What is a #"coordinate covalent bond"#?

1 Answer
Oct 25, 2016

A co-ordinate covalent bond is a 2-centre, 2-electron bond in which the 2 electrons formally derive from the same atom.

Explanation:

This is best illustrated with an example: consider the basicity of ammonia:

#NH_3(aq) + H_2O(l) rightleftharpoons NH_4^+ + HO^-#

In the forward equilibrium, ammonia has bound a proton to form the ammonium ion. In #NH_4^+# all the hydrogen atoms are equivalent, yet the 2 electrons that form one of the #N-H# derive from the lone pair on the nitrogen. Coordination chemistry is replete with examples of #"coordinate covalent bonds"#, or #"donative"# or #"dative"# bonds, i.e. the hexaqua transition metal complexes, #[M(OH_2)_6]^(2+)#, in which a lone pair on the oxygen donor forms a covalent bond with the metal centre.