Looking at the nickel complexes as an example it is found th

Looking at the nickel complexes as an example, it is found that those formed with ammonia give the complex [Ni(NH3)6]^2+ and when formed with ethylenediamine the complex [Ni(en)3)^2+ is the result. Even though both are octahedran complexes, why do you think that nickel is coordinated with six ammonia ligands in one case and only three ethylenediamine ligands in the other?

Solution

because ethylenediamine are bidentate ligands and have 1 ethylenediamine molecule uses up two Ni bonding arms