Explain the structures of diborane and boric acid.

(N/A) $B_2H_6$ is an electron-deficient compound. It has only $12$ valence electrons: $6$ from $6$ $H$ atoms and $3$ each from $2$ $B$ atoms. Thus,after forming $3$ terminal $B-H$ bonds,the boron atoms have no electrons left for bridging. $X$-ray diffraction studies reveal the structure of diborane:
$1$. Two boron and four terminal hydrogen atoms $(H_t)$ lie in one plane.
$2$. The two bridging hydrogen atoms $(H_b)$ lie in a plane perpendicular to the plane of the boron atoms,one above and one below.
$3$. The terminal bonds are regular two-centre two-electron $(2c-2e^-)$ bonds.
$4$. The two bridging $(B-H-B)$ bonds are three-centre two-electron $(3c-2e^-)$ bonds,often called banana bonds.
Boric acid $(H_3BO_3)$:
Boric acid has a layered structure. Each planar $BO_3^{3-}$ unit is linked to others through hydrogen bonds. The $H$ atoms form a covalent bond with oxygen in one $BO_3$ unit,while forming a hydrogen bond with oxygen in another $BO_3$ unit. The dotted lines in the structure represent these hydrogen bonds.