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.

Zinc Complexes from Bromo Substituted Tris[(2‐pyridyl)methyl]amine Ligands. Influence of Sterically Demanding Substituents on Coordination Geometry

Abstract: The reaction of zinc chloride with the tripodal tetradentate ligand [(6-bromo-2-pyridyl)methyl]bis[(2-pyridyl)methyl]amine (Brtpa), bis[(6-bromo-2-pyridyl)methyl][(2-pyridyl)methyl]amine (Br2tpa), or bis[(2-pyridyl)methyl][(1-methylimidazol-2-yl)methyl]amine (bpia) yields the new coordination compounds [Zn(Brtpa)Cl2] (1), [Zn(Br2tpa)Cl2] (2) and the first zinc compound derived from bpia [Zn(bpia)Cl]2[ZnCl4]·2CH3OH (3), respectively. 1 and 2 are the first zinc complexes with halogen substituted tripodal ligands of the tpa type. The bromine substitutions of the ligands have a strong effect on coordination and binding. The new compounds were isolated and characterized by single crystal X-ray crystallography as well as infrared spectroscopy and elemental analyses. Compound 1 crystallizes in the triclinic space group P1¯ (No. 2) with a = 7.503(2) , b = 8.815(2) , c = 15.924(3)A, α = 94.19(3)°, β = 92.33(3)°, γ = 112.32(3)°, V = 969.1(3)A3, Z = 2. Compound 2 crystallizes in the monoclinic space group P21 (No. 4) with a = 8.357(1), b = 10.882(1), c = 11.286(1)A, β = 99.04(1)°, V = 1013.7(2)A3, Z = 2. Compound 3 crystallizes in the orthorhombic space group P212121 (No. 19) with a = 14.367(1), b = 17.269(1), c = 17.479(1)A, V = 4336.5(2)A3, Z = 4. Zinkkomplexe von bromsubstituierten Tris[(2-Pyridyl)methyl]amin Liganden. Der Einfluss von sterisch anspruchsvollen Substituenten auf die Koordinationsgeometrie Durch Reaktion von Zinkchlorid mit den tripodalen tetradentaten Liganden [(6-Brom-2-pyridyl)methyl]bis[(2-pyridyl)methyl]amin (Brtpa), Bis[(6-Brom-2-pyridyl)methyl][(2-pyridyl)methyl]amin (Br2tpa) und Bis[(2-pyridyl)methyl][(1-methylimidazol-2-yl)methyl]amin (bpia) konnten die neuen Komplexverbindungen [Zn(Brtpa)Cl2] (1), [Zn(Br2tpa)Cl2] (2) bzw. [Zn(bpia)Cl]2[ZnCl4]·2CH3OH (3) dargestellt werden. 1 und 2 sind die ersten Zink-Komplexe mit halogensubstituierten tripodalen Liganden des tpa-Typs. Die Bromsubstitution hat einen starken Einfluss auf die Koordination und die Bindungen in den Komplexen. Die Charakterisierung der Verbindungen erfolgte uber Einkristallrontgenstrukturanalyse und durch IR-Spektroskopie sowie Elementaranalysen. Komplex 1 kristallisiert in der triklinen Raumgruppe P1¯ (Nr. 2) mit a = 7.503(2) , b = 8.815(2) , c = 15.924(3)A, α = 94.19(3)°, β = 92.33(3)°, γ = 112.32(3)°, V = 969.1(3)A3, Z = 2. Komplex 2 kristallisiert in der monoklinen Raumgruppe P21 (Nr. 4) mit a = 8.357(1), b = 10.882(1), c = 11.286(1)A, β = 99.04(1)°, V = 1013.7(2) A3, Z = 2. Verbindung 3 kristallisiert in der orthorhombischen Raumgruppe P212121 (Nr. 19) mit a = 14.367(1), b = 17.269(1), c = 17.479(1)A, V = 4336.5(2)A3, Z = 4.

Mangan enthaltende Polyoxometallate, Synthese und Verwendung

Abstract: Manganiferous catalytically active polyoxometalates of formula (1) (Q)q (MnpAaXxYyMmOdZz(H2O)b) c H2O and the process for the manufacture thereof. In formula (I), Q, A, X, Y, M, Z, q, p, a, x, y, m, z, d, b and c have the following meaning: Q represents one or more cations selected from the group H, Li, K, Na, Rb, Cs, Ca, Mg, Sr, Ba, Al, PRRRR and NRRRR with R, R, R et R representing H or C1-C20-alkyl, C5-C8-cycloalkyl or aryl; subscript q falls in a range of 1 to 60, more especially in a range of 1 to 40 and, in the case of a single-value counter-cation, also describes the charge on the anionic unit; Mn is manganese; subscript p falls in a range of 0.1 to 10, A is a heterometal and represents one or more transitional metals of the 2 to 8 subsidiary groups except for Zn, especially Ru, V, Ti, Zr, Cr, Fe, Co, Cu, Sn, Ni, Re or Os; subscript a falls in a range of 0 to 10; X represents one or more elements selected from the group Ga, B, P, Si, Ge, As, F, Cl, Br and J; subscript x falls in the range of 0 to 10; Y represents Sb, S, Se, Te or Bi; subscript y falls in the range of 0.1 to 10; M represents one or more transition metals selected from the group Mo, W, Nb, Ta and V; subscript m falls in the range of 0.5 to 60; Z represents one or more anions selected from the group OH, F, Cl, Br, I, N3, NO3, ClO4, NCS-, SCN-, PF6, RSO3, RSO4, CF3SO3, BR4, BF4, OAc with R = H, C1-C20-alkyl, C5-C8-cycloalkyl or aryl; subscript z falls in the range 0 to 10; subscript d represents the number of oxygen atoms necessary to balance the charge and b and c are numbers in the range 0 to 50. The oxidisation catalysts described are particularly good for activating peroxide compounds and oxygen.

Cycloarsanes (AsCF3)n (n = 4, 5) – Precursors for the Highly Reactive Diarsene F3CAs=AsCF3

Abstract: Tetrakis(trifluoromethyl) cyclotetraarsane (F3CAs)4 (2) was used to repeat the UV initiated [4+2]-cycloaddition reaction of the diarsene F3CAs=AsCF3 (1) with cyclohexa-1,3-diene (CHD) and to isolate single crystals of the cycloadduct 4 for a X-ray diffraction analysis. 4 crystallizes in the space group and contains the diarsene group in its E-configuration. 2 was also applied for [2+2]-cycloaddition reactions of 1 with tBuC≡P and MeC≡CNiPr2, but in contrast to positive results with (F3CP)4 the products were too labile for isolation. However, 2 was successfully used at room temperature as precursor for coordinating 1 as π-donor ligand to the Pd(PPh3)2 complex fragment yielding η2-bis(trifluoromethyl)diarsene-bis(triphenylphosphane)-palladium(0) 5, which was characterized by X-ray diffraction of single crystals and by spectroscopic investigations (NMR, IR, MS). Attempts to prove the existence of the diarsene 1, generated by different methods, by spectroscopic studies very probably failed due to its extreme reactivity, not allowing the necessary concentrations for detection. Quantum chemical calculations of the stability of 1 with respect to dimerization, the stability of the [2+2]-cycloadduct with 1-di(isopropyl)aminopropyne and the energy difference between 4 and the 2,3-dimethyl-1,3-butadiene cycloadduct of 1 were performed to understand the considerable differences between 1 and the related diphosphene F3CP=PCF3.

Die Kristallstruktur von Kalium‐trithiowolframat‐chlorid K3(WOS3)Cl

Abstract: Eine aus chloridhaltigen Losungen von K2WOS3 kurzlich neu dargestellte Phase wurde durch eine vollstandige Rontgenstrukturanalyse als Doppelsalz aus aquimolaren Anteilen K2WOS3 und KCl charakterisiert. Raumgruppe: Pca21 mit a = 12,507 A, b = 6,3171 A, c = 12,371 A, V = 977,4 A3, Z = 4. Die als Trikaliumtrithiowolframat(VI)-chlorid K3(WOS3)Cl zu formulierende Verbindung stellt einen bisher unbekannten Strukturtyp MI2XY4 · MIZ dar. Neben isolierten tetraedrischen WOS32--Ionen (Bindungslangen W-O: 1,760 A, W–S: 2,208; 2.197; 2,196 A) liegen von K+ verzerrt oktaedrisch koordinierte Cl-Ionen und von 5S + 10 + 2Cl umgebene K+-Ionen vor. Die Bindundgsparameter des WOS32−-Ions zeigen, das in Ubereinstimmung mit anderen Chalkogeno-anionen der Ubergangsmetalle hohe π-Bindungsanteile vorliegen. Das die W–S-Bindungen aber nicht vollstandig am Bindungsausgleich beteiligt sind. A recently prepared new thiotungstate has been characterized by three-dimensional X-ray structure analysis, to be a double salt, containing K2WOS3 and KCl in equimolar proportions: potassium trithiotungstate chloride, K3(WOS3)Cl. Space group: Pca21 with a = 12.507, b = 6.317, c = 12,371 A, Z = 4. The compound represents a new structure type with stoichiometry MI2XY4 · MIZ. Besides isolated tetrahedral WOS32- ions (bond lengths W–O 1.760 A, W–S 2.208, 2.197, 2.196 A) the structure contains Cl− ions octahedrally co-ordinated by K+, the K+ ions having 5S + 10 + 2Cl as neighbours. The dimensions of the WOS32− ions in this compound show that, as in other transition metal oxo-, thio- and selenoanions, strong π bonding is present, the W–S bonds taking part in the π bond system.

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.