Diborane (B2H6) is a classic example of an inorganic dimer. Borane does not exist alone as BH3, even though it is often written in that way. B2H6 exists as a structure where two hydrogen atoms bridge the two boron atoms. The bridging B-H bonds are lower in bond order than what would be expected for a regular B-H bond (they are lower in bond order than the terminal B-H bonds). This is explained by the bond having three centers but only two electrons, "banana bond", instead of the typical single bond with two centers and two electrons.
