What is the coordination number of the metal ion in an octahedral complex ? Why does `NH_(3)` take part in complex formation but not `NH_(4)^(+)`?

Explanation

The coordination number of the metal ion in an octahedral complex = 6.
`NH_(4)^(+)` ion does not take part in complex formation because (1) unlike `NH_(3)`, the N-atom of `NH_(4)^(+)` does not have any lone pair of electrons. (2) The positive charge on `NH_(4)^(+)` gets repelled by the positively charged metal ion.