1,721,169 research outputs found
Electron Density distribution in Organometallic materials
Full text linkThe electron density distribution is afundamental property that provides information on the way in which atoms are held together to form molecules, polymers or supramolecular aggregates. Particular attention should be dedicated to the investigation of inorganic or organometallic materials, for their application in several fields. The goal of the research in this area is to find the inherent relationship between the actual electron density distribution of a molecule or a solid and its properties, including reactivity. This review summarizes the most recent results of electron density analysis and gives some personal perspective on future developments, focusing on applications in material science. © Schweizerische Chemische Gesellschaft
A Guided Tour Through Modern Charge Density Analysis
No full textA concise summary is provided on the basic aspects of charge density (CD) analysis and an overview of the charge density research and developments over the last 10 years. A glimpse is given to the issues which are treated in more details in the remaining chapters of this book and to those few that, although of some importance, could not be covered. Advances in experimental methodologies and in the charge density model refinements, along with progresses in quantum mechanical methods and in the interpretation/understanding of chemical bonding and interactions are briefly summarized. The increasingly stronger connection between charge density research and challenging questions of relevance to chemistry and to materials and life science is overviewed
Modern charge density studies: the entanglement of experiment and theory
Full text linkThis tutorial review article is intended to provide a general guidance to a reader interested to learn about the methodologies to obtain accurate electron density mapping in molecules and crystalline solids, from theory or from experiment, and to carry out a sensible interpretation of the results, for chemical, biochemical or materials science applications. The review mainly focuses on X-ray diffraction techniques and refinement of experimental models, in particular multipolar models. Neutron diffraction, which was widely used in the past to fix accurate positions of atoms, is now used for more specific purposes. The review illustrates three principal analyses of the experimental or theoretical electron density, based on quantum chemical, semi-empirical or empirical interpretation schemes, such as the quantum theory of atoms in molecules, the semi-classical evaluation of interaction energies and the Hirshfeld analysis. In particular, it is shown that a simple topological analysis based on a partition of the electron density cannot alone reveal the whole nature of chemical bonding. More information based on the pair density is necessary. A connection between quantum mechanics and observable quantities is given in order to provide the physical grounds to explain the observations and to justify the interpretations
Crystallographic approaches for the investigation of molecular materials: structure property relationships and reverse crystal engineering
Full text linkThis article discusses the connection between crystallography and material science. It sheds light on some of the research opportunities that are currently available and it critically reviews the directions taken by the scientific community in the field of crystal engineering. The focus is on materials formed by the assembly of organic and organometallic molecular building blocks. © Schweizerische Chemische Gesellschaft
Resonant structures and electron density analysis
No full textIn perfect resonance: The electron density distribution is typically used to analyze chemical bonding, even if strong electron delocalization occurs. The electron densities and electric potentials of picoline and the picolyl anion (see picture) have been analyzed and a detailed description of picolyl lithium complexes has been derived. The next goal is to predict chemical reactivity from electron density. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA
The future of topological analysis in experimental charge-density research
No full textIn a recent paper, Dittrich (2017) critically discussed the benefits of analysing experimental electron density within the framework of the quantum theory of atoms in molecules, often called simply the topological analysis of the charge density. The point he raised is important because it challenges the scientific production of a very active community. The question whether this kind of investigation is still sensible is intriguing and it fosters a multifaceted answer. Granted that none can predict the future of any field of science, but an alternative point of view emerges after answering three questions: Why should we investigate the electron charge (and spin) density? Is the interpretative scheme proposed by the quantum theory of atoms in molecules useful? Is an experimental charge density necessary?The state of the art and the future of the topological analysis of experimental electron charge density is the topic of this perspective article, within a debate stimulated by a recent communication
The polarizability of organometallic bonds
Full text linkThe distributed atomic polarizabilities enable the investigation of the coordination of organic ligands to transition metals giving new insight of some organometallic complexes used in catalytic processes. This approach is useful to appreciate the enormous changes occurring upon complexation to a metal, which is mainly responsible for the augmented reactivity of these species. The method we have developed allows calculating the polarizability of an atom in a molecule upon a partitioning of the electron density, for example using the Quantum Theory of Atoms in Molecules. The polarizabilities result from numerical differentiation of the atomic dipole moments with respect to the electric field. From the polarizability tensors, other useful quantities derive, for example a mathematically precise definition of bond polarizability. In terms of chemical reactivity, the distributed polarizabilities are complementary to the traditional analysis of the electrostatic potential, which informs only on susceptibility toward hard, charge-controlled chemical reactions. On the contrary, atomic polarizabilities enable addressing the sites more keen on soft, orbital-controlled reactions
Electron density building block approach for metal organic frameworks
Full text linkA general introduction to the state of the art in modeling metal organic materials using transferable atomic multipoles is provided. The method is based on the building block partitioning of the electron density, which is illustrated with some examples of potential applications and with detailed discussions of the advantages and pitfalls. The interactions taking place between building blocks are summarized and are used to discuss the properties that can be calculated
Stereoselectivity of Additions to N-Methyl Acetonitrilium Fluorosulfonate
No full textAlkoxy-N-methyl-acetiminium salts were prepared by addition of CH3OH and C2H5OH to N-methyl acetonitrilium fluorosulfonate at low temperature. Analysis of the (5)J(HH) and (3)J(13)C-H coupling constants in the NMR spectra showed an anti addition with a diastereoselectivity of >9596. Deprotonation of these salts with (Z)-configuration gave the corresponding N-methyl-alkoxyacetimines with very high (E)-configuration. Upon protonation at -78 degrees C, these iminoesters gave the corresponding alkoxy-N-methyl-acetirninium salts with (E)-configuration. Computational analyses of the iminoesters and the corresponding iminium cations including the conformations give insight into the relative stability. Nitrilium salts can be used as reagents, exemplified by some esterifications between simple acids and alcohols
Charge density analysis for crystal engineering
Full text linkThis review reports on the application of charge density analysis in the field of crystal engineering, which is one of the most growing and productive areas of the entire field of crystallography.
While methods to calculate or measure electron density are not discussed in detail, the derived quantities and tools, useful for crystal engineering analyses, are presented and their applications in the recent literature are illustrated. Potential developments and future perspectives are also highlighted and critically discussed
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