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.

Salze des S4N4O2 – Beispiele für die Abhängigkeit de Struktur von cyclischen Schwefel‐Stickstoff‐Verbindungen von der Elektronendichte

Abstract: Die Umsetzung von S4N4O2 mit Nucleophilen (Alkoholate, Alkohole, Azide und Isocyanate) in alkoholischem Medium fuhrt zu den Salzen 1a–h. Fur 1h wurde eine Rontgenstrukturanalyse durchgefuhrt. 1h kristallisiert in der Raumgruppe P21/n und enthalt eine transannulare SS Bindung mit 248.2 (2) pm. Die Struktur von 1h wird im Zusammenhang mit der Zunahme der Elektronendichte betrachtet und mit den Ergebnissen der Rontgenstrukturanalyse von CH3Si(NSN)3SiCH3 (2) verglichen. 2 kristallisiert kubisch (Raumgruppe P4132). Das bicyclische Molekul (SN 150.4 (2), SiN 173.7 (2)pm) hat praktisch D3h Symmetrie und zeigt keine SS-Bindungen im Ring. Salts of S4N4O2 – Examples for the Dependence of the Structure of Cyclic Sulfur-Nitrogen Compounds on the Electron Density The reaction of S4N4O2 with nucleophiles (alcoholates, alcohols, azides, and isocyanates) in alcoholic solution leads to the salts 1a–h. The Structure of 1h was determined by means of an X-ray analysis. 1h crystallizes in the space group P21/n and contains a transannular SS-bond with 248.2 (2) pm. The structure of 1h is considered in connection with the increase of electron density and compared with the results of the X-ray analysis of CH3Si(NSN)3SiCH3 (2). 2 is cubic (space group P4132). The bicyclic molecule (SN 150.4(2), SiN 173.7 (2) pm) has approximate D3h symmetry and shows no SS bonds across the rings.

[Fe6S9(SCH2C6H5)2]4−: A Hexanuclear Iron-Sulfur Cluster Anion Containing the Square-Pyramidal [(μ4-S)Fe4] Unit†

Abstract: The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 489. DOI:10.1002/anie.198204890

Crystal structure and spectroscopic characterization of CsV(SO4)2. evidence for an electronic Raman transition

Abstract: Green platelike hexagonal crystals of CsV(SO 4 ) 2 were obtained by stepwise cooling in the range 500-400 o C of solutions of V 2 O 5 in Cs 2 S 2 O 7 , either under SO 2 (g) atmosphere or during catalytic conversion of SO 2 , in a 10% SO 2 , 11% O 2 , and 79% N 2 gas mixture. The crystals belong to the trigonal system, space group P3, with a=b=4.868(1) A and c=8.767(2) A at 140 K and Z=1. The phase represents a novel structure type with tetrahedral SO 4 2- ions linked to octahedrally coordinated vanadium(III) in a way different from the known KV(SO 4 ) 2 and other related M I M III (SO 4 ) 2 structures. The infrared and Raman spectra of powdered CsV(SO 4 ) 2 show close analogy to those of KV(SO 4 ) 2

Neue Oxonium‐Bromochalkogenate(IV) — Darstellung, Struktur und Eigenschaften von [H3O][TeBr5] · 3C4H8O2 und [H3O]2[SeBr6]

Abstract: Tiefrote Kristalle der Zusammensetzung [H3O][TeBr5] · 3 C4H8O2 (1) wurden aus einer gesattigten Losung von TeBr4 in wasserhaltigem 1,4-Dioxan dargestellt. In der Verbindung (Raumgruppe P21/m, a = 8.922(4) A, b = 13.204(7) A, c = 9.853(5) A, β = 91.82(4)° bei 150 K) konnte erstmals ein quadratisch-pyramidales [TeBr5]− -Anion isoliert werden. Dessen Koordinationspolyeder wird durch eine schwache Wechselwirkung mit einem 1,4-Dioxan-Molekul zu einem verzerrten Oktaeder vervollstandigt. Die [H3O]+-Kationen sind durch 1,4-Dioxan-Molekule zu Ketten verknupft. Die Saure ist bei Raumtemperatur nur in ihrer Mutterlauge stabil. [H3O]2[SeBr6] (2) (Raumgruppe Fm3m, a = 10.421(1) A bei 170 K) ist eine hochsymmetrisch kristallisierende Bromoselen(IV)-saure, mit der es gelang, ein nur sehr schwach durch Br-Atome des Anions koordiniertes [H3O]+-Ion zu isolieren. Die anionische Einheit besteht aus freien, unverzerrt oktaedrischen [SeBr6]2−-Ionen. Die Kristallstruktur ist isotyp zu K2[PtCl6]. Die Verbindung zeigt eine fur Halogenochalkogen(IV)-sauren bemerkenswerte thermische Stabilitat. Beide Oxoniumsalze wurden durch vollstandige Rontgenstrukturanalysen charakterisiert. Uber schwingungsspektroskopische Untersuchungen an 2 wird berichtet. New Oxonium Bromochalcogenates(IV) — Synthesis, Structure, and Properties of [H3O][TeBr5] · 3 C4H8O2 and [H3O]2[SeBr6] Dark red crystals of the composition [H3O][TeBr5] · 3 C4H8O2 (1) were isolated from a saturated solution of TeBr4 in 1,4-dioxane containing a small amount of water. In this compound (space group P21/m, a = 8.922(4) A, b = 13.204(7) A, c = 9.853(5) A, β = 91.82(4)° at 150 K) a square pyramidal [TeBr5]− anion has been isolated for the first time. The coordination sphere of the anion is completed to a distorted octahedron by weak interaction with a dioxane molecule of the cationic system. The [H3O]+ cations are connected to chains by dioxane molecules. At room temperature the compound is stable only in its mother liquor. Crystalline [H3O]2[SeBr6] (2) (space group Fm3m, a = 10.421(1) A at 170 K) is a bromoselenous acid of high symmetry. The [H3O]+ ion is only weakly coordinated by Br atoms of the anion. The anions are isolated octahedral [SeBr6]2− units. The structure is isotypic to the K2[PtCl6] structure. Despite being a halogenochalcogen(IV) acid, 2 exhibits a remarkable thermal stability. Both oxonium compounds were characterized by single-crystal X-ray structure analyses. Vibrational spectra of 2 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.