A new family of heavy transition metal coordination compounds and its application,I. Design,synthesis and characterization of volatile organohafnium precursors

The first three representatives of a new family of volatile organohafnium compounds suitable as metallo-organic chemical vapour deposition precursors were synthesized. A combination of cyclopentadienyl and alkoxo-ligands with a bicyclo[2.2.1]heptanc framework was used. Volatility at relatively low temperatures for hafnium compounds was found and the precursors were characterized by elemental analysis and spectroscopic methods (IR, ¹H and ¹³C NMR, mass spectrometry and mass-analysed ion kinetic energy spectroscopy). The outlook for use in hafnium functional materials synthesis was derived from the fragmentation data.     

Facile high-yield synthesis of pure, crystalline Mg(BH4)2

Magnesium borohydride, Mg(BH4)2, a long-sought candidate for efficient hydrogen storage chemisorption technology, has been obtained in a pure and crystalline form by two new synthetic routes in a hydrocarbon solvent. A first synthetic approach involves a metathetical reaction between organometallic magnesium compounds; a second route consists of an insertion reaction of BH3 species, released from BH3.S(CH3)2, into the Mg-C bonds of MgR2, with complete replacement of R groups with BH4 groups. Both methods, based on commercially available reagents, afford identical, pure, polycrystalline materials, identified by X-ray diffraction as the so-called low-temperature hexagonal form of Mg(BH4)2, stable below 180 degrees C, recently shown to possess a complex, unpredictable, crystal structure.     

Alysis of the volatile constituents of food by headspace GC-MS with reversal of the carrier gas flow during sampling

A technique has been developed for performing headspace GC-MS analysis of volatile components of food, in which the carrier gas flow is reversed during sampling in order to overcome problems caused by the diffusion of substances not retained by the cold trap. Chromatographic profiles of volatile compounds from cheeses, obtained at room temperature, provide confirmation of the validity of the reversed flow technique, and the versatility of the system is evidenced by its successful application to both solid and liquid matrixes: the absence of any discrimination against the various components reveals its efficacy for compounds with a wide range of volatility. Addition of internal standards to the sample enables the use of the technique for quantitative analysis.     

Photoelectron spectroscopy of actinide organometallic compounds I. Bis(cyclooctatetraene)actinide(IV) complexes

The He(I) photoelectron spectra of the antinocene species Th(cot)₂ and U(cot)₂ (cot = cyclooctatetraene) have been determined. The 5f metal ionization has been detected at the onset of the uranocene spectrum. The low ionization energy region of both spectra is discussed in terms of simple qualitative molecular orbital scheme.     

The chloro­(diethyl­amino)­di­methyl­tin dimer

The title compound, di‐μ‐diethyl­amido‐N:N‐bis­[chloro­di­methyl­tin(IV)], consists of discrete [Sn₂Cl₂(CH₃)₄(C₄H₁₀N)₂] dimer mol­ecules, with Sn atoms linked by bridging diethyl­amido groups. The coordination geometry about the metal atom is distorted trigonal bipyramidal, with the two methyl C atoms and one N atom in the equatorial plane, and the Cl and second N atom in axial positions.     

Tomographic images improved by holographic synthesis

A holographic technique is used to combine the information content of conventional, 2D tomographic scan images into a full-parallax, 3D reconstruction of the recorded subject. Advantages of the system over the conventional, pseudo-3D reconstructions obtained by computer image processing, or over the direct examination of the scan images by the physician, are a more realistic and detailed information to the observer, as true parallax and physical depth cues are fully maintained.     

Volatile enrichment on automatic static headspace using a precolumn and stopping the carrier gas flow during injection

The aim of this study was to develop a technique for performing automatic static headspace analysis of volatiles without a cryogenic device. Reconcentration of solutes was accomplished using a graphitized carbon coated precolumn between two splitting points and stopping carrier gas flow during injection. Chromatographic profiles of volatile compounds from ground coffee compared with split and splitless injections provide confirmation of the good sensitivity of the technique. The analysis of a standard mixture covering a wide range of volatility confirms that the described technique might be useful to achieve enrichement of low volatile headspace compounds, even if discrimination against the various components is present.     

Potentiometric titrations of organotin chlorides with tetraphenylarsonium chloride in acetonitrile media

Tetraphenylarsonium chloride was used for the potentiometric titration of R₄-_nSnCl_n compounds (R = Me, Et, Pr, Bu, Ph ; n = 2,3) in acetonitrile media. Evidence for penta-coordinated R₄-_nS_nCl_n+1- complexes was obtained. A stability scale as a function of R groups is given.     

Solution dynamics and molecular structure elucidation of novel aluminium derivatives containing diaminodimethylsilane ligands

The interaction of dimethyldiaminosilane ligands of general formula SiMe2(NR2)(NR'2)(NR2, NR'2 = NiHPr, NHtBu, NC4H8, NHCH2CH2NMe2) with AlX3 (X = Cl, Me) has been investigated and the synthesis of novel aluminium derivatives is reported, namely AlMe3[SiMe2(NR2)(NR'2)], AlX2[SiMe2(NR)(NR'2)] and AlMe[SiMe2(NR)2], containing the silane ligand as neutral, monoanionic and dianionic species, respectively. Moreover, the solution molecular structures and dynamics have been elucidated via 1D/2D variable temperature NMR spectroscopy showing the influence of the N-substituents of the silane ligand and of the aluminium ancillary ligands.     

The transacetalization reaction during the etherification of poly(oxymethylene)diol [α-hydro-ω-hydroxypoly(oxymethylene)] with orthoesters in the presence of lewis acids

A transacetalization reaction occurs during the etherification of poly(oxymethylene)diol [α-hydro-ω-hydroxypoly(oxymethylene)] with orthoesters and an important modification of molecular structure takes place. The intermediates formed during the transacetalization reaction are emphasized. The connection between this reaction and the other reactions during the etherification of poly(oxymethylene)diols is discussed.