Showing papers by "Bernt Krebs published in 1987"

Pentacoordinate zinc complexes of imidazole nitrogen donors as structural models for the active site in enzymes: preparation and crystal structures of (.mu.-2,2'-biimidazole)tetrakis(2,2'-biimidazole)dizinc(II) tetraperchlorate trihydrate and bis(2,2'-biimidazole)(formato)zinc(II) perchlorate

Abstract: Le premier compose du titre cristallise dans le systeme orthorhombique avec le groupe d'espace P2 1 2 1 2 1 . Le second cristallise dans le systeme monoclinique avec le groupe d'espace P2 1 /c. Affinement de la structure jusqu'a 4,34% et 4,78% respectivement

Copper(I) and copper(II) compounds of a dinucleating, octadentate tetrakisbenzimidazole ligand. Crystal and molecular structures of three dihalogeno{1,8-bis[bis(1′-methylbenzimidazol-2′-ylmethyl)amino]-3,6-dioxaoctane}dicopper(II) bis(anion) compounds (halogen = F, Cl, or Br; anion = BF4, CF3SO3, or Cl)

Abstract: Synthesis, spectroscopic characterisation, and single-crystal structure analyses are described for a number of CuI and CuII co-ordination compounds with the ligand 1,8-bis[bis(1′-methyl-benzimidazol-2′-ylmethyl)amino]-3,6-dioxaoctane (L). The compounds have the general formulae Cu2(L)X2Y2·xS, Cu(L)Y, Cu2(L)(CO)2Y2, Cu2(L)(Z)Y3, and Cu2(L)X2, where X = F, Cl, Br, or I; Y = ClO4, BF4, CF3SO3, Cl, or Br; Z = bridging anion like benzotriazolate; and S = solvent. Single-crystal structures of three CuII compounds, [Cu2(L)F2][BF4]2·2H2O·H2OBF3(1), [Cu2(L)Cl2]Cl2·6H2O (2), and [Cu2(L)Br2][CF3SO3]2·EtOH (3) have been determined using diffractometer data. All three compounds contain the dinuclear unit [XCu(L)CuX]2+ in which the ligand L bridges the two Cu–X fragments. However, the intramolecular Cu ⋯ Cu distances are very large (i.e. larger than 575 pm). The intermolecular Cu ⋯ Cu contacts are much shorter, being 481, 388–488, and 398–405 pm, for (1), (2), and (3), respectively. Ligand-field, e.s.r., n.m.r., and i.r. spectra have been used to characterise all the compounds. The ligand-field maxima all agree with square-pyramidal CuII with a CuN3XO chromophore in which X = F, Cl, or Br, respectively. The e.s.r. spectra indicate that exchange effects (intermolecularly) are important, resulting even in exchange-narrowed signals. Only the compounds Cu2(L)(Z)Y3 exhibit e.s.r. spectra typical for dinuclear CuII systems. The observed νCO bands at ca. 2 100 cm–1 for the CuI–CO adducts agree with end-on CO co-ordination.

Die Kristallstruktur von Mn2O7

Abstract: Mn 2 O 7 cristallise dans le systeme monoclinique, groupe d'espace P2 1/c et sa structure est affinee jusqu'a R=0,043

[Fe6Se9(SR)2]4− clusters (R=Me, CH2Ph): synthesis and characterization, and the X-ray structure of (PhCH2NEt3)4[Fe6Se9(SMe)2]

Abstract: (1) The compounds (PhCH2NEt3)4[Fe6Se9(SMe)2] and (Et4N)4[Fe6Se9(SCH2Ph)2] (2) have been isolated in good yields from Fe(SR)3 (R = Me, CH2Ph)/“Na2Se2” reaction mixtures in methanol/N,N-dimethylformamide after addition of the appropriate tetraalkylammonium chlorides. 1 is monoclinic, space group P21/c, Z = 4, with a = 18.697(14), b - 22.606(16), c = 15.989(11) Å, and β = 94.15(6)° at 140 K. Its structure has been refined to R (Rw) = 0.092 (0.075). The [Fe6Se9(SMe)2]4- anion contains six coplanar iron atoms which are present in distorted tetrahedral Se4 and Se3(SMe) ligand surroundings. The Se atoms are μ, μ3 and μ4 bridging. The four central Fe atoms and the Se atoms constitute a Fe4Se9 group that is structurally related to 1∞[Fe2Se3]2- double tetrahedral chains and 2∞[FeSe] layers. The Fe atoms in the [Fe6Se9(SMe)2]4- cluster are antiferromagnetically coupled. 1 has a room-temperature magnetic moment of 1.22 μB/Fe. Cyclic voltammograms, and electronic, infrared, and proton resonance spectra of 1 and 2 have been measured.

Über die Reaktion von W3O mit lod. Darstellung, Kristallstruktur und Eigenschaften von WOI3

Abstract: Die Darstellung des bisher unbekannten WOI3 gelingt, wenn man das in der Literatur auch als β-Wolfram bezeichnete Wolframoxid der Zusammensetzung W3O mit lod in einer Glasampulle im Temperaturgefalle (440–400°C) umsetzt. In der kalten Zone schlagt sich WOI3 in mausgrauen verfilzten Nadeln nieder. WOI3 kristallisiert tetragonal im NbOCl3-Typ in der Raumgruppe P42/mnm mit a = 12,346(2), c = 3,765(1) A (20°C). Die Kristallstruktur bei–130°C wurde aus Einkristall-Diffraktometerdaten bestimmt (R = 0,023). Ergebnisse der Messungen der magnetischen Suszeptibilitat und des Schwingungsspektrums sowie das beim Erhitzen von WOI3 erhaltene Massenspektrum werden angegeben. On the Reaction of W3O with Iodine: Preparation, Crystal Structure, and Properties of WOI3 The novel tungsten oxide iodide WOI3 is obtained from the reaction of the metalrich tungsten oxide W3O (also known as ‘β-tungsten’) with iodine in a sealed glass tube placed in a temperature gradient (440–400°C). In the low-temperature region WOI3 is formed as mouse-grey intergrown needle-like crystals. WOI3 crystallizes in the tetragonal NbOCl3 structure type, space group P42/mnm, with a = 12.346(2), c = 3.765(1) A (20°C). The crystal structure at – 130°C was determined from single-crystal diffractometer data (R = 0.023). Results of magnetic susceptibility and vibrational spectroscopic measurements are given together with the mass spectrum of WOI3 obtained on heating.

Specimen preparation of air sensitive materials for X-ray absorption measurements

Abstract: An improved technique for the preparation of solid specimens suitable for X-ray absorption measurements is described which is especially useful for air or water sensitive materials. The finely powdered materials are enclosed in a polymer matrix. Homogeneous, stable, and uniformly thick films can be obtained by this method. The capabilities of the technique have been tested within a series of iron and cobalt compounds.

Koordinationsverbindungen des Silber(I) mit stickstoffhaltigen Liganden Kristallstruktur des NC ? SCF2CF2S ? CN

Abstract: Die Reaktion von F2SNCN und NCSCF2CF2SCN mit AgAsF6 fuhrt zu den Koordinationsverbindungen (F2SNCN)2AgAsF62 und (NCSCF2CF2SCN)2AgAsF65. NCSCF2CF2SCN 3 entsteht sowohl bei der Reaktion von ClSCF2CF2SCl mit HCN als auch mit Me3SiCN.4 ist ein Nebenprodukt aus der Umsetzung mit HCN. 4 konnte als sechsgliedriger Heterocyclus charakterisiert werden. 3 wurde durch eine Einkristallrontgenstruktur-Analyse untersucht. Es liegt im festen Zustand in der all-trans Form vor. Coordination Compounds of Silver(I) with Nitrogen-Containing Ligands. Crystal Structure of NCSCF2CF2SCN The reaction of F2SNCN and NCSCF2CF2SCN with AgAsF6 leads to the coordination compounds (F2SNCN)2AgAsF62 and (NCSCF2CF2SCN)2AgAsF65. NCSCF2CF2SCN 3 is formed by the reaction of ClSCF2CF2SCl with HCN as well as with Me3SiCN. 4 is a by-product of the reaction with HCN. 4 was characterized as a six-membered heterocycle. 3 was investigated by an X-ray single structure analysis. In the solid state the all-trans form was found.

The Chemistry of 4-Substituted Oxazaphosphorinanes (OAP) (Tools for Cancer Research and Therapy)

Abstract: Novel chemical approaches resulted in 4-substituted OAP derivatives, linked by a sulfur, orygen or nitrogen atom to C-4. The cis- and trans-epimers were stereoselectively synthesized from the key intermediate 4-hydroxycyclophosphamide. An alternative route will be presented. The stereochemistry of 4-substituted OAP are confirmed by single crystal X-ray analysis and by NMR-spectra for more than 50 compounds. The connectivities of the nuclei observed in the homonuclear and heteronuclear COSY plots are summarized with data. In aqueous solution 4-substituted OAP are hydrolyzed with a half-life at physiological conditions of a few minutes for S-derivatives and of about 20 hours for the more stable N-derivatives. The pH-dependance of the hydrolysis rates including epimerisation and transthioacetalisation are submitted. Pharmacokinetical and biological activity data are presented.

Reaction of (Pentamethylcyclopentadienyl)(tert-butylimino)phosphane with Tris(acetonitrile)tricarbonylmolybdenum(0): Evidence for a Metalloiminophosphane Intermediate.

Abstract: (η1-Me5C5)P=N(t-Bu) (1) was prepared in a two-step synthesis from Me5C5PCl2. Reaction of 1 with (MeCN)3Mo(CO)3 affords the spirocyclic compound (η1-Me5C5PN(t-Bu)PN(T-Bu)C(O)Mo(CO)2(η5-C5Me5) (5), whose structure was determined by x-ray crystallography. A metalloiminophosphine, (η5-Me5C5)(CO)3MoP=N(t-Bu) (7), is proposed to be the key intermediate in the formation of 5.