Showing papers by "Bernt Krebs published in 1993"

Matrix‐assisted laser desorption/ionization mass spectrometry with additives to 2,5‐dihydroxybenzoic acid

Abstract: Selected benzoic acid derivatives and related substances were used as additives to 2,5-dihydroxybenzoic acid (2,5 DHB) and the performance of the mixtures in matrix-assisted laser desorption/ionization mass spectrometry was investigated. Using benzoic acid derivatives substituted at position 2 and /or 5 or related substances as a co-matrix in the 1-10% range with 2,5 DHB results in improved ion yields and signal-to-noise ratio of analyte molecules, especially for the high-mass range. The enhanced performance is prominent for 2-hydroxy-5 methoxybenzoic acid and exists for both proteins and oligosaccharides. It is suggested that the improvement is caused by a disorder in the 2,5 DHB crystal lattice allowing «softer» desorption. Charge transfer from matrix ions to additive molecules at the expense of analyte ionization gives a simple explanation for the deteriorating effects of some tested additives

Li5B7S13 und Li9B19S33: Zwei Lithiumthioborate mit neuen hochpolymeren Anionengerüsten†

Abstract: Li5B7S13 (C2/c; a = 17,304(2) A, b = 21,922(3) A, c = 12,233(2) A, β = 134,91(1)°; Z = 8 und Li9B19S33 (C2/c; a = 23,669(9) A, b = 14,361(3) A, c = 12,237(3) A, β = 103,77(2)°; Z = 4 wurden durch Reaktion von stochiometrischen Mengen Lithiumsulfid, Bor und Schwefel bei 750°C (Li5B7S13) und 700°C (Li9B19S33) mit anschliesendem Tempern dargestellt. Die Kristallstrukturen bestehen aus sich durchdringenden, polymeren Bor-Schwefel-Anionengerusten, die durch Eckenverknupfung von B4S10- und B10S20-Einheiten (Li5B7S13) bzw. B19S36-Einheiten (Li9B19S33) gebildet werden. Dazwischen befinden sich die Lithiumkationen, wobei bei Li9B19S33 eine starke Fehlordnung beobachtet wird. Li5B7S13 and Li9B19S33: Two Lithium Thioborates with Novel Highly Polymeric Anion Networks Li5B7S13 (C2/c; a = 17.304(2) A, b = 21.922(3) A, c = 12.233(2) A, β = 134.91(1)°; Z = 8) and Li9B19S33 (C2/c; a = 23.669(9) A, b = 14.361(3) A, c = 12.237(3) A, β = 103.77(2)°; Z = 4) were prepared by reaction of stoichiometric amounts of lithium sulfide, boron, and sulfur at 750°C (Li5B7S13) and 700°C (Li9B19S33) with subsequent annealing. The crystal structures consist of interpenetrating, polymeric boron sulfur anion networks which are formed by corner-sharing of B4S10 and B10S20 units (Li5B7S13), or B19S36 units (Li9B19S33). The lithium cations are situated in between with a strong disorder in Li9B19S33.

Die Perthioborate RbBS3, TIBS3 und TI3B3S10†

Abstract: Farblose, plattchenformige Kristalle von RbBS3 (P21/c, a=7,082(2) A, b=11,863(4) A, c=5,794(2) A, β=106,54(2)°) entstehen aus einem stochiometrischen Ansatz von Rubidiumsulfid, Bor und Schwefel bei 600°C und anschliesendem Tempern. Die zu RbBS3 isotype Phase TlBS3 (P21/c, a=6,874(3) A, b=11,739(3) A, c=5,775(2) A, β=113,08(2)°) erhalt man aus dem Ansatz Tl2S · 2 B2S3. Das nach 7 h bei 850°C erhaltene glasige Produkt wird in einem Zweizonenofen 400 h bei 400350°C ausgelagert. Gelbe Kristalle der Verbindung bilden sich in der warmeren Ofenzone. Das ebenfalls gelbe Tl3B3S10 (P1, a=6,828(2) A, b=7,713(2) A, c=13,769(5) A, α=104,32(2)°, β=94,03(3)β, γ=94,69(2)°) bildet sich aus stochiometrischen Mengen von Thalliumsulfid, Bor und Schwefel bei 850°C und anschliesendem Tempern. Die ausschlieslich tetraedrisch koordiniertes Bor enthaltenden Verbindungen bilden polymere Kettenstrukturen, die sich im Fall des RbBS3 und TlBS3 aus spirocyclisch uber die Boratome verknupften, nichtplanaren Trithiadiborolan-Ringen aufbauen. Ersetzt man in diesen Anionenketten jeden dritten B2S3-Funfring durch einen B(S2)2B-Sechsring, so erhalt man die Anionenstruktur des Tl3B3S10. The Perthioborates RbBS3, TIBS3, and Tl3B3S10. RbBS3 (P21/c, a=7.082(2) A, b=11.863(4) A, c=5.794(2) A, β=106.54(2)°) was prepared as colourless, plate-shaped crystals by reaction of stoichiometric amounts of rubidium sulfide, boron, and sulfur at 600°C and subsequent annealing. TlBS3 (P21/c, a=6.874(3) A, b=11.739(3) A, c=5.775(2) A, β=113.08(2)°) which is isotypic with RbBS3 was synthesized from a sample of the composition Tl2S · 2 B2S3. The glassy product which was obtained after 7 h at 850°C was annealed in a two zone furnace for 400 h at 400350°C. Yellow crystals of TlBS3 formed at the warmer side of the furnace. Tl3B3S10 (P1, a=6.828(2) A, b=7.713(2) A, c=13.769(5) A, α=104.32(2)°, β=94.03(3)°, γ=94.69(2)°) was prepared as yellow plates from stoichiometric amounts of thallium sulfide, boron, and sulfur at 850°C and subsequent annealing. All compounds contain tetrahedrally coordinated boron. The crystal structures consist of polymeric anion chains. In the case of RbBS3 and TlBS3 nonplanar five-membered B2S3 rings are spirocyclically connected via the boron atoms. To obtain the anionic structure of Tl3B3S10 every third B2S3 ring of the polymeric chains of MBS3 is to be substituted by a six-membered B(S2)2B ring.

Preparation, structure and properties of dinuclear, trinuclear incomplete cuboidal and cuboidal molybdenum-selenium cluster complexes

Abstract: Preparation of the di-µ-selenido-dimolybdenum(V) complex [Mo2O2(µ-Se)2(cys)2]2–(cys =L-cysteinate dianion), and the related aqua ion [Mo2O2(µ-Se)2(H2O)6]2+, has enabled the trimolybdenum(IV) incomplete cuboidal Mo3OxSe4–x4+(x= 0–3) complexes [Mo3(µ3-Se)(µ-Se)3(H2O)9]4+[Mo3(µ3-Se)-(µ-O)(µ-Se)2(H2O)9]4+, [Mo3(µ3-Se)(µ-O)2(µ-Se)(H2O)9]4+, and the mixed-valence (average oxidation state 3.25) cuboidal [Mo4(µ3-Se)4(H2O)12]5+ complex to be obtained for the first time. The crystal structures of Na[NMe4][Mo2O2(µ-Se)2(cys)2]·7H2O, [NMe4]5-(pts)5·14H2O (pts–= toluene-p-sulfonate) have been determined. Electrolytic reduction of [Mo4(µ3-Se)4(H2O)12]5+ in 2 M Hpts gives quantitatively the air-sensitive tetramolybdenum(III) analogue [Mo4(µ3-Se)4(H2O)12]4+(Ef°= 190 mV). Similarly the 5+ ion can be oxidised to the 6+ state (Ef°= 790 mV). Compared to analogous Mo-S clusters, Mo-Se clusters exhibit identical structures but with longer bond distances, red-shifted absorption bands, and in the case of the cuboidal aqua complexes less-positive reduction potentials. By analogy with [Mo3S4(H2O)9]4+, [Mo3MSe4(H2O)10]4+ heterometal cuboidal and related complexes are obtained. The edta(=N,N,N′N′-ethylenediamine-tetraacetate) complex of the 5+ cube [Mo4Se4(edta)2]3– has been prepared, and reduction potentials for the corresponding core 5+/4+ and 6+/5+ couples determined as –40 and 650 mV respectively.

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

Reaktive E=C(p-p)π-Systeme. XXXIII: Side-on-Koordination des Phosphaalkins P≡C-N(iPr)2 im 16e-Nickel(0)-Komplex Ni(CO)PCy3[PCN(iPr)2]

Abstract: Reactive E = C(p-p)π Systems, XXXIII. — Side-on Coordination of the Phosphaalkyne P ≡ C — N(iPr)2 in the 16e Nickel(0) Complex Ni(CO)PCy3[PCN(iPr)2] The reaction of (diisopropylamino)phosphaethyne P ≡ C — N(iPr)2 with the nickel complex [Ni(CO)3PCy3] – in contrast to the analogous reactions with Ni(CO)4 or Ni(CO)3PR3 (R = Me, Ph) – leads to the novel 16e nickel(0) system [Ni{η2-P ≡ C — N(iPr2)}(CO)PCy3] with a planar geometry of all skeleton atoms besides the methyl and cyclohexyl groups. Side-on coordination of the P ≡ C triple bond results in an increase of the PC distance to 1.665 Ȧ typical for phosphaalkenes.

Synthese und Kristallstruktur einer Neuen hexagonalen Modifikation von Al2S3 mit fünffach koordiniertem Aluminium

Abstract: Eine bisher noch nicht beschriebene hexagonale Hochtemperatur-Modifikation von Al2S3 konnte in reiner Form entweder durch chemischen Transport mit Iod (860 → 750°C) oder durch Tempern von α -Al2S3 oberhalb 550°C erhalten und durch eine Einkristall-Rontgenstrukturanalyse charakterisiert werden. Die neue Form des Al2S3 kristallisiert in der Raumgruppe P 61 (Nr. 169) mit a = 6,491(1), c = 17,169(4) A, V = 626,5 A3, Z = 6; R = 0,0253. In dieser Modifikation liegt die eine Halfte der Aluminiumatome tetraedrisch koordiniert vor [d(AlS): 2,226–2,267 A], wahrend die andere Halfte trigonal-bipyramidal von funf S-Atomen mit AlS-Bindungslangen von 2,272 bis 2,315 A (aquatorial) und 2,495–2,521 A (axial) umgeben ist. Aluminium in AlS5-Koordination ist bisher unbekannt und wird hier zum ersten Mal beobachtet. Die Struktur ist isotyp zu In2Se3 und AlInS3. Zusatzlich wird uber die Verfeinerung der Kristallstruktur α von -Al2S3 an Einkristallen berichtet, die ebenfalls durch chemischen Transport mit Iod hergestellt wurden.

Synthesis and structural chemistry of novel heteropolymolybdates and -tungstates

Abstract: The chemistry of polynuclear oxometalate anions is dominated by molybdenum and tungsten in their highest oxidation state. During the past twenty years this class of compounds has attracted much attention because of their variable applications, e.g. as reagents in analytical procedures, as industrial catalysts and as potential anticancer drugs.

Zink-Koordinationsverbindungen mit Imidazolin- und Imidazol-Donorliganden

Abstract: Durch Umsetzungen der zweizahnigen Bisimidazolin-Liganden 1,2-Bis(2-imidazolin-2-yl)ethan (BIE) und 1,2-Bis(2-imidazolin-2-yl)benzol (BIB) mit Zinkbromid unter verschiedenen Reaktionsbedingungen konnten die Komplexverbindungen [ZnBr2(BIE)] (1), [ZnBr2(BIB)] (2), [Zn(BIE)2]Br2 (3) und [Zn(BIB)2](BPh4)2 (4) synthetisiert und charakterisiert werden. Das Zinkatom ist jeweils tetraedrisch von einem zweizahnigen Chelatliganden und zwei Bromatomen oder von zwei dieser Liganden koordiniert. Die ZnN-Bindungslangen in 1–4 variieren zwischen 1,966(2) und 2,013(3) A, fur die ZnBr-Abstande wurden Werte zwischen 2,372(1) und 2,403(1) A beobachtet. Mit dem neuen Liganden [3-(Imidazol-1-yl)-1-oxopropyl]benzol (IOB) gelang die Synthese des Komplexes [ZnCl2(IOB)2] (5), in dem eine tetraedrische ZnN2Cl2-Koordinationseinheit vorliegt (ZnN: 2,013(3) und 2,029(2) A; ZnCl: 2,226(1) und 2,242(1) A). Die farblosen Verbindungen 1–5 wurden durch IR-, 1H-NMR- und Rontgenabsorptionsspektren sowie durch vollstandige Rontgenstrukturanalysen charakterisiert. Raumgruppen und Gitterkonstanten: 1: P21/c, a = 7,717(2), b = 22,814(5), c = 8,026(2) A, β = 117,58(2)° (140 K), R = 0,0283; 2: Cc, a = 11,831(3), b = 11,677(1), c = 11,846(1) A, β = 114,55(2)°, R = 0,0237; 3: P42/n, a = 7,931(1), c = 16,945(1) A, R = 0,0312; 4: P21/c, a = 18,666(2), b = 16,615(2), c = 19,786(2) A, β = 99,17(1)°, R = 0,0472; 5: P21/c, a = 9,173(2), b = 9,230(1), c = 28,357(3) A, β = 96,63(1)°, R = 0,0317. Zinc Coordination Compounds with Imidazoline and Imidazole Donor Ligands. By reaction of the two bidentate bisimidazoline ligands 1,2-bis(2-imidazoline-2-yl)ethan (BIE) and 1,2-bis(2-imidazoline-2-yl)benzene (BIB) with zinc bromide under various reaction conditions the complexes [ZnBr2(BIE)] (1), [ZnBr2(BIB)] (2), [Zn(BIE)2]Br2 (3) and [Zn(BIB)2](BPh4)2 (4) were synthesized and characterized. In all compounds the zinc atom is tetrahedrally coordinated, either by a bidentate ligand and two bromine ligands, or by two of the chelate ligands. ZnNbond distances for 1–4 range from 1.966(2) to 2.013(3) A, and the ZnBr distances from 2.372(1) to 2.403(1) A. [3-(imidazole-1-yl)-1-oxopropyl]benzene (IOB) was prepared as a novel imidazole ligand which carries a keto-O atom in 1,5-position to the pyridine-N atom. The zinc in [ZnCl2(IOB)2] (5) is coordinated by two ligands and two Cl atoms forming a distorted tetrahedral ZnN2Cl2 unit (ZnN: 2.013(3) and 2.029(2) A; ZnCl: 2.226(1) and 2.242(1) A). The colourless compounds 1–5 were characterized by IR, 1H-NMR, X-ray absorption spectra and single-crystal X-ray structure analysis. Space groups and structural data: 1: P21/c, a = 7.717(2), b = 22.814(5), c = 8.026(2) A, β = 117.58(2)° (140 K), R = 0.0283; 2: Cc, a = 11.831(3), b = 11.677(1), c = 11.846(1) A, β = 114.55(2)°, R = 0.0237; 3: P42/n, a = 7.931(1), c = 16.945(1) A, R = 0.0312; 4: P21/c, a = 18.666(2), b = 16.615(2), c = 19.786(2) A, β = 99.17(1)°, R = 0.0472; 5: P21/c, a = 9.173(2), b = 9.230(1), c = 28.357(3) A, β = 96.63(1)°, R = 0.0317.

Reaktive E=C(p–p)π-Systeme, XXXVI [1] Darstellung, Reaktivität und Ligandeneigenschaften des Trifluormethyl-1,3-diphosphans tBu(H)PCF2P(H)CF3 / Reactive E=C(p—p)π Systems, XXXVI [1]. Synthesis, Reactivity and Ligand Properties of the Trifluoromethyl-1,3-diphosphane tBu(H)PCF2P(H)CF3

Abstract: Trifluoromethyl-1,3-diphosphane tBu(H)PCF₂P(H)CF₃ (2) is formed regioselectively in almost quantitative yield by addition of tert-butylphosphane to perfluoro-2-phosphapropene F₃CP=CF₂ (1) as a 1:1 mixture of two diastereomers 2 a and 2b. 2 reacts with nickel tetracarbonyl to give the binuclear complex [tBu(H)PCF₂P(H)CF₃Ni(CO)₂]₂ (3) as the only isolable product. The mixture contains four of the eight possible isomers; one of them (3 a) could be isolated in pure form by crystallization from n-pentane solution. Attempts to generate the phosphaalkene tBu(H)PC(F)=PCF₃ or the 1,3-diphosphaallene tBuP=C=PCF₃ by HF elimination from 2 with NEt₃, HNMe₂ or HNEt₂ lead to complicated mixtures of products. On the other hand, reaction of 3 a with isopropylamine affords the binuclear complex [(CO)Ni(F₃CP=CFP(H)tBu)Ni(CO)₂tBu(H)PCFHP(CF₃)NHiPr] (4) with both a 16 eand an 18 e-nickel(O) fragment and a side-on coordinated F₃CP=CF group. The new compounds were characterized by spectroscopic investigations, 3 a and 4 by an X-ray diffraction study.

Reaktive E=C(p-p)π-systeme. XXXVI: Darstellung, Reaktivität und Ligandeneigenschaften des Trifluormethyl-1,3-diphosphans tBu(H)PCF2P(H)CF3

Abstract: Trifluoromethyl-1,3-diphosphane tBu(H)PCF 2 P(H)CF 3 (2) is formed regioselectively in almost quantitative yield by addition of tert-butylphosphane to perfluoro-2-phosphapropene F 3 CP=CF 2 (1) as a 1:1 mixture of two diastereomers 2a and 2b. 2 reacts with nickel tetracarbonyl to give the binuclear complex [tBu(H)PCF 2 P(H)CF 3 Ni(CO) 2 ] 2 (3) as the only isolable product. The mixture contains four of the eight possible isomers; one of them (3a) could be isolated in pure form by crystallization from n-pentane solution