This is a special type of covalent bond where the shared pair of electrons are contributed by one species only but shared by both. The atom which contributes the electrons is called the donor (Lewis base) while the other which only shares the electron pair is known as acceptor (Lewis acid). This bond is usually represented by an arrow (→) pointing from donor to the acceptor atom.
BF3 molecule, boron is short of two electrons. So to complete its octet, it shares the lone pair of nitrogen in ammonia forming a dative bond.
Characteristics of co-ordinate covalent compound
(1) Their melting and boiling points are higher than purely covalent compounds and lower than purely ionic compounds.
(2) These are sparingly soluble in polar solvent like water but readily soluble in non-polar solvents.
(3) Like covalent compounds, these are also bad conductors of electricity. Their solutions or fused masses do not allow the passage to electricity.
(4) The bond is rigid and directional. Thus, coordinate compounds show isomerism.