Boron Hydrides
Definition and meaning of Boron Hydrides in chemistry.
Boron hydrides, also called boranes, are covalent compounds of boron and hydrogen that are electron-deficient, meaning they lack enough valence electrons to form a conventional two-electron bond between every pair of adjacent atoms.
In more detail
Because each boron atom contributes only three valence electrons, boranes satisfy their bonding requirements using unusual three-center two-electron (3c-2e) bonds, in which a bridging hydrogen atom links two boron atoms through a single shared electron pair delocalized over all three atoms. This bonding motif, sometimes called a "banana bond," produces open cage and cluster structures rather than simple chains. Boranes range from small molecules like diborane to larger polyhedral clusters such as decaborane and various borane anions, and they are typically reactive, flammable, and readily hydrolyzed. William N. Lipscomb won the 1976 Nobel Prize in Chemistry for determining borane structures and explaining their bonding.
Key facts
| Formula | B2H6 (diborane, simplest borane) |
|---|---|
| Field | Inorganic Chemistry |
| Key bonding feature | Three-center two-electron (3c-2e) bridging bonds |
| Notable recognition | W. N. Lipscomb, 1976 Nobel Prize in Chemistry |
Diborane, B2H6, consists of two BH2 groups connected by two bridging hydrogen atoms, each bridge held together by a three-center two-electron bond rather than an ordinary single bond.
Frequently asked questions
Why are boron hydrides described as electron-deficient?
Boron has only three valence electrons per atom, too few to form a standard two-electron bond to each neighboring atom, so boranes use delocalized three-center two-electron bonds involving bridging hydrogens instead.
What is the general formula for boranes?
Neutral boranes fall into series such as BnHn+4 (arachno-type, e.g., B2H6, B5H11) and BnHn+6 (nido-type, e.g., B5H9, B10H14), depending on cluster shape.