The number of ligands attached to a metal is known as the coordination number
of the metal.
The charge of a complex is the sum of the charges on the central metal and on its
surrounding ligands. Thus given the charge on the complex and the ligands we can
calculate the charge on the metal (known as its oxidation number ).
For complex cations and complex anions the charge on the complex may be deduced
from the charge on the compound and
the charge on the other ions in the compound (to achieve overall neutrality).
eg. . In [Cu(NH3)4]SO4 we can deduce the charge
on the complex if we first recognize SO4 as representing the sulfate ion
and therefore having a 2- charge. Because the compound is neutral,
the complex ion must have a 2+ charge,
[Cu(NH3)4]2+. We can then use the charge of the
complex ion to deduce the oxidation number of copper. Because the NH3 ligands
are neutral, the oxidation number of copper must be +2:
