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.

Synthese, Struktur und Eigenschaften der neuen Bromoselenate(II) [Se3Br8]2−, [Se4Br14]2− und [Se5Br12]2− Kristallstrukturen von [Cu(i‐PropCN)4]2[Se3Br8], [EtPh3P]2[Se4Br14] und [n‐Prop4N]2[Se5Br12]

Abstract: Durch Symproportionierung von elementarem Selen und Selentetrabromid in polaren protischen Losungsmitteln wurde eine neue Klasse tri-, tetra- und pentanuklearer Bromoselenate(II) dargestellt. In 2-Methylpropionitril als Losungsmittel wurde das strukturell neuartige Ion [Se3Br8]2− stabilisiert und als schwarzes solvatisiertes Kupfersalz isoliert. Kristalle von [Cu(i-PropCN)4]2[Se3Br8] sind monoklin (C2/c, a = 20,753(6), b = 13,344(4), c = 19,149(6) A, β = 90,09(3)° bei 140K, Z = 4) und enthalten trigonale sternformige Ionen [Se3Br8]2−, die aus drei kantenverknupften quadratisch-planaren SeBr4-Einheiten bestehen. Die mittleren endstandigen und μ3-verbruckenden SeBr-Bindungslangen betragen 2,408 A und 2,911 A. [EtPh3P]2[Se4Br14] wurde aus Losungen in Dichlormethan in Form dunkelroter Kristalle erhalten. Wie die Rontgenstrukturanalyse zeigt (Raumgruppe P21/n, a = 11,400(3), b = 11,815(3), c = 20,720(7) A, β = 92,50(3)° bei 140K, Z = 2), enthalten sie vierkernige Ionen [Se4Br14]2−, die aus zwei parallel angeordneten, uber lineare μBr-Brucken verknupften Se2Br6-Einheiten aufgebaut sind. In diesem bemerkenswerten delokalisierten Elektronensystem muβ fur das verbruckende Brom die formale Oxidationszahl + 1 angenommen werden. Die mittlere SeBrterm-Bindungslangen sind 2,411 A, die Bruckenbindungslangen 2,764 A in den planaren Se2Br6-Einheiten sowie 2,594 A in den linearen SeBrSe-Brucken. Dunkelrotes [n-Prop4N]2[Se5Br12] konnte ebenfalls aus Losungen in CH2Cl2 dargestellt werden. Es kristallisiert tetragonal (Raumgruppe P42/mnm, a = 14,798(3), c = 11,169(2) A bei 140K, Z = 2). Seine Struktur enthalt neuartige molekulare Ionen [Se5Br12]2−, die aus einer zentralen quadratisch-planaren SeBr4-Einheit bestehen, die uber zwei trans-Kanten mit jeweils zwei weiteren quadratisch-planaren SeBr4-Einheiten verknupft ist. Das Anion kann als uber ein Selenatom verknupfte Anordnung zweier sternformiger Se3Br8-Fragmente beschrieben werden. Die mittleren endstandigen und μ3-verbruckenden SeBr-Abstande sind 2,343 A und 2,956 A. Uber schwingungsspektroskopische Untersuchungen der neuen Anionen wird berichtet. Synthesis, Structure, and Properties of the Novel Bromoselenates(II) [Se3Br8]2−, [Se4Br14]2−, and [Se5Br12]2−. Crystal Structures of [Cu(i-PropCN)4]2[Se3Br8], [EtPh3P]2[Se4Br14], and [n-Prop4N]2[Se5Br12] Using the symproportionation of elemental selenium and selenium tetrabromide in polar aprotic solvents a new class of tri-, tetra-, and pentanuclear bromoselenates(II) was obtained. In 2-methylpropionitrile solution the novel ion [Se3Br8]2− was stabilized and isolated as its black solvated copper salt. The crystals of [Cu(i-PropCN)4]2[Se3Br8] are monoclinic (C 2/c, a = 20.753(6), b = 13.344(4), c = 19.149(6) A, β = 90.09(3)° at 140K, Z = 4) and contain trigonal star-shaped ions [Se3Br8]2− consisting of three edge-sharing square planar SeBr4 units. The mean terminal and μ3-bridging SeBr bond lengths are 2.408 A, respectively. [EtPh3P]2[Se4Br14] was obtained from dichloromethane solutions as dark red square-shaped crystals. The X-ray structure analysis (space group P 21/n, a = 11.400(3), b = 11.815(3), c = 20.720(A) A, β = 92.50(3)° at 140 K, Z = 2) shows the crystals to contain tetranuclear ions [Se4Br14]2− that are built of two parallel planar [Se2Br6] units connected via two linear μBr-bridges. In the interesting delocalized electronic system a formal oxidation number of +1 has to be assigned to the bridging bromine. The mean terminal SeBr bond length is 2.411 A, the bridging bond lengths are 2.764 A in the planar Se2Br6 units 2.594 A in the linear SeBrSe bridges. Dark red [n-Prop4N]2[Se5Br12] was also isolated from CH2Cl2 solutions. It crystallizes in the tetragonal space group P 42/mnm (a = 14.798(3), c = 11.69(2) A at 140 K, Z = 2) and its structure shows the novel pentanuclear ion [se5Br12]2−, consisting of a central square planar SeBr4 unit with two of its trans-edges being shared with additional pairs of square planar SeBr4, units. The anion can be described as two star-like Se3Br8 fragments with one sharing Se. The mean terminal and μ3-bridging SeBr bond lengths are 2.343 A and 2.956 A, respectively. The vibrational spectra of the novel anions are reported and discussed.

Thallium(I)-Thiolate: Darstellung, Struktur und Eigenschaften von TlSC6H5, TlS-t-C4H9 und TlSC7H7†

Abstract: Durch Umsetzung von Thallium(I)-Salzen mit Natriumthiolaten in organischen Losungsmitteln gelang die Synthese und Kristallisation von polymeren und oligomeren neutralen TlI-Thiolat-Komplexen. Das gelbe Benzolthiolatothallium(I) TlSC6H5 (Raumgruppe P213, a = 19,943(3) A bei 143 K) enthalt in der polymeren Kristallstruktur die zwei neuartigen Strukturelemente [Tl7(SC6H5)6]+ und [Tl5(SC6H5)6]−. Die Thallium-Atome sind entweder trigonal-pyramidal oder ψ-trigonal-bipyramidal koordiniert. Das gelbe tert.-Butanthiolato-thallium(I) TlS-t-C4H9 (Raumgruppe P1, a = 11,490(3), b = 11,490(3), c = 12,698(4) A, α = 108,31(3), β = 91,21(2), σ = 116,99(3)° bei 143 K) wird aus [Tl8(S-t-C4H9)8]-Molekulen aufgebaut, wobei die Thallium-Atome wieder trigonal-pyramidal und ψ-trigonal-bipyramidal koordiniert sind. Phenylmethanthiolato-thallium(I) TlSC7H7 kristallisiert in Form dunner gelber Plattchen (Raumgruppe: Pbcn, a = 31,215(9), b = 7,173(2), c = 7,184(2) A bei 293 K). Die Kristallstruktur enthalt Thallium–Thiolat-Ketten, die strickleiterartig aus trans-verknupften Tl2S2-Vierringen bestehen. Jedes Thallium-Atom ist trigonal-pyramidal von drei Schwefel-Atomen koordiniert. Uber schwingungsspektroskopische Untersuchungen wird berichtet. Thallium(I) Thiolates: Synthesis, Structure, and Properties of TlSC6H5, TlS-t-C4H9, and TlSC7H7 By reaction of thallium(I) salts with sodium thiolates in organic solvents it is possible to synthesize and crystallize polymeric and oligomeric neutral thallium(I) thiolate complexes. The polymeric crystal structure of yellow benzenethiolato thallium(I) TlSC6H5 (space group P213, a = 19.943(3) A at 143 K) is built up by the two novel structure units [Tl7(SC6H5)6]+ and [Tl5(SC6H5)6]−. Yellow tert.-butanethiolato thallium(I) TlS-t-C4H9 (space group P1, a = 11.490(3), b = 11.490(3), c = 12.698(4) A, α = 108.31(3), β = 91.21(2), σ = 116.99(3)° at 143 K) consists of [Tl8(S-t-C4H9)8] molecules, the thallium atoms being either in trigonal pyramidal or ψ-trigonal bipyramidal coordination. Yellow phenylmethanethiolato thallium(I) TlSC7H7 crystallizes as thin plates (space group: Pbcn, a = 31.215(9), b = 7.173(2), c = 7.184(2) A at 293 K). The crystal structure contains chains of fourmembered Tl2S2 rings which are linked through trans edges to form a ladder-like arrangement. Each thallium atom is coordinated trigonal-pyramidally by three sulfur atoms. The vibrational spectra of the compounds 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.