Hans Georg von Schnering

Bio: Hans Georg von Schnering is an academic researcher from Max Planck Society. The author has contributed to research in topics: Crystal structure & Bicyclic molecule. The author has an hindex of 46, co-authored 540 publications receiving 11789 citations. Previous affiliations of Hans Georg von Schnering include University of Münster & University of Kiel.

Electron Localization in Solid-State Structures of the Elements: the Diamond Structure

Abstract: verify this result half quantitatively using a model kit as analog computer. The different sizes of C and Si are simulated with tetrahedral joints whose arm lengths differ[*] and the atoms are joined by flexible bonds (bent bonds). In disilabicyclo[l .1 .O]butane C,Si,H, (2) the region between the two C atoms does have a high ELF value (Fig. 1 c and 1 d). This confirms the previously described bond.['] The relatively small region of high ELF values implies a weak bond, in agreement with the long bond length. The white ELF maximum is also clearly off the straight topological CC connecting line. Its position is remarkably close to that of the bent bond derived from the simple structural model.IZ1 As expected, there is no bond between the Si atoms (Fig. 1 d). on the Cray-2 in Stuttgart. Mr. M. Kohout (Universitat Stuttgart) contributed to the development of the program MEROP (for the calculation of the electron density and of ELF) and wrote the program MPLOT (for drawing the contour lines of Fig. 2). The methods for obtaining localized orbitals-often used in the chemistry of molecules to describe bonding-can be used in principle for solids as well (in methane and in diamond , for example). They can lead, however, to several equivalent sets of orbitals for a given structure and are non-unique in this case. This ambiguity occurs, for example, in monomeric monocycles such as benzene, or in an infinite polyene chain.\"] In solids ambiguity often arises on account of the higher coordination, and localized orbitals are therefore used only rarely. An analysis in positional space can nevertheless be performed when instead of the equivocal localized orbitals, the electron localization function (ELF) is used. In this work we have calculated ELF for crystalline solids for the first time. The electron localization function was introduced by Becke and Edgecombe as a measure of the probability of finding an electron in the neighborhood of another electron with the same spin.\"] ELF is thus a measure of the Pauli repulsion. The explicit formulation is given in Equation (a) The parameter K is the curvature of the electron pair density for electrons of identical spin, e(r) the density at (Y), and Kh the value of K in a homogeneous electron gas with density e. The ELF values lie by definition between zero and one. Values are close to 1 when in the vicinity of one …

Refinement of the structures of GeS, GeSe, SnS and SnSe

Abstract: The orthorhombic structures (Pbnm-Di~; No. 62) of GeS, GeSe, SnS and SnSe have been refined (X-ray diffractometer data: 319 hkl, R = 0.029; 370 hkl, R = 0.061 ; 386 hkl, R = 0.062; 506 hkl, R = 0.076). The bond distances are: Ge S = 2.438(1), 2.448(2) A; Ge-Se = 2.574(2),2.564(3) A; Sn-S = 2.665(2),2.627(4) A; SnSe = 2.793(2), 2.744(3) A. The structures of these compounds reveal systematic variations of bond lengths, bond angles and of nonbonding distances. These properties as well as their temperature dependence compared to those of related compounds allow to treat these structures as different configurations of a hypothetical reaction path of a phase transition GeS type ---+ TII type ---+ NaCl type.

Homoatomic Bonding of Main Group Elements

Abstract: Clusters of main group elements are not rare. On the contrary, it is becoming difficult to avoid the discovery of new substances of this type. Clusters are the natural intermediate stages between an element and its isolated atoms or ions. In the form of polycations and polyanions they offer models for the stepwise oxidation and reduction of an element and represent a bridge between the elements. The great majority of homonuclear bonded structures are already present in the solid phases of simple systems. Mobilization of these clusters as molecules represents a great challenge.

Neue Untersuchungen über die Chloride des Molybdäns

Abstract: Die Molybdanchloride wurden einer erneuten chemischen und physikalischen Untersuchung unterworfen. Die Synthese im Temperaturgefalle lieferte die Verbindungen MoCl4, α-MoCl3 und MoCl2 (≙Mo6Cl12) in reiner, kristallisierter Form. Auf gleichem Wege wurde die neue Verbindung MoCl3,08 („β-MoCl3”) gefunden. Das im festen Zustande dimere MoCl5 verdampft monomolekular (Massenspektrometer). Der thermische Zerfall (Thermogravimetrie, Massenspektrometer) von MoCl3 erfolgt nach wahrend MoCl2 nach . Kristallstrukturuntersuchungen lieferten folgende Informationen: MoCl4 kristallisiert trigonal in einem Schichtengitter mit hexagonal dichter Cl-Packung. Die Mo-Atome besetzen 75% der Metallplatze einer Trichloridstruktur, wobei im Mikrobereich Ordnungszustande auftreten. α-MoCl3 und β-MoCl3 kristallisieren monoklin in Schichtengittern mit kubisch (α) bzw. hexagonal (β) dichter Cl-Packung. Die Mo-Atome sind paarweise als Mo2-Gruppen aneinander gebunden (MoMo = 2,76 A). Mo6Cl12(MoCl2) kristallisiert orthorhombisch. Die Struktur enthalt [Mo6Cl8]-Gruppen, die 2-dimensional unendlich miteinander verknupft sind: {[Mo6Cl8]Cl2}Cl4/2. Die Bindungsabstande MoMo innerhalb der regularen Mo6-Oktaeder betragen 2,61 A. Der Vergleich der Vergleich der Raumbeanspruchung („pro Cl”) zeigt, das diese beim Ubergang von den hoheren Molybdanchloriden zum Mo6Cl12 wegen dessen sperrigen Aufbaus sprunghaft groser wird. Magnetische Messungen liefern fur MoCl5 und MoCl4 nahezu den reinen Spinwert, wahrend die fur α-MoCl3, β-MoCl3 und Mo6Cl12 gemessenen Werte wegen der MoMo-Wechselwirkungen sehr viel kleiner sing. Mo6Br12, Mo6J12, W6Cl12, W6Br12 und W6J12 sind mit Mo6Cl12 isotyp. Chemical and physical properties of the molybdenum chlorides have been reinvestigated. By synthesis in a temperature gradient crystalline samples of MoCl4, α-MoCl3 and MoCl2 (≙Mo6Cl12) were prepared. The new compound MoCl3,08 (“β-MoCl3”) was found in the same way. MoCl5, being dimeric in the solid state, is monomeric in the vapour (mass spectrum). Thermal dissociation (TGA, mass spectrum) of MoCl3 proceeds according to 2 MoCl3 MoCl2 + MoCl4,g; P(MoCl4, 800°C) = 12 atm, whereas MoCl2 decomposes according to 2 MoCl2 Mo + MoCl4,g; P(MoCl4, 860°C) = 0,4 atm. Crystal structure analyses submitted the following informations: MoCl4 (trigonal) forms a layer structure with a hexagonal closepacked Cl sequence. Three quarters of the metal positions of a corresponding trichloride structure are randomly occupied by Mo atoms. α-MoCl3 and β-MoCl3 (both monoclinic) have layer structures with cubic (α) and hexagonal (β) close Cl arrangements and with certain adjacent octahedral holes occupied by molybdenum forming Mo2 pairs (MoMo = 2,76 A). Mo6Cl12 (MoCl2) (orthorhombic) is built up by [Mo6Cl8] clusters, linked to a 2-dimensional arrangement: {[Mo6Cl8]Cl2}Cl4/2. The MoMo distance in the regular octahedral Me6 group is 2,61 A. Comparing the volumes per one Cl atom, it can be seen, that these are abruptly increased on going from the molybdenum chlorides of higher oxidation state to Mo6Cl12 with its cumbersome structure. The magnetic moments of MoCl5 and MoCl4 nearly correspond to the spin-only values, whereas the moments of α-MoCl3, β-MoCl3, and Mo6Cl12 are much smaller, caused by MoMo interaction. Mo6Br12, Mo6I12, W6Cl12, W6Br12, and W6J12 are isotypic with Mo6Cl12.

Multiwfn: a multifunctional wavefunction analyzer.

Abstract: Multiwfn is a multifunctional program for wavefunction analysis. Its main functions are: (1) Calculating and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population analysis. (3) Bond order analysis. (4) Orbital composition analysis. (5) Plot density-of-states and spectrum. (6) Topology analysis for electron density. Some other useful utilities involved in quantum chemistry studies are also provided. The built-in graph module enables the results of wavefunction analysis to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com.

Aryl-aryl bond formation by transition-metal-catalyzed direct arylation.

Abstract: The biaryl structural motif is a predominant feature in many pharmaceutically relevant and biologically active compounds. As a result, for over a century 1 organic chemists have sought to develop new and more efficient aryl -aryl bond-forming methods. Although there exist a variety of routes for the construction of aryl -aryl bonds, arguably the most common method is through the use of transition-metalmediated reactions. 2-4 While earlier reports focused on the use of stoichiometric quantities of a transition metal to carry out the desired transformation, modern methods of transitionmetal-catalyzed aryl -aryl coupling have focused on the development of high-yielding reactions achieved with excellent selectivity and high functional group tolerance under mild reaction conditions. Typically, these reactions involve either the coupling of an aryl halide or pseudohalide with an organometallic reagent (Scheme 1), or the homocoupling of two aryl halides or two organometallic reagents. Although a number of improvements have developed the former process into an industrially very useful and attractive method for the construction of aryl -aryl bonds, the need still exists for more efficient routes whereby the same outcome is accomplished, but with reduced waste and in fewer steps. In particular, the obligation to use coupling partners that are both activated is wasteful since it necessitates the installation and then subsequent disposal of stoichiometric activating agents. Furthermore, preparation of preactivated aryl substrates often requires several steps, which in itself can be a time-consuming and economically inefficient process.

Classification of chemical bonds based on topological analysis of electron localization functions

Abstract: THE definitions currently used to classify chemical bonds (in terms of bond order, covalency versus ionicity and so forth) are derived from approximate theories1–3 and are often imprecise. Here we outline a first step towards a more rigorous means of classification based on topological analysis of local quantum-mechanical functions related to the Pauli exclusion principle. The local maxima of these functions define 'localization attractors', of which there are only three basic types: bonding, non-bonding and core. Bonding attractors lie between the core attractors (which themselves surround the atomic nuclei) and characterize the shared-electron interactions. The number of bond attractors is related to the bond multiplicity. The spatial organization of localization attractors provides a basis for a well-defined classification of bonds, allowing an absolute characterization of covalency versus ionicity to be obtained from observable properties such as electron densities.

Engineering coordination polymers towards applications

Abstract: The development in the field of coordination polymers or metal-organic coordination networks, MOCNs (metal-organic frameworks, MOFs) is assessed in terms of property investigations in the areas of catalysis, chirality, conductivity, luminescence, magnetism, spin-transition (spin-crossover), non-linear optics (NLO) and porosity or zeolitic behavior upon which potential applications could be based.