Electron diffraction, boron hydrides

The systematic principles of boron hydride structures ahd chemistry are the principal subjects of the present review. There are several reasons why these principles became clear such a long time after the discovery of these compounds (a) most of the compounds must be handled in grease-free vacuum line systems (b) some of the boron hydrides are unstable at ordinary temperatures, explosive on contact with air, and toxic (c) the structures are based on principles, still incompletely developed, of electron-deficient compounds and (d) location of the hydrogen atoms is a crucial part of the structure determinations, unlike the situation in hydrocarbons, and had to be done for the most part in X-ray diffraction studies of single crystals grown at low temperatures. 

The actual chemical structures of boron hydrides remained a mystery for decades. The obvious analogy of the formula of diborane(6), B2H6, to ethane and of tetraborane(lO), B4H10, to butane tempted speculation that the structures were also analogous. In fact, electron diffraction studies appeared to bear this out for B2H6, whieh was incorrectly reported to have the ethane structure. 

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