Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless and highly unstable gas at room temperature with a sweet odor. Diborane mixes well with air, easily forming explosive mixtures, diborane will ignite spontaneously in moist air at room temperature. Synonyms include boroethane, boron hydride, and diboron hexahydride, diborane is a key boron compound with a variety of applications. The compound is classified as endothermic, meaning that its heat of formation, diborane adopts a D2h structure containing four terminal and two bridging hydrogen atoms. The model determined by molecular orbital theory indicates that the bonds between boron and the hydrogen atoms are conventional 2-center, 2-electron covalent bonds. The bonding between the atoms and the bridging hydrogen atoms is, however, different from that in molecules such as hydrocarbons. Having used two electrons in bonding to the hydrogen atoms, each boron has one valence electron remaining for additional bonding. The bridging hydrogen atoms provide one electron each, thus the B2H2 ring is held together by four electrons, an example of 3-center 2-electron bonding. This type of bond is called a banana bond. The weakness of the B-Hbridge vs B-Hterminal bonds is indicated by their signatures in the infrared spectrum, being ~2100 and 2500 cm−1. The structure is isoelectronic with C2H62+, which would arise from the diprotonation of the planar molecule ethene, diborane is one of many compounds with such unusual bonding. Of the other elements in Group IIIA, gallium is known to form a compound, digallane. Aluminium forms a hydride, n, although unstable Al2H6 has been isolated in solid hydrogen and is isostructural with diborane. Extensive studies of diborane have led to the development of multiple syntheses, most preparations entail reactions of hydride donors with boron halides or alkoxides. 2 BH4− +2 H+ →2 H2 + B2H6 Similarly, oxidation of borohydride salts has been demonstrated and remains convenient for small scale preparations. For example, using iodine as an oxidizer,2 NaBH4 + I2 →2 NaI + B 2H6 + H2 Another small-scale synthesis uses potassium hydroborate, diborane is a highly reactive and versatile reagent that has a large number of applications. Its dominating reaction pattern involves formation of adducts with Lewis bases, often such initial adducts proceed rapidly to give other products
Image: Diborane 2D
Image: Diborane 3D balls A
Bonding diagram of diborane (B2H6) showing with curved lines a pair of three-center two-electron bonds, each of which consists of a pair of electrons bonding three atoms, two boron atoms and a hydrogen atom in the middle.