Cu2+ + 4 NH3 Cu(NH3)42+

Practice Problem 2:
Calculate the charge on the transition-metal ion in the following complexes.
(a) Na2Co(SCN)4
(b) Ni(NH3)6(NO3)2
(c) K2PtCl6
G. N. Lewis was the first to recognize that the reaction between a transition-metal ion and ligands to form a coordination complex was analogous to the reaction between the H+ and OH- ions to form water. The reaction between H+ and OH- ions involves the donation of a pair of electrons from the OH- ion to the H+ ion to form a covalent bond.
The H+ ion can be described as an electron-pair acceptor. The OH- ion, on the other hand, is an electron-pair donor. Lewis argued that any ion or molecule that behaves like the H+ ion should be an acid. Conversely, any ion or molecule that behaves like the OH- ion should be a base. A Lewis acid is therefore any ion or molecule that can accept a pair of electrons. A Lewis base is an ion or molecule that can donate a pair of electrons.
When Co3+ ions react with ammonia, the Co3+ ion accepts pairs of nonbonding electrons from six NH3 ligands to form covalent cobalt-nitrogen bonds as shown in the figure below.
The metal ion is therefore a Lewis acid, and the ligands coordinated to this metal ion are Lewis bases.
The Co3+ ion is an electron-pair acceptor, or Lewis acid, because it has empty valence-shell orbitals that can be used to hold pairs of electrons. To emphasize these empty valence orbitals we can write the configuration of the Co3+ ion as follows.

Co3+: [Ar] 3d6 4s0 4p0

There is room in the valence shell of this ion for 12 more electrons. (Four electrons can be added to the 3d subshell, two to the 4s orbital, and six to the 4p subshell.) The NH3 molecule is an electron-pair donor, or Lewis base, because it has a pair of nonbonding electrons on the nitrogen atom.

Dmg Is Which Type Of Ligand Used

According to this model, transition-metal ions form coordination complexes because they have empty valence-shell orbitals that can accept pairs of electrons from a Lewis base. Ligands must therefore be Lewis bases: They must contain at least one pair of nonbonding electrons that can be donated to a metal ion.

Dmg Is Which Type Of Ligand C