Ligand and Complex Ions Questions ?

Question

If the coordination number is a metal is 6, how many ethylenediamine molecules and how many ethylenediaminetetraacetate ions will bind to the metal ion in a complex?

Ammonia is a stronger ligand than is the chloride ion. What does this mean?

I assume the answer to number to has to do with the basicity of the ammonia...

Thank you in advance!

Answer 1

Also, here is the order of the strength of ligands:

I- < Br- < Cl- < F- < OH- < H2O < NH3 < en(ethylenediamine) < NO2- < CN- < CO

CO being the strongest ligand and Iodide being the weakest. This relates to the crystal field splitting Δ. The electrical field of stronger ligands pushes the 5 d orbitals down in energy and repulses them. This can be related to high spin and low spin complexes.  

Answer 2

If the coordination of a metal is 6 then this means that there will be 3 ethylenediamine ligands to bond to the metal.

Ethylenediamine is a bidentate which means it can bind at two different locations to the metal.

Ethylenediamine is :NH2-CH2-CH2-NH2:

The N atoms bind to two different places on the metal center so there is only a possibility of three locations because the coordination is 6 (2 x 3)

If you have ethylenediaminetetraaceteate then only one molecule is available for bonding.

The formula is  2(OOCCH2)NH2-CH2-CH2-NH2(CH2COO-)2

The two N atoms and the four O atoms from the COO- group attach themselves to the metal center. Check out this image

http://cache.eb.com/eb/image?id=16451

Ammonia is a strong field ligand because it is a good pi-acceptor ligands(with respect to Cl) Cl is a better pi-donor than it is a pi-acceptor.

This all comes out of crsytal field theory and the relative energies of the molecular orbitals that are formed from the overlap of the metal's d orbitals and the ligands pi orbitals.