Bernt Krebs

Bio: Bernt Krebs is an academic researcher from University of Münster. The author has contributed to research in topics: Crystal structure & Ligand. The author has an hindex of 56, co-authored 729 publications receiving 16336 citations. Previous affiliations of Bernt Krebs include Leiden University & Clariant.

K8[B12(BSe3)6]: A Novel Selenoborato‐closo‐dodecaborate with Different Anion Substitution Patterns

Abstract: Systematic studies on selenoborates containing a B12 cluster entity and alkali metal cations led to the new crystalline phase K8[B12(BSe3)6] which consists of a icosahedral B12 cluster completely saturated with trigonal-planar BSe3 units and potassium counter-ions. For the first time three different anion substitution patterns are observed in one crystal structure. The new chalcogenoborate was prepared in a solid state reaction from potassium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 850 °C. K8[B12(BSe3)6] crystallizes in the monoclinic space group Cm (no. 8) with a = 16.288(2)A, b = 41.617(4)A, c = 9.788(1)A, β = 109.59(1)°, and Z = 6. K8[B12(BSe3)6]: Ein neues Selenoborato-closo-dodecaborat mit unterschiedlichen Anionen-Substitutionsmustern Gezielte Versuche zur Synthese neuer Selenoborato-closo-dodecaborate fuhrten im ternaren Phasengebiet K/B/Se zu der neuen Verbindung K8[B12(BSe3)6], in der ein vollstandig durch Chalkogen abgesattigter B12-Ikosaeder vorliegt. Erstmals werden drei verschiedene Anionen-Substitutionsmuster innerhalb einer Kristallstruktur beobachtet. Das neue Chalkogenoborat wurde in einer Hochtemperatur-Feststoffreaktion aus Kaliumselenid, amorphem Bor und Selen in graphitierten, evakuierten Quarzglasampullen hergestellt. K8[B12(BSe3)6] kristallisiert in der monoklinen Raumgruppe Cm (Nr. 8) mit a = 16, 288(2)A, b = 41, 617(4)A, c = 9, 788(1)A, β = 109, 59(1)° und Z = 6.

Molekülstruktur und intermolekulare Koordination von acylsubstituierten Chelatkomplexen Schiffscher Basen

Abstract: Die Kristall- und Molekulstruktur von vier Schiff-Base-Komplexen mit zusatzlichen Acylgruppen an den meso-Positionen der Liganden wurde mittels Rontgenstruktur-analyse untersucht Im Nickelkomplex 5 und im Kupferkomplex 4 a ist der Sauerstoff der Acetylgruppen in den Chelatsechsringen koordiniert, wahrend die Benzoylgruppen als meso-Substituenten wirken Im Gegensatz zum Nickelkomplex 5 und zu den Kupferkomplexen 4 b und 6 a, die keinerlei intermolekulare Koordination der freien Carbonylgruppen zeigen, bildet 4 a durch intermolekulare side-on-Koordination beider Benzoylgruppen 1 D-Koordinationspolymere mit stark verzerrt oktaedrischer Koordination des Kupfers Die Molekulverkettung unterscheidet sich deutlich von der im Cobaltkomplex 3 b, bei dem nur eine der meso-Carbonylgruppen koordiniert ist, so das treppenartige Ketten mit Koordinationszahl 5 des Cobalts und einem kurzeren Metall-Oaxial-Abstand entstehen Die zentrale [Cu4O4]-Einheit in 6 a hat eine cyclooctan-ahnliche Boot-Konformation mit quadratisch-pyramidal koordiniertem Kupfer anstelle der Cubanstruktur mit trigonal-bipyramidaler Koordination in der α-Form von 6 b Molecular Structure and Intermolecular Coordination of Acyl Substituted Schiff Base Complexes The crystal and molecular structures of four Schiff base complexes with additional acyl groups on the meso positions of the ligands were investigated by means of X-ray analysis In the nickel complex 5 and in the copper complex 4 a the oxygen of the acetyl groups is coordinated within the six membered chelate rings whereas the benzoyl groups act as meso substituents In contrast to the nickel complex 5 and to the copper complexes 4 b and 6 a which do not show any intermolecular coordination of the free carbonyl groups, 4 a forms 1 D-coordination polymers with strongly distorted octahedral coordination of the copper by intermolecular side-on coordination of both of the benzoyl groups The linkage of the molecules is markedly different from that in the cobalt complex 3 b where only one of the meso acyl groups is coordinated to give stair-like chains with coordination number 5 of the cobalt and a shorter axial metal-Oaxial distance The central [Cu4O4]-unit in 6 a has a cyclooctane-like boat conformation with square-pyramidal coordinated copper instead of the cubane structure with trigonal-bipyramidal coordination in the solvent free α-form of 6 b

Zur Existenz eines Silaolefins: Synthese und Kristallstrukturen von Wittig‐ und Diels‐Alder‐Produkten in Reaktionen lithiierter fluorsilylfunktioneller Diazasilacyclopentene mit Benzaldehyd und Methacrolein

Abstract: Lithiumsalze der 1,2-Diaza-3-sila-5-cyclopentene reagieren mit Fluorsilanen und Aminofluorsilanen zu den 4-(Fluorsilyl)-substituierten Verbindungen 1 – 4. In Reaktion mit tert-Butyllithium bilden 1 – 4 erneut Lithiumsalze (5 – 8), die mit Fluorsilanen unter Zweitsubstitution zu 9 und 10 reagieren. In Wittig-analoger Reaktion reagieren 5 und 7 mit Benzaldehyd zum Benzyliden-Derivat 11. Spirocyclische Diels-Alder-Addukte (12, 13) werden aus 5 und 6 mit 2-Methyl-2-propenal erhalten. Als Nebenprodukt entsteht das Propenyliden-Derivat 14. Mit uberschussigem Dien (2-Methyl-2-propenal) reagiert 12 als Dienophil zu den oligocyclischen Diels-Alder-Addukten 15 und 16. Kristallstrukturen von 11 und 15 werden mitgeteilt. On the Existence of a Silaolefin: Synthesis and Crystal Structures of Wittig and Diels-Alder Products in Reactions of Lithiated (Fluorosilyl)diazasilacyclopentenes with Benzaldehyde and Methacrolein Lithium salts of 1,2-diaza-3-sila-5-cyclopentenes react with fluorosilanes and aminofluorosilanes to give 4-(fluorosilyl)-substituted compounds 1 – 4. By reaction with tert-butyllithium 1 – 4 themselves form lithium salts 5 – 8, which react with fluorosilanes in a second substitution giving 9 and 10.5 and 7 undergo a Wittig-type reaction with benzaldehyde to form the benzylidene derivative 11. Spirocyclic Diels-Alder adducts (12, 13) are obtained from the reaction of 5 and 6 with 2-methyl-2-propenal. The propenylidene derivative 14 is formed as a by product. With excess 2-methyl-2-propenal, 12 reacts as a dienophile giving the oligocyclic Diels-Alder adducts 15 and 16. The crystal structures of 11 and 15 are reported.

The chemistry of graphene oxide

Abstract: The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

The hydrogen bond in the solid state.

Abstract: The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties

Abstract: The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.

Multicopper Oxidases and Oxygenases

Abstract: Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.