Coordinate bond

Coordinate bond aka dative bond. A bond where lone pair of electrons sticks into an empty orbital of an electron deficient atom in a molecule.
Prime example is Nitrogen forming a coordinate bond with boron.

This is in contrast to simple covalent bonds where electrons are shared symmetrically.
Two electrons one from each atom pair up. Electron spins must align antiparallel.

Electron deficiency can lead to more complex things like
two electron three center bonds.

External Links

• Coordinate covalent bond
• Coordination polymer
• Metal–organic framework