Charge Density Analysis of 2,6-Dinitrophenol

The charge density of 2,6-dinitrophenol has been carefully determined from low temperature (20 K) single crystal X-ray diffraction data and periodic <i>ab initio</i> theoretical calculations. The topological analysis performed on the refined densities within the framework of the Quantum Theory of Atoms in Molecules (QTAIM), allowed us to characterize, both qualitatively and quantitatively, the various intra- and intermolecular interactions existing in the crystal structure of this compound. Notably two strong intramolecular noncovalent interactions have been characterized (O···H, <i>D</i>_e > 60 kJ/mol; O···O, <i>D</i>_e ∼ 19 kJ/mol). In addition, a series of weaker intermolecular interactions (O···N, O···O, O···C, and C···C) with estimated dissociation energies of 1–9 kJ/mol have been identified

Charge Density Analysis of 2,6-Dinitrophenol

The charge density of 2,6-dinitrophenol has been carefully determined from low temperature (20 K) single crystal X-ray diffraction data and periodic <i>ab initio</i> theoretical calculations. The topological analysis performed on the refined densities within the framework of the Quantum Theory of Atoms in Molecules (QTAIM), allowed us to characterize, both qualitatively and quantitatively, the various intra- and intermolecular interactions existing in the crystal structure of this compound. Notably two strong intramolecular noncovalent interactions have been characterized (O···H, <i>D</i>_e > 60 kJ/mol; O···O, <i>D</i>_e ∼ 19 kJ/mol). In addition, a series of weaker intermolecular interactions (O···N, O···O, O···C, and C···C) with estimated dissociation energies of 1–9 kJ/mol have been identified

Nanodispersed Fe Oxide Supported Catalysts with Tuned Properties

Catalysts comprising amorphous Fe2O3 nanoparticles dispersed on silica and silica−zirconia are presented. A molecular Fe precursor was grafted on the oxide support surface by an equilibrium−adsorption method. Afterward, calcination of the material produced amorphous Fe2O3 nanoparticles on the oxide support surface. The different nature of the oxide support (SixZr1-xO2, 0.715 x < 1) imparted tunable electronic (studied by UV−vis diffuse reflectance spectroscopy), dimensional (studied by electron paramagnetic resonance spectroscopy, EPR), and redox (studied by thermal programmed reduction, TPR) properties to the samples, with following down toward their catalytic properties. The different support surfaces were covered by the iron oxide phase (from 5 to 10%), constituted of nanosized particles in a narrow size interval (between 2 and 9 nm, studied by EPR line shape and transmission electron microscopy, TEM, analyses). Homogeneous surface distribution was achieved in any case (studied by scanning electron micrographs coupled with energy dispersive X-ray spectroscopy, SEM-EDS). The precise arrangement and nuclearity of the iron oxide nanoparticles on the surface depended on the support nature. Besides, from Fe2O3 nanoaggregates (3d and 2d nanoparticles), the presence of isolated Fe3+ ions in strong interaction with the oxide support was revealed, the amount increasing with the zirconia content in the support

Charge Density and Electrostatic Potential Study of 16α,17β-Estriol and the Binding of Estrogen Molecules to the Estrogen Receptors ER_α and ER_β

An accurate X-ray diffraction study at 20 K combined with DFT theoretical calculations has been performed for the estriol crystal with two conformationally different molecules in the asymmetric unit. The electron density has been modeled via a multipole expansion, using both experimental and theoretical structure factors, and a topological analysis has been performed. The experimental molecular geometry, hydrogen bonding, atomic charges, dipole moments, and other topological characteristics are compared with those calculated theoretically. In particular, the molecular electrostatic potential has been extracted and compared with those reported for other estrogen molecules exhibiting different binding affinities to the estrogen receptors (ER_α and ER_β)

Experimental and Theoretical Electron Density Determination for Two Norbornene Derivatives: Topological Analysis Provides Insights on Reactivity

The electron density distribution of two substituted norbornene derivatives (cis-5-norbornene-endo-2,3-dicarboxylic anhydride (1) and 7-oxabicylo[2.2.1]­hept-5-ene-exo-2,3-dicarboxylic anhydride (2) has been determined from low-temperature (20 K) X-ray diffraction data and from DFT calculations with periodic boundary conditions. Topological analysis of the electron density is discussed with respect to exo-selective additions, the partial retro-Diels–Alder (rDA) character of the ground state, and intermolecular interaction energies

Charge Density and Electrostatic Potential Study of 16α,17β-Estriol and the Binding of Estrogen Molecules to the Estrogen Receptors ER_α and ER_β

An accurate X-ray diffraction study at 20 K combined with DFT theoretical calculations has been performed for the estriol crystal with two conformationally different molecules in the asymmetric unit. The electron density has been modeled via a multipole expansion, using both experimental and theoretical structure factors, and a topological analysis has been performed. The experimental molecular geometry, hydrogen bonding, atomic charges, dipole moments, and other topological characteristics are compared with those calculated theoretically. In particular, the molecular electrostatic potential has been extracted and compared with those reported for other estrogen molecules exhibiting different binding affinities to the estrogen receptors (ERα and ERβ)

Monodisperse Octahedral α-MnS and MnO Nanoparticles by the Decomposition of Manganese Oleate in the Presence of Sulfur

Octahedral monodisperse α-MnS and MnO nanoparticles have been synthesized by decomposing manganese oleate and elemental sulfur in octadecene at high (250−320 °C) temperature. The chemical composition of the obtained NPs depends on the Mn:S ratio in an unexpected way. Pure α-MnS NP samples are obtained when S:Mn ≥ 2:1, whereas pure MnO NPs require S:Mn ≤ 0.6. Variation of several parameters (concentration of sulfur, heating rate and aging temperature and time) resulted in a α-MnS NP size interval of 11−14 (from Mn monooleate) and 18−30 nm (from Mn dioleate). For MnO NPs only, size control is also possible by addition of free oleic acid (14−24 nm). Analysis of TEM tilting experiments and electron diffraction shows that both α-MnS and MnO nanoparticles have octahedral shape and spontaneously form ordered arrays with strong texture in the {111} direction. Measurement of the magnetic properties showed that α-MnS nanoparticles consist of an antiferromagnetic core and a ferromagnetic-like shell that are exchange coupled below the blocking temperature of the shell (23 K for 29 nm α-MnS NP)

Experimental and Theoretical Electron Density Determination for Two Norbornene Derivatives: Topological Analysis Provides Insights on Reactivity

The electron density distribution of two substituted norbornene derivatives (<i>cis</i>-5-norbornene-<i>endo</i>-2,3-dicarboxylic anhydride (<b>1</b>) and 7-oxabicylo[2.2.1]­hept-5-ene-<i>exo</i>-2,3-dicarboxylic anhydride (<b>2</b>) has been determined from low-temperature (20 K) X-ray diffraction data and from DFT calculations with periodic boundary conditions. Topological analysis of the electron density is discussed with respect to <i>exo</i>-selective additions, the partial <i>retro</i>-Diels–Alder (rDA) character of the ground state, and intermolecular interaction energies

Experimental and Theoretical Charge Densities of a Zinc-Containing Coordination Polymer, Zn(HCOO)₂(H₂O)₂

We present a combined experimental and theoretical charge density study of the coordination polymer Zn­(HCOO)₂(H₂O)₂, which serves as a nonmagnetic reference for the isostructural magnetic compounds containing 3d transition metals. The charge density has been modeled using the multipole formalism against a high-resolution single-crystal X-ray diffraction data set collected at 100 K. The theoretical model is based on periodic density functional theory calculations in the experimental geometry. To gauge the degree of systematic bias from the multipole model, the structure factors of the theoretical model were also projected into a multipole model and the two theoretical models are compared with the experimental results. All models, both experiment and theory, show that the Zn atom densities are highly spherical but show small accumulations of charge toward the negative ligands. The metal–ligand interactions are found to be primarily ionic, but there are subtle topological indications of covalent contributions to the bonds. The source function calculated at the bond critical points reveals a rather delocalized picture of the density in the bridging carboxylates, and this presumably reflects the exchange pathway in the magnetic analogues

Testing the Concept of Hypervalency: Charge Density Analysis of K₂SO₄

One of the most basic concepts in chemical bonding theory is the octet rule, which was introduced by Lewis in 1916, but later challenged by Pauling to explain the bonding of third-row elements. In the third row, the central atom was assumed to exceed the octet by employing d orbitals in double bonding leading to hypervalency. Ever since, polyoxoanions such as SO₄^2–, PO₄^3–, and ClO₄^– have been paradigmatic examples for the concept of hypervalency in which the double bonds resonate among the oxygen atoms. Here, we examine S–O bonding by investigating the charge density of the sulfate group, SO₄^2–, within a crystalline environment based both on experimental and theoretical methods. K₂SO₄ is a high symmetry inorganic solid, where the crystals are strongly affected by extinction effects. Therefore, high quality, very low temperature single crystal X-ray diffraction data were collected using a small crystal (∼30 μm) and a high-energy (30 keV) synchrotron beam. The experimental charge density was determined by multipole modeling, whereas a theoretical density was obtained from periodic ab initio DFT calculations. The chemical bonding was jointly analyzed within the framework of the Quantum Theory of Atoms In Molecules only using quantities derived from an experimental observable (the charge density). The combined evidence suggests a bonding situation where the S–O interactions can be characterized as highly polarized, covalent bonds, with the “single bond” description significantly prevailing over the “double bond” picture. Thus, the study rules out the hypervalent description of the sulfur atom in the sulfate group