Selected Topic in Depth Electron-Deficient Compounds

SELECTED TOPIC IN DEPTH ELECTRON-DEFICIENT COMPOUNDS  

The principal characteristic that distinguishes the Group 3A elements from the rest of the representative elements is the existence of electron-deficient compounds. You may recall earlier references, in this book and elsewhere, to compounds of this type. It is not unusual for boron, aluminum, gallium, and occasionally beryllium and lithium to form compounds in which the metal is surrounded by less than an octet of electrons. One should of course be wary of such phrases as electron-deficient. It seems to imply that there is something wrong with such compounds. In fact, it is 

The first borohydrides were synthesized by Alfred Stock, a German chemist active in the first third of the twentieth century. He prepared a mixture of boranes by the reaction of magnesium boride, MgB2, with various mineral acids, as shown in Equation (14.19)  

MgB2 + HCl -------- mixture of B4Hio,B5H9,B5Hii,B6Hio, and B10H14 ILHM 

Note that no BH3 (which would be called borane, consistent with compounds such as methane, CH4) was formed as might be expected. Upon heating B4HJ0 to 100°C, it decomposes to a compound of that empirical formula, but its molecular formula is B2H5 and consequently it is called diborane. 

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