Biscyclopentadienides with transition metal-mercury bonds. II: Dithiocarbamato derivatives of molybdenum and tungsten,and X-ray structure of (η5-C5H5)2Mo[HgS2CN(C2H5)2]2

The reactions in THF or benzene between Cp₂ M (HgX)₂ ·x HgX ₂ (M = Mo or W; O ?x ? 1;X ^? = Cl^?, Br^?, I^?, SCN^?, OAc^?) and sodium diethyl-dithiocarbamate $$\begin{gathered} Cp_2 M\left( {HgX} \right)_2 .xHgX_2 + \left( {2 + x} \right)Nadtc \rightleftharpoons Cp_2 M\left( {Hgdtc} \right)_2 \hfill \\ + xHg\left( {dtc} \right)_2 + \left( {2 + x} \right)NaX \hfill \\ \end{gathered} $$ as well as between Cp₂ MH₂ and mercury diethyldithiocarbamate $$x2Cp_2 MH_2 + 2Hg\left( {dtc} \right)_{2 - } Cp_2 M\left( {Hgdtc} \right)_2 + \left\{ {Cp_2 Mdtc} \right\}dtc + 2H_2 $$ give the compound Cp₂ M(Hgdtc)₂ (dtc is diethyldithiocarbamate anion). The structure of the molybdenum complex determined by the X-ray method (a = 12.776(4),b = 7.835(4),c = 27.397(7) Å β = 111.18(2) °; space groupC2/c (No. 15);Z = 4) consists of discrete molecules occupying special positions on two-fold axes. A short Mo-Hg distance of 2.643(8) Å and a rather long Hg-S one of 2.50(2) Å were found. The diethyldithiocarbamate anion behaves like a monodentate ligand. IR and¹H,¹³C NMR results agree with the molecular structure determination and confirm a weak bond between mercury and dithiocarbamate and strong molybdenum-mercury bond. A considerable solvent effect (C₆D₆ vs. CDCl₃ solutions) has been observed on the¹H chemical shifts of both dtc and Cp ligands. The {Cp₂Modtc}⁺ X ^? (X = dtc and PF₆) complexes, although not obtained in a pure form, were included in the discussion of the spectroscopic features of those with theM-Hg bonds.     

Projet de l'ensemble critique uranium enrichi-eau légère crocus

Sans résuméSubsides N^o 4353 et N^o 4779.2 du Fonds national suisse de la recherche scientifique.     

Nouvelles voies d'acces aux phospha-7-norbornenes trivalents

New λ³-7-phosphanorbornenes are prepared either through the nickelocene reduction-complexation of the corresponding P-sulfides ($\text{syn}$ structure) or through the direct [14 + 2] cycloaddition of tervalent phospholes with N-phenylmaleimide ($\text{anti}$ structure).     

New Zealand Developments in Earth's Field NMR

We review here two decades of development of Earth's field nuclear magnetic resonance (NMR), starting with the first demonstration of resonant refocusing and the generation of spin echoes, the first measurement of diffusion using Earth's field NMR, and its application to Antarctic research, the adaptation of the apparatus to allow its use indoors, in a conventional laboratory setting, and finally, the construction of a flexible laboratory-based Earth's field NMR system capable of not only a range of relaxation and spectroscopy applications but also the straightforward demonstration of NMR Imaging. Authors' address: Paul T. Callaghan, MacDiarmid Institute, Victoria University of Wellington, PO Box 600, Wellington, New Zealand     

Verification of gamma spectroscopy programs: Multiplet area problems and solutions

In this work we demonstrate that the latest addition to the Canberra/Nuclear Data family of software packages, Genie-PC, performs as well as or better than the older software packages with respect to the doublet tests reported on earlier. In addition, we demonstrate the behavior of the various software packages for a doublet which includes the 511 keV annihilation line. And we show that using other means to break a doublet into its component areas will also lead to accurate overall results.     

On the asymptotic behaviour of sums Σg(n){x/n} k

In this paper we estimate the difference between the sum given in the title (whereg(t) is an arbitrary real-valued non-decreasing function,k is a positive integer and summation is extended over all positive integersnx) and the corresponding integral, obtaining the boundO(g(x)x ^1/3logx). Furthermore, we show that these differences (for giveng and varyingk) are all approximately equal, with an error term ofO(g(x)x ^3/10). Finally it is remarked without proof that these estimates can be refined toO(g(x)x ) (with any >0,329...) resp.O(g(x)x ^109/382).     

Sensitive gas chromatographic methods for the determination of vinyl epoxide synthetase activity using trichloroethylene as a model substrate

Two specific and very sensitive methods for the determination of vinyl epoxide synthetase activity in liver microsomes are described. Trichloroethylene, which is used as a substrate, is converted into trichloroethylene oxide by a hepatic epoxide synthetase. Chloral hydrate, the final rearrangement product of trichloroethylene oxide, is determined by electron-capture gas chromatography, either after derivatization with pentafluorophenylhydrazine or after its conversion into chloroform under alkaline conditions. The kinetic parameters of the epoxidation reaction were determined on rat hepatic microsomal suspensions.     

Analogies Photochimiques. III—Diméthyl-4,4 allyl-2 Cyclohexanone. Elimination Inattendue de C2H4O et Perte de 15 Unités de Masse

The mass spectrum of 4,4-dimethyl 2-allyl cyclohexanone shows an ion at m/z 122 resulting from the elimination of a neutral acetaldehyde molecule direct from the molecular ion. Deuterium labelling results show a complex decomposition pathway during which four hydrogen atoms transfer to the eliminated acetaldehyde molecule. The molecular ion of this compounds also loses a methyl group originating from the allyl substituent. The mechanisms are discussed in terms of photochemical analogies.