronic spectrum.     

Aggregation and Tunable Color Emission Behaviors of l-Glutamine-Derived Platinum(II) Bipyridine Complexes by Hydrogen-Bonding, π–π Stacking and Metal–Metal Interactions

A n l -glutamine-derived functional group was introduced to the bis(arylalkynyl)platinum(II) bipyridine complexes 1 – 4 . The emission could be switched between the ³MLCT excited state and the triplet excimeric state through solvent or temperature changes, which is attributed to the formation and disruption of hydrogen-bonding, π–π stacking, and metal–metal interactions. Different architectures with various morphologies, such as honeycomb nanostructures and nanospheres, were formed upon solvent variations, and these changes were accompanied by ¹H NMR and distinct emission changes. Additionally, yellow and red emissive metallogels were formed at room temperature due to the different aggregation behaviors introduced by the substituent groups on bipyridine. The thermoresponsive metallogel showed emission behavior with tunable colors by controlling the temperature. The negative Gibbs free-energy change (ΔG) and the large association constant for excimer formation have suggested that the molecules undergo aggregation through hydrogen-bonding, π–π, and metal–metal interactions, resulting in triplet excimeric emission.     

Preparation and Characterization of Uranium–Iron Triple-Bonded UFe(CO)3− and OUFe(CO)3− Complexes

We report the preparation of UFe(CO)₃⁻ and OUFe(CO)₃⁻ complexes using a laser-vaporization supersonic ion source in the gas phase. These compounds were mass-selected and characterized by infrared photodissociation spectroscopy and state-of-the-art quantum chemical studies. There are unprecedented triple bonds between U 6d/5f and Fe 3d orbitals, featuring one covalent σ bond and two Fe-to-U dative π bonds in both complexes. The uranium and iron elements are found to exist in unique formal U(I or III) and Fe(−II) oxidation states, respectively. These findings suggest that there may exist a whole family of stable df–d multiple-bonded f-element-transition-metal compounds that have not been fully recognized to date.     

Aromaticity, optical properties and zero field splitting of homo- and hetero-bimetallic (C8H8)M(μ2-,η8═C8H8)M(C8H8) where M = Ti, Zr, Th Complexes

This work presents a relativistic calculation of electron delocalization, optical properties, and zero field splitting in a group of molecules with the structure (C(8)H(8))M(μ(2)-,η(8)═C(8)H(8))M(C(8)H(8)), where M = Ti, Zr and Th. Additionally we also studied the heterobimetallic combinations (Ti-Th and Zr-Th). The molecular properties are discussed based on their electronic structure and the influence of the electron mobility in metal-metal communication. Nucleus independent chemical shift (NICS) was determined via the gauge-including-atomic-orbital (GIAO) method with the OPBE functional. The time-dependent density functional theory (TDDFT) was employed to calculate excitation energies, and the electronic transitions over 500 nm are presented with the objective to analyze the transition metal role as an antenna effect in the absorption band in the near-IR region. Finally the ZFS was calculated using Pederson-Khana and coupled perturbed DFT approaches implemented in the ORCA code. The contributions to spin-spin coupling (SS) and spin-orbit coupling (SOC) were analyzed, and the spin-density over the metal centers is discussed employing our scheme of metal-metal communication. Our aim is to determine the influence of the electronic structure over the optical and magnetic properties in a group of model compounds to understand the transition metals effect over these properties.     

New Silver(I) Complexes of Pyridyl Dithioether Ligands with Ag–Ag Interactions: Effects of Anions and Ligand Spacers on the Framework Formations of Complexes

Three new silver(I) complexes existing Ag–Ag interactions, a trinuclear cluster complex [Ag₃(L ¹)₂(NO₃)₂](NO₃) 1, a dinuclear complex [Ag₂(L ¹)₂](PF₆)₂ 2 and a one-dimensional chain complex [Ag₂ L ²(NO₃)₂] 3, where L ¹ and L ² are two structurally related pyridyl dithioether ligands, bis(2-pyridylthio)methane (L ¹) and 1,3-bis(2-pyridylthio)-propane (L ²), have been synthesized and their structures were determined by single-crystal X-ray diffraction analysis. The striking structural differences of 1 and 2 suggest that counter anions have a profound effect upon the framework formations of silver complexes with pyridyl dithioether ligands, and the differences of 1 and 3 indicate that the subtle changes of the space groups have great influence on the coordination modes of the terminal pyridylsulfanyl groups and the geometries of Ag^I ion and therefore greatly influence the structures of their complexes. The weak AgO interactions in the trinuclear complex 1 and the one-dimensinoal chain complex 3 extend them into quasi two-dimensional networks, and the AgS weak interactions in the dinuclear complex 2 into one-dimensinoal chains, and such weak interactions further stabilized these complexes.     

An alternative route for the preparation of the medical isotope 99Mo from the 238U(γ, f) and 100Mo(γ, n) reactions

The radionuclide ⁹⁹Mo, which has a half-life of 65.94 h was produced from ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions using a 10 MeV electron linac at EBC, Kharghar Navi-Mumbai, India. This has been investigated since the daughter product ^99mTc is very important from a medical point of view and can be produced in a generator from the parent ⁹⁹Mo. The activity of ⁹⁹Mo was analyzed by a γ-ray spectrometric technique using a HPGe detector. From the detected γ-rays activity of 140.5 and 739.8 keV, the amount of ⁹⁹Mo produced was determined. For comparison, the amount of ⁹⁹Mo from ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions was also estimated using the experimental photon flux from ¹⁹⁷Au(γ, n)¹⁹⁶Au reaction. The amount of ⁹⁹Mo from the detected γ-lines is in agreement with the estimated value for ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions. The production of ⁹⁹Mo activity from ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions is a relevant and novel approach, which provides alternative routes to ^235,238U(n, f) and ⁹⁸Mo(n, γ) reactions, circumventing the need for a reactor. The viability and practicality of the ⁹⁹Mo production from the ²³⁸U(γ, f) and ¹⁰⁰Mo(γ, n) reactions alternative to ^235,238U(n, f) and ⁹⁸Mo(n, γ) reactions has been emphasize. An estimate has been also arrived based on the experimental data of present work to fulfill the requirement of DOE.     

Biological Applications of Macrocyclic Schiff Base Ligands and Their Metal Complexes: A Survey of the Literature (2005–2019)

This article aims to provide a survey of biological applications of Schiff base macrocycles and their metal complexes, with emphasis given to the synthesis of the compounds and to their uses as antibacterial and antifungal agents. The literature on the subject, published during the 2005–2019 period, is shortly reviewed. This is an informed report collecting information on the addressed topic in a concise systematic way, and can be expected to be useful as a fast literature catalogue for researchers working on this and related domains.     

Swimming against the Stream? A Discussion of the Bonding in d6 and d8 Fluoro Complexes and Its Consequences for Catalytic Applications

Fluoride has recently found increasing application as coligand both in complexes of late transition metals and as a reagent in asymmetric catalysis. In recent papers, this topic was reviewed, with emphasis on the role played by so‐called ‘push‐pull interactions' between the fluoro ligand and a π acid in the stabilization of fluoro complexes with a d⁶ or d⁸ electron configuration. This picture has led to the concept that fluoride is the strongest π‐donor in the halide series. Herein, the latter concept is discussed and criticized. In particular, the effect of the ionicity of the metal‐fluoride bond is proposed as an alternative explanation to most of the observations that show a ‘reversed' halide order. The ionic character of the M F bond also accounts for its intrinsic reactivity and suggests some strategies for the stabilizatioin of fluoro complexes, including the use of coordinative unsaturation. The scope and limitations of the application of d⁶ and d⁸ fluoro complexes in catalysis are also discussed. The most promising application is the use of 16‐electron fluoro complexes in the metal‐promoted formation of the C F bond.     

Ion mobility spectrometry in scientific literature and in the International Journal for Ion Mobility Spectrometry (1998–2007)

Starting in 1998 the International Society for Ion Mobility Spectrometry, organising the annual conferences on ion mobility spectrometry, began to issue the International Journal for Ion Mobility Spectrometry. Now, in the 11th year the journal will be the first year together with SPRINGER. Therefore, the article focusses on the history of IMS providing an up to date account based on a systemetic search using the Web-of-Science and SciFinder search engines.