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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.


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Journal ArticleDOI
TL;DR: The three selenoborates Rb8[B12(BSe3)6] (P1, a, b, c, n, n 1.860(2) A, b = 10.450(3)
Abstract: Die Selenoborate Rb8[B12(BSe3)6] (P1, a = 10,512(5) A, b = 10,450(3) A, c = 10,946(4) A, α = 104,53(3)°, β = 91,16(3)°, γ = 109,11(3)°, Z = 1), Cs4Hg2[B12(BSe3)6] (P1, a = 9,860(2) A, b = 10,740(2) A, c = 11,078(2) A, α = 99,94(3)°, β = 90,81(3)°, γ = 115,97(3)°, Z = 1) und Rb4Hg2[B12(BSe3)6] (P1, a = 9,593(2) A, b = 10,458(2) A, c = 11,131(2) A, α = 99,25(3)°, β = 91,16(3)°, γ = 116,30(3)°, Z = 1) wurden aus den Metallseleniden, amorphem Bor und Selen in Hochtemperatur-Feststoffreaktionen bei 700 °C dargestellt. Alle drei Verbindungen enthalten als charakteristisches Strukturelement B12-closo-Cluster, die uber je zwei Selenatome trigonal-planarer BSe3-Einheiten vollstandig substituiert sind. Die beiden isotypen Verbindungen Rb4Hg2[B12(BSe3)6] und Cs4Hg2[B12(BSe3)6] sind die ersten durch Einkristall-Rontgenstrukturanalyse eindeutig charakterisierten Selenoboratstrukturen, die ein Ubergangsmetall enthalten. Three Novel Selenoborato-closo-dodecaborates: Syntheses and Crystal Structures of Rb8[B12(BSe3)6], Rb4Hg2[B12(BSe3)6], and Cs4Hg2[B12(BSe3)6] The three selenoborates Rb8[B12(BSe3)6] (P1, a = 10.512(5) A, b = 10.450(3) A, c = 10.946(4) A, α = 104.53(3)°, β = 91.16(3)°, γ = 109.11(3)°, Z = 1), Cs4Hg2[B12(BSe3)6] (P1, a = 9.860(2) A, b = 10.740(2) A, c = 11.078(2) A, α = 99.94(3)°, β = 90.81(3)°, γ = 115.97(3)°, Z = 1), and Rb4Hg2[B12(BSe3)6] (P1, a = 9.593(2) A, b = 10.458(2) A, c = 11.131(2) A, α = 99.25(3)°, β = 91.16(3)°, γ = 116.30(3)°, Z = 1) were prepared from the metal selenides, amorphous boron and selenium by solid state reactions at 700 °C. These new chalcogenoborates contain B12 icosahedra completely saturated with six trigonal-planar BSe3 entities functioning as bidentate ligands to form a persubstituted closo-dodecaborate anion. The two isotypic compounds Rb4Hg2[B12(BSe3)6] and Cs4Hg2[B12(BSe3)6] are the first selenoborate structures containing a transition metal which are characterized by single crystal diffraction.

14 citations

Journal ArticleDOI
TL;DR: In this paper, the synthesis and structural characterization of the iron-III complexes of the tripodal ligands N-Acetyl-N′, N′-bis[(2-pyridyl)methyl]ethylenediamine (uns-penp), [Fe(unspenp)Cl2]ClO4·CH3CN, [{Fe(nsppCl}2O](ClO 4)2·H2O, [Fe[nspP]Br]·(C2H5)2O (tcc
Abstract: Synthesis and structural characterization of the iron(III) complexes of the tripodal ligands N′,N′-bis[(2-pyridyl)methyl]ethylenediamine (uns-penp), [Fe(uns-penp)Cl2]ClO4·CH3CN, [{Fe(uns-penp)Cl}2O](ClO4)2·2CH3CN and the amide derivative N-Acetyl-N′,N′-bis[(2-pyridyl)methyl]ethylenediamine (acetyl-uns-penp), [Fe2(acetyl-uns-penp)2O](ClO4)2·H2O, [Fe(acetyl-uns-penp)(tcc)Br]·(C2H5)2O (tcc = tetrachlorocatecholate), and [{Fe(acetyl-uns-penp)(tcc)}2O]·(C2H5)2O·CH3OH are reported. Catechol dioxygenase reactivity of in situ prepared complex solutions was tested and showed that all complexes reacted slower compared with the iron tmpa system described in the literature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

14 citations

Journal ArticleDOI
TL;DR: Mn2O7 can be described as a defect-anti-type of CaF2 as discussed by the authors, and the bridging MnOMn angle is 120.7°.
Abstract: Mn2O7 kristallisiert monoklin mit a = 679,56 pm, b = 1668,7 pm, c = 945,4 pm, β = 100,20°, Z = 8 in der Raumgruppe P21/c. Das Mn2O7-Molekul besteht aus zwei uber ein verbruckendes O-Atom verknupften MnO4-Tetraedern; der Bruckenwinkel MnOMn betragt 120,7°. Die Bindungsabstande MnO sind 177,0 pm (Brucke) sowie 2 × 160,0 pm und 158,5 pm im MnO4-Tetraeder. Im festen Zustand sind die Mn2O7-Molekule in einer Weise gepackt, das die Anordnung der O-Atome im Kristall einer kubisch dichtesten Kugelpackung entspricht, d. h. Mn2O7 last sich einfach als Defekt-anti-CaF2-Typ beschreiben. Die geometrischen Eigenschaften von Mn2O7 werden anderen Molekulstrukturen gegenuber-gestellt; insbesondere werden Mn2O7 und Tc2O7 bezuglich Struktur und Bindung verglichen. Crystal and Molecular Structure of Manganese (VII) Oxide Mn2O7 crystallizes in the monoclinic space group P21/c with a = 679.56 pm, b = 1668.7 pm, c = 945.4 pm, β = 100.20°, Z = 8. The Mn2O7 molecule consists of cornersharing pairs of MnO4 tetrahedra; the bridging MnOMn angle is 120.7°. The MnO bond lengths are 177.0 pm (bridge), 2 × 160.0 pm and 158.5 pm in the MnO4 tetrahedron. In the crystal the Mn2O7 molecules are packed in a way to yield the arrangement of a cubic close packing for the O atoms. Formally Mn2O7 can be described as a defect-anti-type of CaF2. We compare the geometrical properties of Mn2O7 with other molecular structures with an emphasis on the difference of structure and bonding between Mn2O7 and Tc2O7.

14 citations

Journal ArticleDOI
TL;DR: In this article, the manganese substituted heteropolytungstates α-[(Mn(H2O))SiW11O39]6− (1), α[(H 2O))2SiW10O38]8− (2), α [(MmN(O))3SiW9O37]10− (3), β [MnN 2O]3PW 9O17]9− (4], and α[Mn N 2O])3PWC 9O37 ]9−(5
Abstract: The manganese substituted heteropolytungstates α-[(Mn(H2O))SiW11O39]6− (1), α-[(Mn(H2O))2SiW10O38]8− (2), α-[(Mn(H2O))3SiW9O37]10− (3), β-[(Mn(H2O))3SiW9O37]10− (4), and α-[(Mn(H2O))3PW9O37]9− (5) were applied as catalysts for low-temperature bleaching of stained cotton cloth. The bleaching activity of this series of catalysts is correlated to the fibre-damage induced to cotton cloths during washing as well as to the stability of the catalysts under simulated washing conditions.

14 citations


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TL;DR: 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.
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)

10,126 citations

Journal ArticleDOI
01 Apr 1988-Nature
TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
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

9,929 citations

Journal ArticleDOI
TL;DR: The hydrogen bond is the most important of all directional intermolecular interactions, operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological.
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.

5,153 citations

Journal ArticleDOI
TL;DR: The transition metal dichalcogenides are about 60 in number as discussed by the authors, and two-thirds of these assume layer structures and can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions.
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.

3,313 citations

Journal ArticleDOI
TL;DR: 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 or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers.
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.

3,241 citations