Diborane(2) is an inorganic compound having the formula B2H2. It has a symmetric covalently bonded structure of HBBH, with a double bond between the two boron atoms and one hydrogen atom bonded to each boron. This compound is unique among the analogous formulas for other elements of the boron group, and also unlike higher boranes such as diborane(6) (B2H6), in that it has a direct boron–boron bond rather than bridging hydrides. The boron–boron bonding in this compound is also a rare example of a pure pi bond, one that does not have any net sigma bonding associated with it.
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