The Electron-Density Distribution of UCl and Its Topology from X-ray Diffraction.

The chemistry of electrons in actinide complexes and materials is still poorly understood and represents a serious challenge and opportunity for experiment and theory. The study of the electron density distribution of the ground state of such systems through X-ray diffraction represents a unique opportunity to quantitatively investigate different chemical bonding interactions at once, but was considered "almost impossible" on heavy-atom systems, until very recently. Here, we present a combined experimental and theoretical investigation of the electron density distribution in UCl_ crystals and comparison with the previously reported spin density distribution from polarized neutron diffraction.

Tailoring chemical bonds to design unconventional glasses.

Glasses are commonly described as disordered counterparts of the corresponding crystals; both usually share the same short-range order, but glasses lack long-range order. Here, a quantification of chemical bonding in a series of glasses and their corresponding crystals is performed, employing two quantum-chemical bonding descriptors, the number of electrons transferred and shared between adjacent atoms. For popular glasses like SiO, GeSe, and GeSe, the quantum-chemical bonding descriptors of the glass and the corresponding crystal hardly differ.

Metavalent or Hypervalent Bonding: Is There a Chance for Reconciliation?

A family of solids including crystalline phase change materials such as GeTe and Sb Te , topological insulators like Bi Se and halide perovskites such as CsPbI possesses an unconventional property portfolio that seems incompatible with ionic, metallic, or covalent bonding. Instead, evidence is found for a bonding mechanism characterized by half-filled p-bands and a competition between electron localization and delocalization. Different bonding concepts have recently been suggested based on quantum chemical bonding descriptors which either define the bonds in these solids as electron-deficient (metavalent) or electron-rich (hypervalent).

Carbonyl-Based Redox-Active Compounds as Organic Electrodes for Batteries: Escape from Middle-High Redox Potentials and Further Improvement?

Extracting─from the vast space of organic compounds─the best electrode candidates for achieving energy material breakthrough requires the identification of the microscopic causes and origins of various macroscopic features, including notably electrochemical and conduction properties. As a first guess of their capabilities, molecular DFT calculations and quantum theory of atoms in molecules (QTAIM)-derived indicators were applied to explore the family of pyrano[3,2-]pyran-2,6-dione (PPD, , A0) compounds, expanded to A0 fused with various kinds of rings (benzene, fluorinated benzene, thiophene, and merged thiophene/benzene). A glimpse of up-to-now elusive key incidences of introducing oxygen in vicinity to the carbonyl redox center within 6MRs─as embedded in the A0 core central unit common to all A-type compounds─has been gained.

Electronic Properties of Functionalized Diamanes for Field-Emission Displays.

Ultrathin diamond films, or diamanes, are promising quasi-2D materials that are characterized by high stiffness, extreme wear resistance, high thermal conductivity, and chemical stability. Surface functionalization of multilayer graphene with different stackings of layers could be an interesting opportunity to induce proper electronic properties into diamanes. Combination of these electronic properties together with extraordinary mechanical ones will lead to their applications as field-emission displays substituting original devices with light-emitting diodes or organic light-emitting diodes.

Seeking for Optimal Excited States in Photoinduced Electron-Transfer Processes─The Case Study of Brooker's Merocyanine.

Material design enters an era in which control of electrons in atoms, molecules, and materials is an essential property to be predicted and thoroughly understood in view of discovering new compounds with properties optimized toward specific optical/optoelectronic applications. π-electronic delocalization and charge separation/recombination enter notably into the set of features that are highly desirable to tailor. Diverse domains are particularly relying on photoinduced electron-transfer (PET), including fields of paramount importance such as energy production through light-harvesting, efficient chemoreceptive sensors, or organic field-effect transistors.

Revisiting the Nature of Chemical Bonding in Chalcogenides to Explain and Design their Properties.

Quantum chemical bonding descriptors have recently been utilized to design materials with tailored properties. Their usage to facilitate a quantitative description of bonding in chalcogenides as well as the transition between different bonding mechanisms is reviewed. More importantly, these descriptors can also be employed as property predictors for several important material characteristics, including optical and transport properties.

Atomic Group Decomposition of Charge Transfer Excitation Global Indexes.

A model for decomposing the Le Bahers, Adamo, and Ciofini Charge Transfer (CT) Excitations global indexes ( 2011, 7, 2498-2506) into molecular subdomains contributions is presented and a software, DOCTRINE (atomic group Decomposition Of the Charge TRansfer INdExes) for the implementation of this novel model has been coded. Although our method applies to any fuzzy or to any disjoint exhaustive partitioning of the real space, it is here applied using a definition of chemically relevant molecular subdomains based on the Atoms in Molecules Bader basins. This choice has the relevant advantage of associating or subdomain contributions to rigorously defined quantum objects, yet bearing a clear chemical meaning.

Unravelling functions of halogen substituents in the enantioseparation of halogenated planar chiral ferrocenes on polysaccharide-based chiral stationary phases: experimental and electrostatic potential analyses.

Planar chiral halogenated ferrocenes have come in useful as synthetic intermediates over the years, allowing for the preparation of functionalized derivatives for catalysis, material science, optoelectronics, and medicinal chemistry. Despite their chemical interest, few halogenated planar chiral ferrocenes have been prepared in enantiopure form by asymmetric synthesis so far. Enantioselective HPLC on polysaccharide-based chiral stationary phases (CSPs) has been used for resolving planar chiral ferrocenes making both enantiomers available.

Topology of the Electron Density and of Its Laplacian from Periodic LCAO Calculations on -Electron Materials: The Case of Cesium Uranyl Chloride.

The chemistry of -electrons in lanthanide and actinide materials is yet to be fully rationalized. Quantum-mechanical simulations can provide useful complementary insight to that obtained from experiments. The quantum theory of atoms in molecules and crystals (QTAIMAC), through thorough topological analysis of the electron density (often complemented by that of its Laplacian) constitutes a general and robust theoretical framework to analyze chemical bonding features from a computed wave function.

Prognostic Role of Circulating Tumor Cells in Metastatic Renal Cell Carcinoma: A Large, Multicenter, Prospective Trial.

Background: Circulating tumor cells (CTCs) correlate with adverse prognosis in patients with breast, colorectal, lung, and prostate cancer. Little data are available for renal cell carcinoma (RCC).

Materials And Methods: We designed a multicenter prospective observational study to assess the correlation between CTC counts and progression-free survival (PFS) in patients with metastatic RCC treated with an antiangiogenic tyrosine kinase inhibitor as a first-line regimen; overall survival (OS) and response were secondary objectives.

Redox Potential and Crystal Chemistry of Hexanuclear Cluster Compounds.

Most of TM-cluster compounds (TM = transition metal) are soluble in polar solvents, in which the cluster units commonly remain intact, preserving the same atomic arrangement as in solids. Consequently, the redox potential is often used to characterize structural and electronic features of respective solids. Although a high lability and variety of ligands allow for tuning of redox potential and of the related spectroscopic properties in wide ranges, the mechanism of this tuning is still unclear.

Computational Modeling of 2D Materials under High Pressure and Their Chemical Bonding: Silicene as Possible Field-Effect Transistor.

To study the possibility for silicene to be employed as a field-effect transistor (FET) pressure sensor, we explore the chemistry of monolayer and multilayered silicene focusing on the change in hybridization under pressure. computations show that the effect of pressure depends greatly on the thickness of the silicene film, but also reveals the influence of real experimental conditions, where the pressure is not hydrostatic. For this purpose, we introduce anisotropic strain states.

Charge Density Analysis of Actinide Compounds from the Quantum Theory of Atoms in Molecules and Crystals.

The nature of chemical bonding in actinide compounds (molecular complexes and materials) remains elusive in many respects. A thorough analysis of their electron charge distribution can prove decisive in elucidating bonding trends and oxidation states along the series. However, the accurate determination and robust analysis of the charge density of actinide compounds pose several challenges from both experimental and theoretical perspectives.

Metal-Metal Bond in the Light of Pauling's Rules.

About 70 years ago, in the framework of his theory of chemical bonding, Pauling proposed an empirical correlation between the bond valences (or effective bond orders (BOs)) and the bond lengths. Till now, this simple correlation, basic in the bond valence model (BVM), is widely used in crystal chemistry, but it was considered irrelevant for metal-metal bonds. An extensive analysis of the quantum chemistry data computed in the last years confirms very well the validity of Pauling's correlation for both localized and delocalized interactions.

Enantioseparation of 5,5'-Dibromo-2,2'-Dichloro-3-Selanyl-4,4'-Bipyridines on Polysaccharide-Based Chiral Stationary Phases: Exploring Chalcogen Bonds in Liquid-Phase Chromatography.

The chalcogen bond (ChB) is a noncovalent interaction based on electrophilic features of regions of electron charge density depletion (σ-holes) located on bound atoms of group VI. The σ-holes of sulfur and heavy chalcogen atoms (Se, Te) (donors) can interact through their positive electrostatic potential () with nucleophilic partners such as lone pairs, π-clouds, and anions (acceptors). In the last few years, promising applications of ChBs in catalysis, crystal engineering, molecular biology, and supramolecular chemistry have been reported.

Looking at local classical and quantum forces in stable crystals using multipole-model refined electron densities and orbital-free DFT approximations.

Two distinct approaches, that of energy and that of force, are adopted in quantum mechanics to get insights on chemical processes. In the second one, the net forces acting on the electrons and nuclei in a system (Ehrnefest and Hellmann-Feynman forces, respectively) are determined and a local version of the approach, in terms of force density fields rather than forces, has also been proposed for electrons. This is the path followed by Tsirelson & Stash (2020) in this issue of Acta Crystallographica Section B, to study for the first time the spatial distribution of the electronic forces of different nature acting in stable crystals.

Factors Impacting σ- and π-Hole Regions as Revealed by the Electrostatic Potential and Its Source Function Reconstruction: The Case of 4,4'-Bipyridine Derivatives.

Positive electrostatic potential () values are often associated with σ- and π-holes, regions of lower electron density which can interact with electron-rich sites to form noncovalent interactions. Factors impacting σ- and π-holes may thus be monitored in terms of the shape and values of the resulting . Further precious insights into such factors are obtained through a rigorous decomposition of the values in atomic or atomic group contributions, a task here achieved by extending the Bader-Gatti source function (SF) for the electron density to .

Spin Density Topology.

Despite its role in spin density functional theory and it being the basic observable for describing and understanding magnetic phenomena, few studies have appeared on the electron spin density subtleties thus far. A systematic full topological analysis of this function is lacking, seemingly in contrast to the blossoming in the last 20 years of many studies on the topological features of other scalar fields of chemical interest. We aim to fill this gap by unveiling the kind of information hidden in the spin density distribution that only its topology can disclose.

A tool for deciphering the redox potential ranking of organic compounds: a case study of biomass-extracted quinones for sustainable energy.

Carbonyl compounds have emerged as promising organic electrodes for sustainable energy storage. Accelerating the process of performant materials discovery relies on the possibility of developing methodologies to enable scanning of various sets of candidates. The genesis of this educated guess strategy must be privileged to reduce the search space of experiments, accelerate this research area and contribute to sustainable effort.

A revisit of the bond valence model makes it universal.

The use of simple, intuitive equations to correlate the geometry of crystal structures with electron descriptors of chemical bonds and material structural stability is a great advantage of the Bond Valence Model (BVM), which is based on Pauling's principles of bond order (BO) conservation and exponential BO/bond length relationship. However, the high potential of BVM to be used as an important analytical tool was overlooked in recent inorganic chemistry due to its empirical character and serious restrictions for its application. Recent quantum chemistry data (BOs and electron densities at the bond critical points, ρc) enable us to establish the validity of the BVM to any type of chemical bonds, as well as a direct BO/ρc relationship.

Expression and interactions of stereochemically active lone pairs and their relation to structural distortions and thermal conductivity.

In chemistry, stereochemically active lone pairs are typically described as an important non-bonding effect, and recent interest has centred on understanding the derived effect of lone pair expression on physical properties such as thermal conductivity. To manipulate such properties, it is essential to understand the conditions that lead to lone pair expression and provide a quantitative chemical description of their identity to allow comparison between systems. Here, density functional theory calculations are used first to establish the presence of stereochemically active lone pairs on antimony in the archetypical chalcogenide MnSbO.

Halogen bond in separation science: A critical analysis across experimental and theoretical results.

The halogen bond (XB) is a noncovalent interaction involving a halogen acting as electrophile and a Lewis base. In the last decades XB has found practical application in several fields. Nevertheless, despite the pivotal role of noncovalent interactions in separation science, investigations of XB in this field are still in their infancy, and so far a limited number of studies focusing on solid phase extraction, liquid-liquid microextraction, liquid-phase chromatography, and gas chromatography separation have been published.