Showing papers by "Bernt Krebs published in 1990"

Developments in chalcogen-halide chemistry

Abstract: Publisher Summary This chapter presents an account of the current preparative and structural aspects of chalcogen-halide chemistry. The chapter focuses on the inorganic chemistry of the binary chlorides, bromides, and iodides as well as on the corresponding hypervalent anionic and cationic halo derivatives; fluorides are referred to in only a few cases. The chapter discusses the variability of the structural and bonding properties of the “inert pair” systems of the chalcogens in their formally lower positive oxidation states that directly influences the reactivity and the nature of the variety of possible reaction products. This field of chemistry may serve as a model for bonding, structure, and the reactive properties of analogous s2 systems of the neighboring elements, such as Sb(III), Bi(III), or I(V). Current investigations, for example, on antimony(III) and arsenic(III) halogen compounds, have indicated quite similar structural principles as in Te(IV) analogues. In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride and of tellurium tetrachloride on twinned crystals were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties, as well as the synthetic potential of the compounds. The chapter discusses the characteristic structural and bonding features of the halogen compounds of the chalcogen(IV) systems, in which the role of the inert pair determines much of the stereochemistry and reactive properties of the whole class of compounds. SCl4, as the only stable tetrahalide of sulfur besides SF4, is known to be easily prepared at temperatures below –34°C from the elements or from the reversible reaction of equimolar amounts of SC12 and chlorine.

Selenoarsenate aus wäßriger Lösung. Die Kristallstruktur von Na3AsO3Se · 12 H2O und Na3AsSe4 · 9H2O†

Abstract: Die aus wasriger Losung durch Reaktion von As2O3 mit NaOH und Selen (oder durch Umsetzung von Na2Se mit As2Se3 und Selen) unter strengem Sauerstoffausschlus zuganglichen farblosen kristallwasserhaltigen Selenoarsenate enthalten neben den tetraedrischen Anionen AsO3Se3− und AsSe43− Wasserstoffbrucken-Systeme mit strukturbestimmenden OH … Se- Brucken. Na3AsO3Se · 12 H2O kristallisiert in P212121 mit a = 9,220(3), b = 13,018(3), c = 14,048(4) A, Z = 4. Das kubische Na3AsSe4 · 9 H2O (P213, a = 12,149(3) A, Z = 4) ist isotyp mit dem Schlippeschen Salz Na3SbS4 · 9 H2O. Die Se2− in AsO3Se3− und AsSe43− sind H-Acceptoren in jeweils 6 Se … HO-Wasserstoffbrucken mit d(Se…O) = 3,693 A und d(Se…H) = 2,47–2,89 A. Die AsSe-Bindung in AsO3Se3− (2,283 A) ist kurzer als bei AsSe43− (2,319 A).

Preparation, structure, and properties of the Mo/Se ions [Mo2O2(µ2-Se)2(H2O)6]2+ and [Mo4(µ3-Se)4(H2O)12]5+

Abstract: Preparation of the MoV2 di-µ-selenido aqua ion, [Mo2O2(µ2-Se)2(H2O)6]2+, has enabled the cuboidal mixed-valence (3.25) ion [Mo4(µ3-Se)4(H2O)12]5+ to be obtained; characterisation of both complexes including crystal structures of Na(Me4N)[Mo2O2(µ2-Se)2(Cys)2]·7H2O [Cys =L(+)-cysteine] and [Mo4(µ3-Se)4(H2O)12](MeC6H4SO3)5·14H2O have been carried out and are reported.

Natural product chemistry, part 100: The structure of carissone, C 15 H 24 O 2

Abstract: C15H24O2,M=236.2, monoclinic, P 21,a=7.229(7),b=14.925 (9),c=6.235 (9) A, β=92.40 (9)°,V=672.1 A3,T=−133 °C,Z=2,D x=1.17 g cm−3. The X-ray diffraction analysis of this sesquiterpenoid fromCarissa opaca confirmed the previously proposed constitution of the isolate and, furthermore, allowed precise NMR assignment.

Preparation, Structure, and Properties of Manganese Toluene-3,4-dithiolate Complexes in Different Oxidation States.

Abstract: in acetonitrile, a Hammett plot showed a linear relationship between Hammett u, values and the second reduction potential, indicating that electron density changes on the ligand are transmitted to the metal ions.'O Replacement of the 4-methyl ring substituent by CF3 in I and I1 has been shown to increase Elp for both one-electron-reduction steps in DMF by 0 . 1 4 4 1 9 V, clearly indicating the transmission of a distant electron-withdrawing effect to the copper centers." The wide separation of the two reduction waves of all these compounds indicates significant stability for the one-electron intermediates, as is indicated by the large conproportionation constants (Table VII). The one-electron-reduced species derived from I exhibits a seven-line EPR spectrum at room temperature in both CH2C12 and CH3CN, indicative of interaction of the odd electron with both copper Compound I1 produces a one-electron-reduced species in CH3CN, which also exhibits a seven-line spectrum (Figure 6). The analogous copper tetrafluoroborate complex involving the butylene-bridged macrocyclic ligand derived from 4-tert-butyl-2,6-diformylphenol has also been shown to produce a one-electron-reduced species in CH2C12 or acetone, which exhibits a seven-line spectrum at room temperature." This behavior contrasts with that associated with I11 and IV, which exhibit four-line ~pectra.~*~O Acknowledgment. We thank the Natural Sciences and Engineering Research Council of Canada for financial support for this study, including the purchase of the variable-temperature Faraday susceptometer and EPR spectrometer.