Q.What characteristics do you expect from an electron-deficient hydride with respect to its structure and chemical reactions?

An electron-deficient hydride (typified by group 13 hydrides such as B2H6, Al2Cl6-type bridging, etc.) does not have enough valence electrons on the central atom to form a complete octet using ordinary two-centre, two-electron (2c-2e) bonds to every hydrogen.

Structural characteristics expected:

• The molecule compensates for this shortage by forming multicentre bonds — most famously the 3-centre-2-electron (3c-2e) "banana" bridge bonds seen in diborane, where a pair of electrons is shared among three atoms (B–H–B) rather than just two.
• This gives such hydrides distinctive, often bridged or cluster-type, three-dimensional structures rather than simple linear/tetrahedral geometries.

Chemical reactivity expected:

• Because the central atom still effectively "wants" more electron density to complete its octet, electron-deficient hydrides behave as strong Lewis acids (electron-pair acceptors). …

Reason from the electron shortfall: since normal bonds can't be formed to every H, expect bridge/multicentre bonding structurally, and Lewis-acid (electron-pai …

• Describing the bonding as simple covalent bonds without mentioning the multicentre/bridge nature that is the hallmark of electron deficiency. …