Borane

A boron hydride. Many boranes have multicentre bonding, so their composition and cage geometry cannot be reconstructed using only independent ordinary two-centre B–B bonds.

$[{\mathrm{B}}_{12}{\mathrm{H}}_{12}{]}^{2-}$ has 26 skeletal electrons and a closo icosahedral B12 framework.

A borane-derived cluster containing skeletal carbon vertices. In a simple neutral count, a CH vertex contributes three skeletal electrons while BH contributes two.

A carborane-derived cage with one or more metal vertices. An external ligand such as cyclopentadienyl is not counted as five additional cage vertices.

A metallacarborane containing a cobalt vertex. CpCo can replace BH in a suitable isolobal skeletal-electron count.

The open-face dianion $[{\mathrm{C}}_2{\mathrm{B}}_9{\mathrm{H}}_{11}{]}^{2-}$ can bind through its five-membered open face as an ${\eta }^5$, six-electron donor. Capping this face with a metal fragment completes a 12-vertex metallacarborane; two faces can also support a bis(dicarbollide) metal donor.

A closed deltahedral carborane. Thermal conversion of nido precursors may change hydrogen content or cage size as well as carbon positions.

An open carborane cage with the nido skeletal-pair count. Mild alkyne–borane reactions can preserve adjacency of newly incorporated carbon atoms.

${\mathrm{B}}_6{\mathrm{H}}_{12}$, a six-vertex arachno borane with nine skeletal pairs. Bridge deprotonation gives the undecahydrohexaborate anion.

$[{\mathrm{B}}_6{\mathrm{H}}_{11}{]}^{-}$, an arachno borane anion with nine skeletal pairs. A localized BH3-adduct drawing does not describe its lowest-energy fluxional cage adequately.

$[{\mathrm{B}}_5{\mathrm{H}}_8{]}^{-}$, the bridge-deprotonated conjugate base of pentaborane(9). Its five-vertex framework has seven skeletal pairs and is nido.

${\mathrm{B}}_5{\mathrm{H}}_9$, a nido borane with a square-pyramidal boron skeleton. A bridging proton can be removed to form $[{\mathrm{B}}_5{\mathrm{H}}_8{]}^{-}$.