Boron hydrides spectroscopy

Boron s electron deficiency does not permit conventional two-electron bonds. Boron can form multicenter bonds. Thus the boron hydrides have stmctures quite unlike hydrocarbons. The B nucleus, which has a spin of 3/2, which has been employed in boron nuclear magnetic resonance spectroscopy. 

MetalIa-/3-diketonate complexes, such as 1, are conveniently prepared by reacting acylmetal carbonyl complexes with strong bases that can also react as nucleophiles, such as organolithium, Grignard, or boron hydride reagents [Eq. (1)]. These reactions can be followed by IR spectroscopy. 

The three-centered, two-electron hydride bridge, which is prevalent in boron hydride chemistry, has been very well characterized in the ir and Raman spectroscopy of diborane and certain metal borohydrides. A brief review of these data will be given at this point because they afford insight into hydride-bridged systems. 

Another complex hydride, A1(BH4)3 (9), a colorless liqnid (mp -64.5 °C, bp 44.6 °C), was the first componnd demonstrated to be flnxional (see Fluxional Molecule). Its thermal decomposition also led to the first componnd to be discovered and structurally characterized by NMR spectroscopy, AI2B4H18 (10). Reaction of A1(BH4)3 with a variety of boranes produces compounds analogous to boron hydride clusters such as AIB4H u, AIB5 H11, AIB5 H12, A1B6Hi2, and AlBeHn (seeBoron Hydrides) ... 

The correct structure of B2H6 was determined by infrared spectroscopy, and this was the only boron hydride structure simple enough to be determined by this means. The actual B2H6 structure is... 

Infrared spectroscopy has assisted in the determination of the structure of certain complex inorganic molecules, uch as the metal carbonyls, inter-halogen compounds, boron hydrides, and nitrogen oxides. The practice used has been to compare the observed spectrum with the spectrum expected for an assumed model on the basis... 

Cyclization of enone (9) in hexane with boron trifluorideetherate in presence of 1,2-ethanedithiol, followed by hydrolysis with mercury (II) chloride in acetonitrile, yielded the cis-isomer (10) (16%) and transisomer (11) (28%). Reduction of (10) with lithium aluminium hydride in tetrahydrofuran followed by acetylation with acetic anhydride and pyridine gave two epimeric acetates (12) (32%) and (13) (52%) whose configuration was determined by NMR spectroscopy. Oxidation of (12) with Jones reagent afforded ketone (14) which was converted to the a, 3-unsaturated ketone (15) by bromination with pyridinium tribromide in dichloromethane followed by dehydrobromination with lithium carbonate and lithium bromide in dimethylformamide. Ketone (15), on catalytic hydrogenation with Pd-C in the presence of perchloric acid, produced compound (16) (72%) and (14) (17%). The compound (16) was converted to alcohol (17) by reduction with lithium aluminium hydride. 

Spectra of the linear anion FHF in the gas phase were obtained by diode laser spectroscopy P = 583.6539(13) cm, uj = 1286.0284(22) cm , and 1 3 = 1331.1502(7) cm . From the resulting rotational constants an equilibrium F-F intemuclear distance of 227.771(7) pm was calculated (Kawaguchi and Hirota, 1987). In the class of binary hydrides, boron compounds are especially interesting. A recent FTIR investigation revealed the out-of-plane vibration of unstable BH3 1140.8757(39) cm (Kawaguchi et al., 1987). These data confirm the results of a recent matrix study which showed an absorption at 1132 cnr for the same vibration (Kaldor and Porter, 1971). A detailed... 

Heavy metals, boron (B(V)), arsenic and total phosphorus were determined in the fraction < 20 pm to improve the comparability of the results. This fraction was separated from the freeze-dried and non-milled samples by ultrasonic sieving (Ackermann 1980). Metals were analysed after microwave-assisted digestion with aqua regia at 180 °C in closed vessels by inductively coupled plasma optical emission spectroscopy, atomic fluorescence spectroscopy (mercury) and hydride atomic absorption spectroscopy (arsenic). 

After the dehydrogenation reaction of LiBIij, the end-products, lithium hydride (LiH) and boron, were rehydrogenated at 873 K under 35 MPa for 12 hours or at 1000 K under 15 MPa for over 10 hours to form LiBH4. The rehydrogenation reaction was confirmed by Raman spectroscopy and PXD measurement. The modified lithium borohydrides, LiBH475% -i- Ti0225%... 

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