Borohydride complexes, volatility

The quality characteristics for an inhomogeneous sample can be improved by complexing with ethylenediamine-iV,V,iV, iV -tetraacetate (EOTA) after reaction. The antimony compound is converted to stibine with sodium borohydride. The volatile metallic hydride is transferred with helium to a heated quartz cuvette at the beam entrance of an atomic absorption spectrometer. There the hydride is thermally decomposed at 900°C and the antimony is determined by AAS. Calibration is carried out by the addition of standards. 

The most useful chemical species in the analysis of arsenic is the volatile hydride, namely arsine (AsH3, bp -55°C). Analytical methods based on the formation of volatile arsines are generally referred to as hydride, or arsine, generation techniques. Arsenite is readily reduced to arsine, which is easily separated from complex sample matrices before its detection, usually by atomic absorption spectrometry (33). A solution of sodium borohydride is the most commonly used reductant. Because arsenate does not form a hydride directly, arsenite can be analyzed selectively in its presence (34). Specific analysis of As(III) in the presence of As(V) can also be effected by selective extraction methods (35). 

SYNTHESIS A well-stirred solution of 1.77 g 2,5-dimethoxy-B-nitro-4-(n-propylthio)styrene (see under 2C-T-7 for its preparation) in 20 mL anhydrous THF was placed in an He atmosphere and treated with 1.5 mL of 10 M borane-dimethyl sulfide complex. This was followed by the addition of 0.2 g sodium borohydride, and the stirring was continued at room temperature for a week. The volatiles were removed under vacuum, and the residue was treated with 20 mL dilute HC1 and... 

The hydride complexes of actinides usually contain a coligand, such as, for example, OR, dmpe, or Cp, and can be monomeric or oligomeric. Thus, the borohydrides An(BH4)4 produced according to (5.68) are polymeric (An = Th, U) or monomeric (An = Np, Pu), whereas the An(BH3Me)4 are all monomeric. Their volatility increases from Th to Pu, whereas their stability goes in the opposite direction [282] ... 

In addition to these, a number of other complexes have been isolated, such as the f-diketonates [Pa(PhCOCHCOPh)4] and antiprismatic [Pa(MeCOCHCOMe)4], which, like the TTFA complex [Pa(C4H3SCOCHCOCF3)4], are soluble in solvents like benzene, and suitable for purification by solvent extraction. Pa forms a volatile borohydride [Pa(BH4)4]. These compounds are typical of those formed by other early actinides, such as Th and U. 

The Zr and Hf tetrahydroborates M(BH4)4 are the most volatile compounds of these elements, with boiling points of 123 and 118°C they are also very sensitive to oxidation and hydrolysis. They can be obtained by the reaction of the chlorides with alkali metal borohydrides or of the complex fluorides NaMFs with aluminum borohydride (the fluorides MF4 do not react), followed by distillation from the reaction mixture. According to low-temperature X-ray data, all the borohydride groups are tridentate in both M(BH4)4 complexes, which have Td symmetry. The same is trae for their substituted M(BH3Me)4 derivatives, that is, the metal atom is 12-coordinate. Proton NMR indicates fast exchange of bridging and terminal protons on the NMR timescale in these fluxional molecules see Fluxional Molecule). 

A 25-mL solution containing 500 ppb of arsenic (Ag3+) was stirred with 1 g of borohydride-form A-26 anion-exchange resin. The reaction vessel was connected to an absorption tube filled with a solution to absorb the volatile hydride of arsenic (i.e., arsine, AsH3). The absorption solution is made by dissolving 1 g of silver diethyldithiocarbamate (SDDC) in 200 mL of pyridine. The volatile arsine is complexed with the SDDC solution to give a colored solution, whose absorbance is... 

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